Radon in Iowa (U.S.A.)

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Radiation Protection
Radon in Iowa, Why Should I be Worried
Master Degree in Nuclear Engineering
Prof. Romolo Remetti
Student: Sabino Miani
Academic Year: 2016/2017

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Table of Contents
Summary……………………………………………………………………………………………………3
1. A Brief History of Radiation Protection…………………………………………………………………4
2. Sources of Radioactivity…………………………………………………………………………………5
2.1. Terrestrial and Extraterrestrial Sources……………………………………………………………..6
3. What is a NORM………………………………………………………………………………………...7
4. Why Radon……………………………………………………………………………………………....8
4.1. Radon Isotopes……………………………………………………………………………………...9
5. Why Iowa………………………………………………………………………………………………..11
6. The Geology of Radon…………………………………………………………………………………..15
7. Why are Radon Levels so High in Iowa………………………………………………………………...17
7.1. Different Types of Soils…………………………………………………………………………….18
7.2 Landform Regions in Iowa…………………………………………………………………………..20
8. Why is Radon Considered so Dangerous………………………………………………………………..24
9. Correlation Between Causes and Effects………………………………………………………………...28
10. Epidemiology and Epidemiological Investigations…………………………………………………….30
11. Laws and Regulations…………………………………………………………………………………..31
11.1. Italy………………………………………………………………………………………………...31
11.2 United States………………………………………………………………………………………..32
12. Concerning EPA………………………………………………………………………………………..34
12.1. The Making of Regulations………………………………………………………………………..34
12.2. EPA’s Organization………………………………………………………………………………..35
13. How is Radon Concentration Calculated……………………………………………………………….38
14. Radon in Homes………………………………………………………………………………………...45
14.1. Living in the Same Home…………………………………………………………………………..46
14.2. Buying, Building or Selling a Home……………………………………………………………….52
15. Radon in Schools………………………………………………………………………………………..53
Conclusions…………………………………………………………………………………………………54
References
Appendix A

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Summary
As the title of this work shows, the subjects of this relation are radon and Iowa. In fact, radon
is a major problem in the United States, and in particular in the Iowa state. However, most
people do not even know the existence of this silent killer, being an odorless and colorless gas.
Furthermore, being the argument very wide, a person not involved in the field, might get lost
between equations and definitions. This is why this work has been structured in a certain way.
In fact, most of the titles related to this work’s chapters have been presented as questions.
Indeed, the idea was to create a sort of “giant FAQ” paper. In this work, every chapter
represents the answer to the question given in each corresponding title. In particular, the titles
(i.e. the FAQ) have not been chosen randomly. In fact, the “path” followed to build the table
of contents, tries to recreate the typical questions that might come into mind when an
individual becomes interested in the radon problem.
Considering the specific chapters now, the reasons why radon levels are so high in Iowa shall
be explained, taking into account the geology and history of Iowa. Consequently the solutions
developed to reduce radon levels shall be analyzed. However, not before reasoning the choices
made (about the two subjects) and understanding why radon is considered a threat to human
health. Moreover, an overall explanation of the laws and regulations will be also given
(focusing on Italy and United States) since through these, regulatory agencies protect
individuals and the environment (from health hazard substances, such as radon). Finally, we
shall see how the radon problem is managed in practical situations, such as houses and schools.

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1. A Brief History of Radiation Protection
After Mendeleev introduced the periodic system of elements in 1869, scientists all over the
world (mostly between Europe and the United States) made a series of discoveries concerning
atomic and nuclear physics. At the end of 1895 for example, Wilhelm Roentgen discovered
by accident some properties of x-rays; it was then the turn of Henri Becquerel, which noticed
that uranium salts emitted rays similar to the ones discovered by Roentgen, only in a
spontaneous way (instead of a ‘forced’ one). However, at first he abandoned this idea, thinking
the emission was caused by extended sun exposure. After additional experimentation, he
concluded that those rays were naturally emitted by uranium: he had discovered radioactivity
(term coined years later by Marie Curie).
As often happens in these fields, when a new “subject” is brought to light, together with the
pure scientific discovery comes the somehow necessity to apply it (to make it useful/to find a
way to use it). While on one hand, the beneficial use of ionizing radiations was being
appreciated in the most disparate fields (e.g. medical, scientific and industrial); on the other
hand, it was becoming clear that these benefits were not priceless. In fact, if not handled
properly, sources of radiations could be a potential threat to human health; the first to
experience these effects were scientists (due to exposure to radioactive materials), operators
(due to x-ray exposure) and eventually patients. Nevertheless, it was not until the World War
I that the risk related to ionizing radiations was brought to public attention. During this period
of time the United States Radium Corporation developed a paint that could glow in the dark
(it was a radioactive paint made by a mixture of radium and zinc sulfide) used to light up
instruments (especially the dials of watches). The painting job was designated mostly to
women (the so called “radium girls”), who were unaware of the risks they were taking, since
they had been told the paint was harmless. They used to lick the paintbrushes to model them;
consequently, small quantities of radium were swallowed. This element tends to accumulate
in bones (since calcium and radium have the same external electronic composition, radium can
be fixed instead of calcium), and this led to radiation sickness. Many of the women died of
anemia and diseases related to mouth, but these deaths were at first attributed to other causes
(such as syphilis). In 1925, a report was published in which the deaths were related to the
ingestion of radioactive material. This, as well as further examinations, brought the public
attention towards the danger associated with radioactivity. Nonetheless, the path that was
chosen was the one that implied the effort to understand the effects induced by radiation on
biological tissues, and how to protect the people; and that meant research. A research whose
goal was, above all, to set up rules or guidelines to follow in order to protect people (e.g. in
the medical field, where x-ray devices where widely being used).

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At the same time, the first organizations started to rise; these were created in order to protect
people from the harmful effects of ionizing radiations. Among these stood The British
Roentgen Society, whose goal was the protection against x-ray exposure (since in that period,
x-ray devices were commonly used; the effects induced by these sources of radiations,
following an extended exposure, were known). Then the American Organization followed,
which decided to approve the same guidelines established by The Roentgen Society. However,
since the radiation protection was not yet a government’s “duty”, these were non-governmental
organizations. Things changed after World War II, the Federal Radiation Council was set up
to serve as a reference, in the radiation field (concerning the use of radiations, and the problems
related to it). A few years later, the first federal agency was created. The aim of this agency
was to protect people and environment from the harmful effects of ionizing radiations (even
though this was the goal of one of the sections of this agency, in particular the one dedicated
to the radiation field); this bureau was called U.S. Environmental Protection Agency,
shortened in EPA.
2. Sources of Radioactivity
From the previous chapter, it may seem that the danger associated with the use of sources of
ionizing radiations is only related to those activities that involve devices made by individuals
(i.e. anthropic activities). An example could be the x – ray devices used in the medical field.
We have seen how the radiation protection evolved, starting with simple rules that had to be
followed, while using x-ray devices (these were the principles of distance, time and
protection), to make sure these devices were used in the safest way possible; and ending up
with actual guidelines made by certain institutions (non-governmental at first). These
guidelines became real limits after the first atomic bomb and the first nuclear pile (Chicago
Pile n.1) were build. However, the radiation protection’s purpose does not end with anthropic
activities of course, since we are literally surrounded by radiation fields (defining this as the
portion of space through which the ionizing radiations move). The sources of these ionizing
radiations can be found in the construction materials, in the soil, in the atmosphere, in the
water, etc. We can, in fact, identify as much as 60 different radionuclides (and even more), in
the environment surrounding us.

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These radionuclides are unstable nuclei that undergo a process called decay, through which
they reach a more stable configuration. The decay process comes with the emission of a so
called recoil nucleus and one or two ionizing radiations (depending on the parent nucleus).
These particles (ionizing radiations) are the ones related to human health’s problems, but we
will discuss about this later.
Now, as one might imagine, the origination of these radionuclides is different; we can therefore
identify different families of radionuclides based on how they were ‘created’. As we said
before, we can recognize natural sources and artificial ones (which includes artificially made
radionuclides, which cannot be found in the environment). Referring now only to the former,
we can follow two paths. These two paths lead to different types of radionuclides called:
▪ Cosmogenic radionuclides;
▪ Primordial radionuclides (since there are also stable primordial nuclides) together with
their daughters.
The latter are the ones responsible for the production of the subject of this work: 222
Rn. In the
next paragraph, we shall see in more detail how these radionuclides are created, focusing on
the primordial decay chains.
2.1. Terrestrial and Extraterrestrial Sources
The cosmogenic radionuclides are the ones found in the atmosphere (we are talking about the
lowest layer of atmosphere, which is the one closer to the earth’s crust). These radionuclides
are the result of the interaction of the so called ‘secondary cosmic radiation’ and the lowest
layer of the atmosphere. The secondary cosmic radiation is primarily made of electrons,
protons, neutrons and photons; the last ones more easily avoid interactions and may reach the
earth’s crust. In fact, while the first three interact through the coulomb field (always present)
so that their way of interacting is defined as ‘continuous’, neutrons and photons interact in a
‘stochastic way’, that is they interact only if they “hit a particle”.
Still proceeding backwards, this secondary cosmic radiation derives from the reactions that
take places in the upper atmosphere, (farthest from the earth’s crust) between this (atmosphere)
and the ‘primary cosmic radiation’.

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The particles associated with this primary cosmic component, have two sources:
▪ Solar, that is sun eruptions (mostly solar flares), in which high energy particles and
nuclei (plasma), emitted by the sun, interact first with the earth’s magnetic field and
then (the fraction that passes the magnetic field) with the earth’s upper atmosphere;
▪ Extra solar, due to supernovas explosions.
These particles are mostly protons, alpha particles (helium nuclei) and heavy nuclei. All these
processes, in cascade, give rise to the cosmogenic radionuclides nominated before. These
radionuclides usually have half-lives smaller than the ones belonging to the primordial decay
chains. Some of these cosmogenic radionuclides are 14
C, 3
H (both incorporated thanks to the
food chain) and 7
Be.
We may now concentrate on the ones present in the earth’s crust; these are part of the
primordial decay chains. Some of which have really long half-lives, on the order of hundreds
of millions of years (e.g. 238
U).
3. What is a NORM?
We have now ‘gained’ a sufficient number of elements to describe the ‘natural background’.
The sources described in the previous chapter, for example, are defined as ‘natural background
sources’. The term refers indeed to the fact that these radiations are emitted “by the
environment” surrounding us (quotation marks are due to the fact that actually, the radiation
is emitted by the radionuclides found in soils, water, atmosphere, etc... and so indirectly by the
environment).
Now, of all the natural background sources, a distinction needs to be made. The reason for this
is related to the fact that some of them occur in concentrations (in certain materials) such as to
be considered a hazard for human health. These materials (such as certain types of rocks for
example), in which radionuclides reach these concentrations, are defined as “Naturally
Occuring Radioactive Materials”, that is NORM. They are consequently subjected to ‘special’
requirements. The materials in question may contain a single specie of radionuclides (this is
the case of 40
K) or a large number of them. The latter refers to materials containing elements
deriving from the decay of primordial radionuclides, showed in the figures below (i.e. 238
U,
232
Th and 235
U). These primordial decay chains are presented in the next page.

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4. Why Radon?
Until now, we have come to understand what kind of radiation sources we have to deal with
and mostly where these sources come from. We have seen how there are two ‘big families’ of
radionuclides, which give rise to the natural background. Of these families, we will concentrate
on the one responsible for the production of radon (222
Rn in particular). Since radon, as we
have already seen, is the major subject of this work. Therefore, the first question that may
come in mind is: “We have just finished describing how many health hazard radionuclides are
‘scattered’ all over the world, so why radon in particular?”. The goal of this chapter is to
answer this precise question.

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Now, looking at the decay series showed in the previous section, we could easily see how
much the half-life varies from chain to chain and also in the same chain, from element to
element. For an instance, we might find:
▪ 238
U, 232
Th and 235
U, whose half-lives are incredibly long if compared to an average
human life;
▪ 216
Po, 218
Po and 215
Po which are characterized by really short half-lives;
▪ Others that might be found in the middle.
Now, recalling the relation between the activity of a certain type of radionuclide and his half-
life:
𝑎(𝑡) = 𝜆𝑁(𝑡) = 𝜆𝑁0 𝑒−𝜆𝑡
=
𝑙𝑛(2)
𝑡1/2
𝑚
ℵ
𝐴
The first thing that comes into mind, when looking at this equation, is that radionuclides
belonging to the first group are characterized by really low activity, while the ones related to
the second group happen to have really high activity but really small half-lives. We may thus
conclude that these groups are of no interest in term of radiation protection (even though this
also depends on their activity concentration). Actually, the ones that form the second group
are of extreme importance in radiation protection, but it happens to be so only because a certain
radon isotope has the capability to reach the atmosphere (since their source is the soil);
otherwise their chemical-physical characteristics would not allow them to reach the surface.
The polonium element for instance, is ‘generated’ in the solid phase (is a metalloid) and the
diffusion coefficient (in the soil) is really low for this kind of elements.
Let us focus now on the radon isotopes, which belong to the third group, in order to understand
things better.

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4.1. Radon Isotopes
From the three pictures depicted in the third chapter, representing the three primordial decay
series, it can be easily seen how radon appears in all of them (we refer to the radon element,
since every series contains one of the three isotopes). Later on we will concentrate only on the
isotope belonging to the 238
U series (i.e. 222
Rn), and in this section we shall explain why.
Let us start considering the two major elements of those series, uranium and thorium, known
as primordial elements.
▪ Uranium, which is a metal (from the actinide series), can be found in the environment
(considering standard conditions of pressure and temperature) in the solid phase. The
so called natural uranium (the element) is composed by the three isotopes 238
U, 235
U
and 234
U, whose abundance is respectively equal to 99,275%, 0,72% and 0,005%.
Considering that 234
U belongs to the 238
U decay chain, we will only consider the first
two isotopes. These two isotopes are the fathers of two out of three primordial decay
chains. Now, taking into account the abundance of these isotopes, and considering that
the two radon isotopes (222
Rn and 219
Rn respectively) derive from these chains, we
might leave out the 219
Rn. His abundance in nature is related to the one of the 235
U
isotope, indeed really low if compared to the one of the 238
U isotope.
▪ Thorium, just like uranium, is a metal that belongs to the actinide series, also found in
the solid phase. There is only one isotope (232
Th); therefore, his abundance is 100%.
Uranium and thorium can be found almost everywhere in the environment, being present in
the rocks (and consequently into the soil) and in the water. However, the latter is approximately
10 times more abundant than the former. The radon isotope belonging to the thorium decay
chain is the 220
Rn. Therefore, if we were to consider only these characteristics, we would easily
deduce that the 220
Rn isotope is the one on which we shall focus, from the radiological (impact)
point of view.
The conclusions at which we will arrive at the end of this chapter are quite different, and the
reason for this can be understood analyzing the three radon isotopes, in particular their half-
lives.
▪ 219
Rn: this isotope belongs to the actinium decay chain. Being a gas (radon), when at
first it was discovered, it was simply believed to be emanated by (in this case) actinium.
Later on, they found out it was a different element (the same thing happened for the
other two isotopes). That is why it was called ‘Actinion’ at first. Now, the half-life of
this isotope is really small (3,98s versus the 3,83d of the 222
Rn), and so it is his
abundance in nature. This mostly shows why we can ignore this isotope, from a
radiological point of view.

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▪ The 220
Rn isotope, called ‘Thoron (for the same reason as above), belongs to the thorium
decay chain. His half-life (55,8s) and his activity concentration (in the environment) are
larger than the ones of the former isotope; but still, not enough if compared to the isotope
belonging to the fertile isotope of uranium.
Considering now the radiation protection’s field, how can we relate the half-life and the
activity concentration of these isotopes, to the fact that some of them are considered more
health hazard than others? We have seen how all of these isotopes are ‘created’ into the soil,
since the three fathers of the decay chains are present in rocks. Moreover, we shall see why,
especially in closed environments, radon can be a serious problem for human health. From the
two statements above we can easily come to understand how an isotope, being a noble gas,
and also characterized by long half-life (if compared to the other two) and high concentration,
can more easily move out of the soil and escape the surface before decaying. Since the upward
movement is not as easy as one might think, high concentration and long half-life determines
a major concentration in the environment (the surface) of a certain isotope, and consequently
a major problem for human health. Nevertheless, this is just an anticipation; we shall focus on
this matter later on.
5. Why Iowa?
We have seen, until now, all different kind of radiation sources that can be found in the
environment surrounding us. We have come to understand how radionuclides are present
almost everywhere, from food to water, from atmosphere to soil and construction materials.
In addition to these sources, we have also mentioned a number of ‘anthropic sources’ or man-
made sources. For example medical devices (x-ray generators, to give one example), smoke
detectors (which exploit the decay of 241
Am to detect smoke), and of course coal and nuclear
power plants (the inorganic part of coal, i.e. the ashes that remain after burning it, contain a
certain amount of radionuclides). The reason why we have done this will be clear soon.
In the introduction, we have given a brief summary of what the goal of this work was going
be. Now, before reaching the core of this paper we need to understand why certain choices
have been made. One of them gets the answer in this chapter. In particular, we need to
understand why the choice has fallen upon Iowa. The table presented in the next page shows
all the contributions to what we call the ‘annual average dose’ per person. Some of these
contributions have been pointed out above. The only contribution that does not appear, is the
one that comes from radon, but this is because it will be taken into account in the subsequent
chart.

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The unit of measure presented is the millirem [mRem], used for the effective dose (used to
quantify potential consequences of radiations interacting with the body as a whole; it weighs
the absorbed dose based on the type and energy of the particles interacting and on the organs
targeted). This unit of measure is widely used throughout the United States, we shall convert
the result in millisievert for completeness, since it is part of the International System of Units.
Therefore, keeping the radon out, the radiation sources together with the values of dose
associated with them are the following:
Medical Field Exams or Medical Procedures (e.g. x-ray
generators)
No 0
Terrestrial (Soil) Country of Residence (USA) IA 46
Cosmic Rays (From
Space)
Country Elevation (average value of the
country)
Up to
1000ft
2
Incorporated Dose
(Body)
From food and water e.g.
potassium
40
Fake teeth or porcelain crowns No 0
Sources Related to
Flights
Average Distance Traveled by plane in a year
(miles)
2000 2
Going through screening machines in airport 2 0,006
X ray luggage inspection machines in the
airport
Yes 0,002
Other Sources Professional Radiation Exposure No 0
Packs of cigarettes smoked in a day No 0
Weapons test fallout Yes 1
House made of stone, brick or concrete Yes 7
Wear luminous wristwatch No 0
Smoke detector in the house No 0
Position of the house within 50m from a
Nuclear Power Plant
No 0
Position of the house within 50m from a Coal
Power Plat
No 0
Terrestrial Radon in the soil IA 1278,2
Total / / 1376,2
While inserting the elements of the table we have considered the “normal life” of an average
individual. This is why no medical procedures were included, or the fact that this ‘average
person’ does not wear a luminous wristwatch or does not live near a Nuclear Power Plant or
a Coal Power Plant. Furthermore, since smoking is not a common habit, in the United States,
it has not been considered.
Note that the elevation of the country (average) was considered, this is due to the fact that, as
the elevation rises, the population becomes more exposed to cosmic radiations.

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Moreover, the relative chart is:
While taking into account radon, the chart becomes:
0%
47%
2%
41%
2%
8%
Average Yearly Radiation Dose [mrem]
Medical Field Soil Cosmic Rays
Internal Radiation (Body) Sources Related to Flights Other Sources
0%
3% 0% 3%
0%
1%
93%
Average Yearly Radiation Dose [mrem]
Medical Field
Soil
Cosmic Rays
Internal Dose (Body)
Sources Related to Flights
Other Sources
Radon

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Considering that the estimated average yearly radiation dose per person in the United States
in approximately equal to 620 mrem (that is 6,2 mSv, since 1Sv = 100 Rem), we can see from
the table, how high this value is in Iowa. In fact, being 1376,2 mrem (13,76 mSv), it is more
than the double. Furthermore, the 93% of this value belongs to radon exposure (12,8 mSv).
Therefore, this is the main reason why this work focuses primarily on radon exposure in the
Iowa state. A comparison between the states is shown in the picture below, where zone 1 (red
spots) identifies counties with the highest indoor radon concentration; as we can see, Iowa’s
counties (circled in black) all belong to this zone.
Of course, the goal of the next sections is related to this map; in particular, we will try to
understand why these levels are so high in Iowa. But before doing so, we need to understand
what kind of soils have the highest radon concentration, how the radon moves through the soil
toward the surface (related to the type of soil and to radon’s characteristics) and what
conditions promote radon leakage. This shall be the objective of the next chapter.

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6. The Geology of Radon
We have already talked about how uranium (from now on we shall refer to 238
U simply as
uranium, unless specified otherwise) can be found in the soil, being present in most types of
rocks. The decay of uranium gives rise indirectly to radium and radon, since these
radionuclides belong to his decay chain. We can thus associate radium (226
Ra unless specified
otherwise) and radon (222
Rn unless specified otherwise) presence in the soil to uranium
concentration. There is though a big difference between these elements, and this difference
determines the different mobility of these elements into the soil.
Now, while uranium and radium (when formed) are in the solid phase; radon, belonging to the
eighth group of the periodic table of elements, is a heavy noble gas. This way radon can move
more easily through the soil, with respect to uranium and radium. This is due not only to the
fact that it’s a gas, but being a noble gas means that all the electronic shells are completed, so
this element does not react (from a chemical point of view) at all, with the matter surrounding
it.
The mobility of radon atoms, though, does not depend only on his chemical characteristics. In
fact, the position, where the decay takes place, needs also to be taken into account. By this we
do not mean the depth in the soil where the nucleus radon is emitted (even thought his
concentration in air diminishes with depth since more atoms decay before reaching the surface)
but the position within the grain where the nucleus is emitted. Furthermore, it also depends on
soil porosity, permeability and eventual fractures. The figure below shows the principle
processes that take place when radon is emitted and starts moving toward the surface, through
the soil.

16
The radionuclides that belong to the primordial decay chains are unstable nuclei (except for
the last one), and they decay spontaneously in order to reach a more stable configuration.
Considering radium, his decay gives rise to a radon nucleus, an alpha particle and a certain
amount of energy. This energy is released in the form of kinetic energy of the emitted particles.
These particles, will move through the matter thanks to this surplus of energy, interacting with
the atomic electrons “surrounding them”, causing ionization and excitation of the atoms
composing the medium. Quotation marks refer to the fact that since the coulomb field
permeates the space, through which those particles move, and considering that the Coulomb
force tends to zero at infinite distances, even far away electrons interact with particles; of
course the force in that case would be very small). From a macroscopic point of view, this
energy is dissipated in heath.
Now, the decay through which radon is created is called a ‘two body process’, since two
particles are emitted (typical of alpha decay processes). In addition, in this kind of process the
energy is divided, between the two particles, accordingly to the inverse of their mass; so that
the alpha particle takes away most of the energy.
Moreover, supposing the nucleus (the one that is about to decay) still, before the collision, and
knowing that momentum has to be equal before and after the collision (even though it is not
properly a collision), the final momentum (after the collision) will be also zero (being the
initial momentum zero, since we imagined the nucleus stationary before the decay). Now, the
final momentum takes into account the algebrical sum of the momentum of the two particles;
being zero requires magnitudes to be equal and directions to be opposite. This means that the
two particles will be emitted in opposite directions. Of course, if the radium nucleus is located
at the center of the grain, when it decays, the kinetic energy of the radon nucleus will not be
enough for it to exit the grain; furthermore, since radon has a really low diffusion coefficient
in solids, it will probably remain trapped. However, if the decay takes place near the surface
of the grain, the radon will probably be expelled from it and end up in the gap between grains.
In this case, the remaining kinetic energy could lead radon into another grain, especially if air
is present between them. Moreover, if a sufficient quantity of water stands among the grains,
it could act as a moderator, and slow the radon down before it enters a new grain. What we
have described until now (except for the nuclear process description) is called ‘emanation’, it
is basically the process that radon atoms follow to leak out from grains. The subsequent step
is called ‘transport’ and refers to the movement of radon atoms through grains toward the
surface. In this case, air and water exchange places, since the upward movement of air supports
radon diffusion across the soil, while water slows it down. Considering this last process, it is
simple to understand that the easier air (or water, even though it more difficult for the liquid
phase to move across the soil) moves upward towards the atmosphere, the easier the radon will
leak out of the soil. Fractures in the soil for example will favor transport. The final process,
which radon atoms go through, is called ‘exhalation’. Exhalation of radon atoms transported
across the soil leaking into the atmosphere. The conclusions now, about what promotes radon
leakage, can be easily understood.

17
Referring to the soil’s characteristics:
▪ High Porosity enhances the probability of radon leakage, since it favors air’s
movement across the terrain;
▪ Permeability, which can be defined as the property of soils to allow liquid phase
substances to move through them, also enhances radon movement even though high
permeability levels combined with high quantity of water (rainy regions) can reduce
radon exit.
We can thus deduce that coarse grained soils characterized by large gaps between grains (or
easily fractured soils) let radon escape more easily than fine grained soils. Enhancing this
way radon concentration in the atmosphere.
Now, more easily, we can understand why high concentrations of radium (uranium) in the
soil does not necessary imply high concentrations of radon in the atmosphere; and
consequently why houses built on soils characterized by high levels of uranium may in fact
have low concentrations of radon if the soil has low porosity and low permeability.
7. Why Are Radon Levels so High in Iowa?
As widely anticipated, Iowa has the highest levels of radon indoor; in fact, something like
71,6% of the houses built on the Iowa land present levels of radon far above the EPA’s action
level. This level is taken to be equal to 4 pCi/L (= 148 Bq/m3
), that is 4 pCi of radon per liter
of air. In the United States, the average radon concentration (indoor) is equal to 1,3 pCi/L,
while Iowa presents levels as high as 8,5 pCi/L (average value). To get the idea of how high
this levels is, we need to see what ‘pCi/L’ means. It is know that the pCi (picocurie) quantifies
the radioactivity of a certain radionuclide; in particular, 1 pCi corresponds to the decay of
nearly two radionuclides per minute. So 4 pCi/L implies that in a closed environment (could
be an entire house or a single room) we have, as already stated, 4 pCi of radon atoms per liter
of air. This means we have approximately 8/9 atoms of radon that decay every minute in every
liter of air present in the house (if the value has been measured in a home). Imagining now that
our house has a surface of about hundred square meters, there will be something like 2 millions
of radon atoms that decay every minute! Remember though that we have been referring to the
EPA action level; average radon levels in Iowa are doubled, and so is the result. This can help
understand the magnitude of the situation.

18
We shall concentrate now on understanding why these levels are so significantly high in Iowa.
This depends on several factors. Let us see some of them:
▪ Soil’s characteristics like levels of porosity and permeability, and the presence of
fractures (and caves eventually);
▪ Rainfall rates, and eventually snow rates could be taken into account;
▪ How houses have been built;
We shall concentrate only on the first two points, assuming that radon levels indoor are quite
independent on how houses were built. Proceeding with this evaluation, we shall first see what
kind of different soils compose the Iowa land, then we will try to find a correlation between
these soils and uranium concentrations inside them and finally we shall concentrate on factors
that can enhance/inhibit radon leak out of the soil.
7.1. Different Types of Soils
In this paragraph, we shall see the difference between the rocks composing the soil. After that,
we will proceed analyzing Iowa’s land, in order to understand if uranium concentration in the
soil are effectively high (since we know that high levels of uranium in the soil does not
necessary imply high indoor concentrations, as well low uranium levels do not imply low
indoor concentrations).
Looking at the earth’s cross section, we shall see a series of concentric shells; these shells are
characterized by different composition (in terms of materials) and therefore different density.
The last shell (i.e. the one closest to the surface) is called ‘crust’. The crust is mainly composed
by rocks, which are nothing more than an aggregate of one or more different minerals. Now,
rocks can be divided into three families, based on the particular lithogenic process they went
through (certain type of process that gave rise to a certain type of rock).
These families are:
➢ Magmatic rocks (also called igneous rocks): basically, these rocks consist of an
aggregate of minerals deriving from the crystallization of magma due to his gradual
reduction in temperature as it moves through earth;
➢ Sedimentary rocks: due to the erosion and subsequent transport of rocky materials
belonging to the earth’s surface;
➢ Metamorphic rocks: derive from the transformation of the previous two kinds of rocks,
when they undergo processes different from the ones that originated them.

19
Moving on to Iowa now, we can recognize three different layers, into which the soil could be
divided. Magmatic rocks (e.g. granites) compose the deepest among the three. These rocks can
also be found in the surface, in the form of boulders and pebbles, but to a lesser extent. The
middle layers is mostly composed by sedimentary rocks, such as limestones, sandstones,
shales, dolostones and siltstones. While the upper layer is mainly glacial till. As seen in the
first chapters, uranium can be found almost in every rocks (and consequently in the soil
composed by these rocks); but of course, the concentration may vary from rock to rock. The
average concentration of uranium in rocks is approximately equal to 3ppm; however, several
rocks may contain up to 100 ppm of uranium. This is the case of volcanic rocks, granites,
sedimentary rocks containing phosphates and metamorphic rocks derived from the latters.
Granite for example, which is an intrusive igneous rock, is the most common rock (as well as
the one that solidifies at a lower temperature). Before reaching the solid phase, this “rock”
(also thanks to his low density) moves upward through the crust and, due to geochemical
processes, it enriches itself with different elements, among which we find uranium. Of course,
the concentrations we are talking about are not enough, for these rocks, to be considered from
an industrial point of view; nonetheless, they still could represent a health hazard. The presence
of granites in Iowa is mostly due to the movement of glaciers from the Canadian mountains;
in fact, these glaciers have brought with them large quantities of rocks and minerals. Therefore,
after the glaciers melted down, all these rocks got exposed to the surface and became part of
the soil.
The middle layer, as stated, is the one composed by sedimentary rocks; in particular, those
enriched with phosphates. In the case of Iowa, mostly limestones and mudrocks (e.g.
claystone, shales and siltstones), massively present into the soil. The reason why these rocks
have high uranium concentrations can be understood analyzing their process of formation.
Apatite is the main mineral composing these rocks and it is also one of the major constituent
of the skeleton of living beings (bones). Now, the processes that can give rise to the apatite
mineral could be biogenic or not. The mineral could be found in marine animal’s carcasses on
the ocean bed, or could be due to hydrothermal marine activity. Now, we know that based on
chemical properties, some radionuclides present a certain degree of tropism (affinity) towards
one or more organs (or tissue). In this case, the affinity is between uranium and bones; being
the latter, a tissue characterizes by really low rates of biological exchange, the uranium, once
sat it will probably remain there. Considering the apatite mineral now, what happens is that
uranium gets taken instead of calcium, and it settles there (remaining trapped into the marine
animal’s carcasses). The reason why these rocks (and this mineral) are widely present through
out Iowa is to be related to the period preceding the last ice age, where Iowa was covered by
the ocean.

20
In conclusion, this section showed that, as we expected, uranium concentrations in rocks, in
the Iowa state, are effectively high; but, as we said, this is not the only reason that makes the
indoor levels so high. In fact, we shall now concentrate on the soil’s characteristics (such as
porosity and permeability), taking into account rainfall rates during the year and average
temperatures.
7.2. Landform Regions in Iowa
Knowing the multiplicity of conditions that could enhance radon leakage out of soil, we shall
focus only on those that can be considered of greater importance (have a greater influence on
radon emission). Those are:
▪ Soil composition;
▪ Soil porosity levels;
▪ Soil permeability rates;
▪ Rainfall rate.
Of course, in this section we will focus on the individual counties and not on Iowa as a whole,
since the difference is quite big throughout the territory. We may then identify seven, so called,
‘landform regions’ based on the geological history each region went through. These regions
can be seen from the figure below.

21
Moreover, the territory can also be divided based on the permeability rate, expressed in in/h
(i.e. inches per hour), of the soil. This partition gives rise to six regions. We may now correlate
the regions divided based on permeability rates with the ones divided by the geological history,
to obtain:
• Zone 1: has a moderate permeability rate (from 0,9 to 1,21 in/h) and covers the
‘Northwest Iowa Plains’ region;
• Zone 2: characterized by high permeability rates (from 1,21 to 14,4 in/h) and covers
‘Des Moines Lobe’, Iowan Surface’ and the ‘Paleozoic Plateau’ regions;
• Zone 3: with moderate permeability rates (from 0,9 to 1,28 in/h) and covers the
northwest part of ‘Southern Iowa Drift Plain’ and south part of ‘Mississippi Alluvial
Plain’;
• Zone 4: which covers completely the ‘Loess Hills’ and Missouri Alluvial Plains’ regions
and the west part of the ‘Southern Iowa Drift Plain’ region. This zone is characterized
by medium/high permeability rates (from 1,21 to 1,28 in/h);
• Zone 5: covers the middle-west part of the ‘Southern Iowa Drift Plain’ and has low
permeability rates (from 0,66 to 0,9 in/h);
• Zone 6: covers the southeast part of the ‘Southern Iowa Drift Plain’ region and is
characterized by really low permeability rates (from 0 to 0,66 in/h).
The picture below shows the six zones (painted with different colors) in which the territory
has been divided, based on the permeability rate.

22
Let us be a little more specific now, and focus on each region.
Zone 1 is characterized by the highest indoor radon
concentrations, and it belongs, in part, to the Northwest Iowa
Plains. Rainfall rates on this territory are extremely low, this
inhibits fall out (onto the soil’s surface) of the radon decay
products (e.g. polonium), present in the atmosphere. This
enhances their concentration in the air. Sandstones and shales,
as primary and secondary rocks respectively, mainly compose
the soil. These are high porous rocks, and this as we have
largely seen, favors radon’s leakage.
Zone 2, which comprises Des Moines Lobe, Iowan Surface and Paleozoic Plateau, is
characterized by levels of radon (we will always refer to indoor radon concentrations, unless
otherwise specified) that decrease as we move from Des Moines Lobe (center part of Iowa)
to Paleozoic Plateau (eastern part of Iowa). However, rainfall rates increase in the same
direction (yearly average value). Permeability rates are also pretty high in this region.
Combining these two characteristics (increasing rainfall rates and high permeability) lowers
radon decay product’s concentration in the air (with respect to zone 1).
Soil’s composition varies a lot throughout this region; however, a primary and a secondary
rock could still be identified. These are, respectively, limestone and dolostone (low porous
rocks). The low porosity of these rocks is another factor that diminishes radon concentration,
since it reduces the percentage of the atoms that leak out of the terrain.
Zone 3 has the same permeability rate of region 1, but of course soil’s composition and
rainfall rates are quite different. In particular, dolostone is the primary rock, while limestone
is the secondary. We have already seen how these rocks have very little porosity (partly
because these are fine-grained rocks). Rainfall rates are extremely high; so in the end, radon
concentration is here lower with respect to zone 1.

23
Moving on to zone 4, we can see how permeability rates are extremely high while rainfall
rates increase as we proceed from north to south. Though primary rock, just like zone 2, is
limestone (low porosity); being shale the secondary rock (instead of dolostone of zone 2) and
being rainfall rates low, causes radon levels to be higher than the one present in the zone 2.
In fact, lower rainfall rates together with high permeability causes the water to flow through
the soil, increasing the number of radon atoms that remain “trapped” in the gaps between
grains (instead of getting stuck in the grains).
Zone 5 presents a very different soil composition from place to place, this makes it very hard
to analyze (as a whole). Therefore, in this case, we will proceed on comparing the single
counties:
• The Union County and the Taylor County happen to have the same soil composition
(therefore same porosity), same rainfall rates and consequently same radon levels.
Since the regions have been divided based on the permeability rate, this will be the
same throughout each zone; this is the reason why we did not consider it.
• The Madison and Adams Counties have the same rainfall rates. However, the
Madison County has siltstone as secondary rock (higher porosity than limestone,
secondary rock of the Adams County). This leads to higher radon levels in the
Madison County.
• The Guthrie County has really high radon levels; this is probably due to the high
porosity of its soil (sandstone and shale). These levels are lower than the ones found
in the Adair County (highest levels in the region), even though primary rock is
limestone. This is probably related to the type of primary rock composing the terrain
of the Guthrie County. In fact, combining high rainfall rates together with the fact that
sandstone soils have high water seepage, leads to high levels of water remaining
trapped into the soil, diminishing radon leakages.
Finally zone 6, which has the lowest permeability and the highest rainfall rates. The soil
composition also varies greatly in this region. It goes from sandstone to shale and from
limestone to dolostone (as primary and secondary rocks respectively). The formers
characterized by higher porosity than the latters are. However, being the soil impermeable,
the water tends to stratify onto the soil’s surface, inhibiting radon exit and consequently
reducing its concentration in the air.
A chart, at the end of this work (appendix A), presents the radon levels for each county
(Iowa). The different colors of the bars, for every county, represent a different radon
concentration, while the length of the bars takes into account the percentage of that county
characterized by that particular indoor concentration (average values).

24
8. Why is Radon Considered so Dangerous?
The preceding chapters, as anticipated, were based on trying to explain why the choice has
fallen upon radon and Iowa. We have seen how 222
Rn represents the major health hazard, with
respect to the other isotopes. Than we have brought our attention towards Iowa, and analyzing
its geology, we have come to understand why indoor radon levels are so high. What we have
not explained though, is why radon is considered so dangerous for human health. This is to be
found in the chemical-nuclear characteristics of his decay products.
As we know, the radon element belongs to the eighth group of the periodic table of elements,
which means it is a noble gas. Being a noble gas implies that all of his electronic shells are
completed, so it is not a chemical reactive element.
Now, the irradiation caused by charged and non-charged particles, may come both from the
outside (which we refer to as external irradiation) or from the inside (internal irradiation), with
respect to human body. Of course, we can even have both. Since the particles emitted by radon
and its progeny are mostly alpha particles, they are not of great interest from the external
irradiation point of view. In fact, alpha particles, being heavy charged particles, tend to interact
more (with respect to electrons for example), therefore losing more energy with the matter
surrounding them, i.e. atomic electrons. This can be easily seen considering the so called
‘Stopping Power’:
𝑆 𝑒𝑙 = −
𝑑𝐸
𝑑𝑥
=
2𝜋𝑚𝑒2
𝑚0
[
(𝑧𝑒)2
𝑚𝑣2 2⁄
] 𝑁𝐵𝑍
Where ‘m’ is the interacting particle’s mass, ‘m0’ is the electronic mass (since the particles
interacts with atomic electrons mostly). While ‘B’ is a factor that takes into account the
ionizing potential of the medium crossed by the incident particles, ‘N’ represents its atomic
density and ‘Z’ its atomic number so that their product gives us the total number of electrons
present per unit volume. Moving on to the term between brackets, the numerator represents
the square of the total charge of the incident particle, the denominator is its kinetic energy.
Therefore, this physical quantity quantifies the loss of energy (minus sign) per unit path length.
Of course the interactions we are talking about are excitation and ionization processes. These
imply a deformation of the atomic structure of the atoms they interact with (i.e. inelastic
collisions). In fact, the subscript of the letter ‘S’ does not stand for ‘elastic’, but for ‘electronic’,
meaning the targets of the interaction are the atomic electrons.
We may also consider the energy lost due to Bremsstrahlung emission, the energy related to
this process though is really small if compared for example to the one emitted by the electrons.

25
Moreover, knowing that the power irradiated by Bremsstrahlung emission (Larmor formula)
is proportional to:
𝑝 ~ (𝑞𝑎)2
= (𝑧𝑒
𝐹
𝑚
)
2
Considering now, an alpha particle and an electron on which the same force (Coulomb) is
acting, the ratio between them is:
𝑝 𝛼
𝑝 𝑒−
= (
𝑧 𝛼
𝑚 𝛼
)
2
(𝑚 𝑒−)2
≅ (
2𝑚 𝑒−
4𝑚 𝑝
)
2
≈ 14 ∗ 10−6
𝑝 𝑒− ≈ (14 ∗ 106)𝑝 𝛼
We can easily see why the power emitted by alpha particles due to Bremsstrahlung may be
neglected, with respect to one emitted by electrons.
Returning now to the electronic stopping power and supposing an alpha particle and an
electron are interacting with the same medium and have the same energy (this implies ‘N’, ‘B’
and ‘Z’ to be equal), being 𝑆 𝑒𝑙~(𝑧𝑒)2
shows the greater loss of energy per unit length of the
alpha particle with respect to the electron.
Now, the tissue that composes our skin may be divided into layers. Of these layers, the outer
is mainly composed by dead cells, while the inner is made up by stem cells (undifferentiated
cells capable of reproducing themselves). The damage induced to these cells is obviously more
dangerous than the one caused to dead cells. The thing is, alpha particles emitted by natural
radionuclides (alpha emitters) do not reach this layer (stem cells), when interacting from the
outside. Having a short range, the dead cell’s layer stops them.
The situation is different considering an internal irradiation. This can though take place in
many ways:
• Through the respiratory system;
• Through the gastrointestinal system;
• Through wounds;
• Through injection or percutaneous absorption (“direct” way).
Radon for example, penetrates the body using the first way (even though it may enter also
using the second). But in this case, radon itself “is not the problem” since it is a non-reactive
element and has a pretty long half-life, with respect to his decay products (to be noted that in
case of activity incorporation, other than the physical half-life, also the biological one has to
be taken into account). This means that after being inhaled, the radon will probably exit the
body without forming any compounds. The real problem comes with its progeny, in fact these
radionuclides interact thanks to electrostatic processes with the matter surrounding them. In a
closed environment for example, they tend to be attached to dust particles (and walls), being
easily inhaled. This of course does not happen with the ones attached to the walls.

26
Now, the length traveled by the dust (to which the progeny is attached) through our body,
depends on its granulometry (dimensions). Coarse dust particles will probably be trapped by
the nose mucus and remain there until it is removed (by forced removal for example). Fine
dust particles however, will probably cross the nose and remain stuck into the mucus generated
by the cells composing the tissue of the bronchi (bronchial tissue, whose cross section is shown
in the picture below).
Among all of the radon’s decay products, those that interest us the most are the alpha emitters.
In this case, the energy of these particles is such that they interact with the stem cells of the
bronchial tissue. Moreover, since heavy charged particles tend to release a greater deal of
energy at the end of their range (Bragg’s peak), the damage in this case (end of range coincides
with the position of stem cells) will be even more. In fact, in this case the depth (with respect
to the “surface”, where air flows) of the stem cell’s layer is approximately 40/50μm. Now,
supposing that the composition of the bronchial tissue is equivalent to the one of the adipose
tissue, let us see what distance (i.e. range) the alpha particles, emitted by some of the radon
decay chain, cover (and if they reach the stem cells). We shall consider the 5,489 MeV alpha
particle emitted by radon, and the 6,002 alpha particle emitted by polonium. Being bismuth
and lead beta emitters, we will not consider them; the electrons in fact will reach for sure the
stem cell’s layer.

27
For the equivalent adipose tissue, a density of ρ = 9,20000E-01 g/cm3
and an average excitation
energy of w = 63,2 eV have been chosen (ICRP). The range values have been evaluated using
a program called ‘aStar’. Two different values of range are shown:
- Projected Range: which is the thickness of the absorbing medium crossed by the
particles; it simply takes into account the distance lapsing from the point through which
the particle enters the medium and the point where it gets absorbed;
- CSDA Range: usually bigger than the first, is a better approximation of the mean length
traveled by the particles.
Both of these quantities shall be presented, for completeness:
• Eα = 5,48948 MeV; Rp =4,001E-03 g/cm2
; RCSDA =4,016E-03 g/cm2
;
• Eα = 6,00235 MeV; Rp = 4,608E-03 g/cm2
; RCSDA = 4,623E-03 g/cm2
.
It is also important to note how the results are expressed in terms of g/cm2
, even though range
identifies a length (i.e. ‘cm’). This is due to the fact that these values have been calculated per unit
of density. Since range in materials having the same chemical structure but different densities
varies, usually a mean range is evaluated for a specified substance, making the calculations less
laborious. This way, if the range needs to be evaluated for a specified density (of a certain
substance), it only takes a division (between range and density) to get the results. The “real” values
are then:
• Eα = 5,48948 MeV; Rp =4,34E-03 cm; RCSDA =4,365E-03 cm;
• Eα = 6,00235 MeV; Rp = 5,008E-03 cm; RCSDA = 5,025E-03 cm.
This shows that the range of the alpha particles, of the isotopes considered, are comparable
with the depth at which stem cells can be found (relatively to the bronchial tissue). In this case,
the alpha particle could cause a double strand break into the cell. At this point, the cell could
die or reproduce itself. If it undergoes reproduction, the new cell (with the damaged DNA)
could die or again reproduce. If the reproduction process continues, it could lead to the
development of a carcinoma (of course the fact that this process develops or not, depends also
on the biology of the individual). The total probability for this event is equal to the product of
the single probabilities, being the events related to one another. These are stochastic events,
described by a stochastic risk. In these cases, higher frequencies of the leading events lead to
a higher risk. Of course, the risk increases with the exposure (not the physical quantity) caused,
for example, by higher indoor radon levels.

28
Returning now to the physical phenomena controlling radon leakage, we have seen how and
why the radon moves through the soil (existence of a pressure gradient). Of course radon levels
will be higher in closed environments since the pressure is lower (due for example to higher
temperatures inside the building); and, being heavier than air, it stratifies in the lower part of
rooms (mostly basements if there are any, since they are closer to the soil). Furthermore,
supposing that a person sleeps, on the average, 7h per day, for approximately 1/3 of the day
the radon incorporation increases since we are closer to the floor.
The absorbed doses we are referring to are of course extremely low, but protracted for long
periods of time. As a matter of fact, at first it has not been simple to correlate causes and
effects. Nevertheless, we shall discuss it in the next chapter.
9. Correlation Between Causes and Effects
After World War II, in particular after the bombings of Hiroshima and Nagasaki, it was noted
that the number of cases of cancer had incredibly increased. Therefore a series of studies were
conducted to better understand the correlation between stochastic risk (i.e. the probability of
the occurrence of heritable effects differed in time) and the dose received (we are talking about
effective dose, referred to the body as a whole). The data achieved through these studies,
showed that this correlation was linear (higher doses led to higher risks). Nevertheless, of
course, the dose received because of the bombing was quite high and the number of subjects
was large as well, so a relation between causes and effects, in this case, was easily found.
However, in everyday life, the doses received by the population are quite low and of course of
more importance (considering the two bombings as rare events). Therefore, this brought up
the issue of finding a relation considering low doses. Relation that could not be found in terms
of epidemiological studies, since the subjects that had to be analyzed were too many. In fact,
the number of noxae patogene that could cause heritable effects is quite large, and this makes
it difficult to correlate the arise of a carcinoma (heritable effect differed in time) due to ionizing
radiations instead of another cause. Consider that to get results statistically significant and
without any informations, nearly 30 samples have to be considered, each with a least 105
persons, that makes 3*106
persons to analyze for the whole life, physically impossible!
Two models were then considered:
• One implying a threshold, below which the risk was practically zero;
• One that maintained linearity, i.e. with no threshold, based on a linear extrapolation of
the high dose’s trend.

29
The ICRP chose the second model, called Linear No-threshold (LNT). The figure below (left)
shows the two models. Of course, choosing the LNT model means that neither the natural
background can be excluded, since there is no threshold. Nonetheless, there are values below
which there no detectable excesses in the rise of heritable effects in the population, as shown
in the table below (right).
This led to the establishment of limit values for the effective dose received by a member of
the population. In Italy for example, this limit was set to 1 mSv/y, considering single
individuals. At these levels, the frequency of interaction is really low, we are talking about
something like an interaction per year per cell. Now, recalling the part in which we talked
about the effects of ionizing radiations, and how the most dangerous were related to double
strand breaks; considering the limit described above, the probability related to this process is
far below other damages. The table below shows the comparison.
Of course, what has been said about the correlation between risk and does also applies for
radon and its progeny. In fact while it was quite obvious that high concentrations of radon
could cause cancer, for low levels (e.g. in homes) the situation was not yet clear. Before
proceeding let’s stop and focus on epidemiological studies, since we have “brought it to
surface” previously in the chapter.

30
10. Epidemiology and Epidemiological Investigations
Epidemiology can be defined as the branch of medicine that analyzes the frequency through
which certain diseases occur in a population, their distribution and what causes them.
Considering epidemiological studies, the attention is focused on very large groups of people,
and not on individuals. Of course the number of subjects needs to be large in order to better
understand what factors contributed to the development of the particular disease. The subjects
in study comprehend individuals in which the disease developed and subjects in which it did
not.
The first epidemiological investigations about radon were done with miners from all over the
world. In these cases, high radon concentrations were due not only to high levels of uranium
in the soils (since these were uranium mines), but also because of thermal zones near the mine
and eventually faults, that may increase radon leakage. Of course, we are talking about
underground mines. These investigations showed an excess of cases of lung cancers, compared
to what the expectations were (i.e. considering individuals not exposed to the same conditions).
Being the studies conducted on miners of easier interpretation (mostly due to the lack of other
diseases that could cause lung cancer, in mines), it was then decided to carry out more studies,
but this time on miners exposed to levels (of radon) comparable with the ones present in homes
(on the average). Even in this case, a linear correlation between risk and exposure was found.
Of course, comprehensive analyses had to take into account data derived from studies taken
on individuals effectively exposed to radon in houses. Nonetheless, over the years a large
number of studies were made; most of which confirmed the results of the mine studies (others
were not taken on a sufficient number of individuals to be considered statistically reasonable).
Anyway, to consider an epidemiological investigation ‘reasonable’ (on how close result can
represent reality), it is necessary to have data even older than the one taken at the moment of
the study, or even have the possibility to rebuild it from the past. This of course led to
complications, which means uncertainty on the results, mostly due to the fact that lots of homes
presented radon levels way different from the ones recorded at the time and, in some cases,
the buildings did not even exist anymore. Even though the characteristics needed, for an
epidemiological study, to be considered statistically reasonable are quite a lot, it is still possible
to identify some of them:
➢ Data achieved has to come from studies protracted for long periods of time (i.e.
extended exposures);
➢ Large number of subjects analyzed;
➢ Since the studies are related to radon concentration in houses, it is necessary to consider
individuals that usually spend more time at home;
➢ Subjects analyzed must have lived in the same home for a long period of time;
➢ Existence of a register where data, related to individuals that have developed lung
cancer over the years, is collected.

31
The National Institute of Environmental Health Sciences (NIEHS), in Iowa, has taken a study
of this kind (on a five-year time). The subjects of this study were mostly women (smokers and
not), since women, on the average, tend to spend more time at home and are less exposed to
other noxae patogene related to lung cancer. Furthermore, women in Iowa tend to move less;
the individuals in fact, had been living in the same house for at least 20 years. All these factors
have made the investigation simpler. As largely seen in the preceding chapters, Iowa presents
the highest indoor radon concentrations among the United States; moreover, an excellent
Surveillance, Epidemiology, and End Results Program exist, made by the National Cancer
Institute. The study conclusions were the following:
“The risk estimates obtained in this study suggest that cumulative [total] radon exposure in
the residential environment is significantly associated with lung cancer risk.”
In complete agreement to what EPA stated. In particular, the investigation has shown that, on
the average, an exposure equivalent to the EPA’s action level (4 pCi/L), ‘carried out ’ for 15
years, increases the risk of getting lung cancer by 50%.
11. Laws and Regulations
11.1. Italy
The investigations described in the preceding chapter, brought up the necessity to establish
concentration levels, above which it would have been necessary to intervene.
The value previously described of 1 mSv/y is the one imposed by the Italian legislation for
individuals of the population. That value applies only for individuals, meaning that in a single
year the single member of the population cannot take more than 1 mSv (effective dose). Now,
those limits, imposed by the Italian law, are indeed born as recommendations established by
the ICRP (whose job is to issue recommendations in the radiation protection’s field). Once a
recommendation is published, an institution takes them and revises them in order to publish,
in return, some sort of ‘directives’. In this case, the institution that is responsible for this is
EURATOM. These directives are usually written in general terms; then, taken by the
individual legislations they become more specific and ‘appropriate’ for a certain situation. For
example, the 96/29 EURATOM directive sets a dose limit (effective dose for professional
exposure) of 100 mSv in a consecutive period of 5 years, with no more than 50 mSv/y. Every
legislation sets its own yearly limit, the Italian laws, for example, sets this limit equal to 20
mSv/y. Anyway, this directive refers to the publication number 60 of the ICRP of the 1990;
Italy followed it with the ‘D.Lgs #230 del 1995 with modification and integrations’.

32
However, in 2007 another ICRP’s article was published (publication number 103 of 2007), to
which an EURATOM directive followed. Italy, in this case, has a 5 years’ time to comply with
this new directive (up until February 2019).
11.2. United States of America
The situation is though quite different in the United States, since in the 1970 became
operational the USEPA (United States Environmental Protection Agency). The agency’s job
was to develop regulations in order to protect the population and the environment from the
negative effects of ionizing radiations and chemical substances (the former do not comprehend
radiations emitted by electrical devices, such as cellphones). However, together with these
regulations, the agency also develops technical guides used by state and federal agencies to
develop standards. Quite the same thing happens in Italy (Europe). As we stated upstream, we
have ICRP’s recommendations, these are then “transformed” by EURATOM into directives
and finally by the individual national legislations into laws. Together with these laws, come
operative guides that are developed by national authorities (ISPRA in the case of Italy). These
guides are the ones exploited by the “radiation user”.
Let us focus now on how these regulations (related to radon of course) were developed, taking
into account different agencies, following a chronological order.
Among the first regulations related to radon exposure, there was the one established by the
National Council on Radiation Protection & Measurements (NCRP 1984c). This regulation
presented an upper limit for radon exposure in a year time. This was considered as the
maximum risk that could be tolerated, since an exposure equal to this limit would imply a 2%
excess of deaths caused by lung cancer. This upper limit was set to 2 WLM (equivalent to 8/10
pCi/L, if the equilibrium ratio is set equal to 0,4 or 0,5). This ‘action level’ represents the upper
limit of exposure above which it is necessary to operate in order to reduce the concentration.
Usually the “operations”, considering radon in buildings, are changes in the building’s
structure in order to decrease the percentage of radon that enters the house, or the building in
general. Of course the risk still exist even below the action level, this is why the NCRP
recommends a mitigation even at these levels, in order to reduce even more the risk.
At the same time, EPA was recommending an action level of 150 Bq/m3
(4pCi/L). Being an
‘action level’, this value could also be considered as an upper limit above which mitigation
processes were necessary. This recommended value, in particular, had been developed from a
guideline directed to houses built near uranium factories. Some of them were:
▪ If concentrations exceed the natural background by a value equal to 0,05 WL, it is
necessary to take action. This level corresponds to 10/12 pCi/L depending on the
equilibrium ratio, of the progeny, chosen (if 0,4 or 0,5).
▪ Actions are recommended, in order to reduce concentrations, if these exceed the natural
background by a value taken between 0,05 and 0,01 WL;
▪ No action is needed (indicated) if concentrations are below 0,01 WL.

33
It is curious to note how this guidelines change with the decreasing concentrations, passing
from ‘necessary actions’, to ‘recommended action’ and finally to ‘no action need’. In fact, this
is pretty much how these regulations work. Above the action level mitigation processes are
strongly recommended, being the risk very high; while below certain levels, even though the
risk could still not be considered zero, it is related to very low probabilities.
Over the time, EPA has still been recommending the same action level (i.e. 150 Bq/m3
). In
fact, this value was considered as ‘technologically reasonable’ in most of the buildings; since
houses differ from one another, it is not possible to reach (with mitigation systems) the same
levels for every home. For example, at present, if the concentration value is between 75 Bq/m3
and 150 Bq/m3
(2 – 4 pCi/L), mitigation actions are recommended if it is possible to reduce
even more the level of concentration.
The action level for houses, suggested by ICRP, are set for example between 500 and 1500
Bq/m3
(publication number 65 of 1993), while the 96/29 EURATOM directive established a
lower range of 500 and 1000 Bq/m3
. Of course, the action value varies according to the “type”
of building. In particular, this level is set to 400 Bq/m3
considering houses that have already
been built, and 200 Bq/m3
for homes on the verge of being constructed. The table below shows
some characteristic values:
Of course, not all the countries were considered, but only the most particular. In India, for
example, no value is set for new buildings (or the value exist but is unknown). The values
established by Italy correspond to the ones recommended by ICRP and then ‘modified’ by
EURATOM. The Netherlands have also been considered, since their action level is extremely
low; this of course is not due to lack of administration. In fact, it is important to note that the
average indoor radon concentration in the country is small (29 Bq/m3
), if compared to others.
It is though necessary to specify that these reference levels can be lowered by private
institutions. In the United States for example, some lending institutions set these levels below
the one established by EPA, for homebuyers that apply for loans.
We have seen so far what kind of agencies EPA and ICRP are, and what is their job; with
regard to NCRP, this institution can be considered as the US equivalent of the ICRP.
When first it was set up, its job was to represent all the US organizations related to the radiation
protection’s field. Therefore, this institution establishes recommendations and guidelines
(developed thanks to research) related to the radiation protection, in analogy with ICRP.
Country Reference
(action) level
for existing
buildings
[Bq/m3
]
Upper bound for
new buildings
[Bq/m3
]
Year set
India 150 / /
Italy 400 200 /
Netherlands 20 20 1994
USA 150 150 1994

34
12. Concerning EPA
Let us spend now some words on the agency whose job is to protect people and the
environment in the United States, i.e. EPA. Moreover, this is carried out with the help of
educational programs, partnerships and last but not least through the development of the so
called regulations. This authority, that has been given to this agency, was provided by the
Congress (through which all the American laws have to pass). In particular, EPA’s duty is to
make sure that all the laws concerning the protection of human health and the environment are
being followed, and this is done thanks to the development and enforcement of regulations. Of
course these regulations (mandatory requirements) are not only directed to individuals, but
also to state and local governments. Furthermore, these directives, as already stated, are not
optional; instead, they refer to something that is required. Let us concentrate now on these
regulations, in particular we shall proceed on describing how they are created and successively
published in the Code. After that, we will discuss the structure of the EPA organization and
focus on the area that deals with radiation protection.
12.1. The Making of Regulations
Before proceeding with the description on how regulations are developed, we will first try to
understand how laws are created in the United States.
Everything starts from a member of the Congress, which proposes what is called a ‘bill’. This
bill is a document that goes through different processes, and if approved and all becomes a
law. Now, being the bill proposed by a member of the congress (belonging to a certain party),
before getting into the hands of the president, it has to be approved by both parties of the
congress. After that, the bill goes to the president that can either approve it or vetoed it. If
approved, the bill becomes a ‘statute’ or act. Once passed, the statute needs to be standardized
and published on the US Code. All the US laws are published on this Code divided by the area
to which they apply. At this point the statute (i.e. the law) is official. Nonetheless, laws usually
refer to general situations and therefore are free of details, which can be useful for individuals
in order to follow them. This is why regulations are created, since they present the details
needed to apply laws in specific situations.
Of course, different regulations refer to different statutes, that is why we will not refer to any
particular regulation, but shall proceed on describing a sort of general process.
In analogy to what happens to the laws, when passing from a bill to a statute and becoming a
law, the regulations too are “transformed” into two documents, before becoming official.
However, in this particular case the two documents are called respectively ‘Notice of Proposed
Rulemaking’ (NPRM) and ‘Final Rule’. The final rule is the one that, in the end, gets codified
into the Code of Federal Regulation, in short CFR. Let us see now how the proposed document
becomes official. The first step is of course to see if the regulation is actually needed at all. If
it happens to be so, the document is then proposed and what we obtain is the NPRM.

35
The proposed document is then published in the Federal Register (accessible to the public), in
order to make sure that people may see it and eventually comment it. The comments left by
people are then analyzed and the document is reviewed and modified, eventually, and then
finally released. This document, which will be too published onto the Federal Register, is
named Final Rule.
Now, just as the laws are codified into the US Code, the same thing happens to the Final Rule.
In fact, in order to complete the process, this document has to be codified in the CFR. The
CFR collects all the regulations and is updated yearly; it is divided into 50 volumes called
‘titles’. Every title refers to a particular area, the title 40 for example, is the one related to the
environment.
This is essentially the process that leads to the publication of a regulation, a document
containing all the details needed in order to follow a certain law (to which the regulation refers
to). This is the reason why the EPA is a ‘regulatory agency’. Therefore, all the laws and
executive orders that apply for radiation protection are “controlled” by this agency. All EPA
for example, administrates the CAA (clean air act), the CWA (clean water act) and the AEA
(atomic energy act).
In particular, the Atomic Energy Act (AEA) gave rise to the Atomic Energy Commission
(AEC), in order to promote the pacific use of atomic energy in various fields. The AEA then
passed under the control of the Nuclear Regulatory Commission (NRC), after the AEC had
been abolished. The NRC job was to develop guidelines and regulations in the nuclear reactor
and material security field.
There was also a large number of areas, in the nuclear field, controlled by the AEC. Of course,
among these there was the area related to the environmental protection. However, when EPA
was created, this area passed under its control; and so did the authority of developing and
enforcing regulations.
12.2. EPA’s organization
We will now concentrate on the EPA’s
organization, in order to understand what area
deals with the radon problem.
Now, as we already said, the EPA
administration covers entirely the United
States. Being a very large territory, it was
necessary to divided into zones so that each
one of them could be regulated by a specific
office. In particular, the territory was divided
into 10 regions, as shown in the figure below.
Iowa for example belongs to region number 7,
and so do Kansas, Nebraska and Missouri.

36
Each of these regions has a certain number of offices, each of which deals with a different
issue. For example there is the OARM (office of administration and resources management)
or, in the case of radon, the OAR (office of air and radiation). This office in particular deals
(through regulations and national programs) with problems related to air pollution and
radiation exposure; for example, indoor and outdoor air quality, radiation protection and radon.
This office, besides administrating laws such as the CAA and AEC seen before, is made by a
number of subsections that deal with more specific issues. Among these, we have the OAQPS
(office of air quality planning and standards), the OAP (office of atmospheric programs), the
OTAQ (office of transportation and air quality) and the ORIA (office of radiation and indoor
air). The latter substantially deals with air quality and the protection of the environment and
the people from negative effects of ionizing radiations. Furthermore. This particular section
develops standards and programs in order to protect the individuals and the environment from
radiation exposure. The job of this section is to:
➢ Provide technical assistance to the organizations and communities that have to deal with
radiation problems or air pollution;
➢ Provide a monitoring program of the radiation’s fields in the environment;
➢ Deal with emergencies related to radiations;
➢ Evaluate the total risk associated with radiation exposure and air pollution.
This of course is true for each one of the 10 regions, into which the United States territory has
been divided. The chart in the next page shows in short EPA’s organization.

37
Office of The
Administrator
Region 1
Boston
Region 2
New York
Region 3
Philadelphi
a
Region 4
Atlanta
Region 5
Chicago
Region 6
Dallas
Region 7
Kansas
City
Region 8
Denver
Region 9
San Francisco
Region 10
Seattle
Office of Administration and
Resources Management
Office of Solid Waste and
Emergency Response
Office of Chemical Safety
and Pollution Prevention
Office of the Chief Financial
Officer
Office of Enforcement and
Compliance Assurance
Office of Environmental
Information
Office of General Counsel Office of Inspector General
Office of International and
Tribal Affairs
Office of Research and Development
Office of Air And
Radiation
Office of Air Quality Planning and
Standards
Office of Atmospheric
Programs
Office of Radiation and Indoor Air
Office of
Transportation and
Air Quality
Office of Water

38
13. How is Radon Concentration Calculated?
In the chapter regarding laws and regulations, we have seen all kind of limits (served as action
levels), concerning radon concentrations, that were established by different legislations. We
have also seen how the reference levels were different based on the house’s condition, whether
it was already built (and a mitigation process was needed) or under construction (in this case
radon resistant features could be used). However, we shall deepen into this argument later on.
We have also seen, although we have not yet focused on it, that these limits vary according to
individuals too. This can be easily understood if a separation is made between people. In
particular, we have individuals who work with sources of ionizing radiations and people who
do not. The limits concerning the former are higher than those related to the latter, which
means that the limits are more compelling for individuals who do not work with radiation’s
sources. Obviously this does not relate to any sort of radioresistance developed by the so called
‘radiation workers’. This is rather due to the fact that these individuals undergo medical
controls more often (nearly every 40 days).
Returning now to the indoor concentration issue, in this case the limit imposed may vary, as
already stated. This does not concern only houses, but also work places and schools. The
problem is that while the radon concentration in these places may be the same, the individuals
associated with them may vary. For example adults in work places and children in schools. In
this case the height of the individuals is not the only thing that has to be considered (radon,
being more heavy than air, tends to stratify at the bottom, making the children more exposed)
since the children’s radiosensitivity is higher. This can be seen considering the relation of the
effective dose:
𝐸 = ∑ 𝑤 𝑇 𝐻 𝑇
𝑇
= ∑ 𝑤 𝑇
𝑇
(∑ 𝑤 𝑅 𝐷 𝑇,𝑅
𝑅
)
Where ‘wT’and ‘wR’ are respectively the tissue and the radiation weighting factors. The former
takes into account the different radiosensitivity of the organs that were exposed, while the
latter is related to the type of radiation and on its energy. ‘HT’ is the equivalent dose (referred
to a particular organ), while ‘DT,R’ is the absorbed dose. Now, supposing that the absorbed
dose is the same for children and adults, the equation above shows that different tissue
weighting factors (higher in children) imply different values for the effective dose, that will
thus result higher in the children.
Furthermore, what varies the most among these places is the time that individuals pass in them.
For example, a period of time equal to 2000h per year is considered for work places, while
5000h yearly are considered for houses. In addition, this too leads to different exposure levels,
again, even if the radon concentrations are equal.
Before proceeding, we need to focus on the quantities used in the ‘radon field’, since they are
quite different from the one used, in general, in radiation protection.

39
It all starts with a problem, as most things; in particular, in this case the issue regards the
correlation between the concentration measured by the detector (alpha guards for example
measure the alpha particles emitted by 222
Rn) and the “real” effective dose associated with the
individual (we shall see later the reason of the quotation marks). This difficulty is related to a
chemical – nuclear characteristic of radon and his progeny.
Essentially, this situation takes place when two radionuclides (even though the case can be
extended to greater number of nuclei, as long as they are ‘related’, i.e. one decays into the
other and so on) that decay one into the other, are characterized by very different half-lives. In
particular, if the father’s half-life is longer than the one belonging to its daughter, after a certain
period of time, their activity equals. This phenomenon is called ‘secular equilibrium’.
The table showed to the left for
example, represents the case of 238
U
and 234
Th. Of course, the only activity
(and so the concentration) being
different from zero, at the beginning (t
= 0) is the one that belongs to the
uranium. Since no uranium atoms have
decayed yet, thorium is not present at
all. Over the time, uranium starts and
continues to decay and the thorium
concentration rises. Now, being
uranium the father, no decay
phenomenon can produce it, so by time its concentration starts to decrease. This of course
cannot be seen by the figure, since uranium’s half-life is extremely long (way more than the
time showed). This can apply also for a decay cascade, which means radon and its progeny are
included in it. So in theory, the activities of the radionuclides can be considered equal. In
reality this does not happen and we will explain why.
In the chapter concerning the geology of radon, we have seen how easily this element, being
a noble gas, can move through the soil and out of it. We have also seen that this does not apply
to his daughters, since they are reactive species. All these elements in fact (i.e. polonium, lead,
etc.) interact with the matter surrounding them, in particular with dust and walls, especially in
closed environments. The consequence is that while radon in a closed environment remains
effectively in the air, his progeny does not, and so their concentration in the atmosphere
decreases. Of course, the presence of dust enhances their concentration in the air, since it
prevents their attachment to walls and furniture.
This is why the measure given by the detector in terms of activity of radon is not representative
of the real one existing in that place, i.e. the activity of the daughters. This is quite important
since the daughters, as seen, are the ones that cause more damage to individuals. In addition,
this leads to the necessity of the identification of new quantities, which will be described in
the following part.

40
By now it should be clear that almost everything concerning radon “started with miners”, and
this is no exception. In particular, at the time, a sort of reference level for radon exposure in
mines was considered. This value was set equal to 100 pCi of radon concentration per liter of
air (i.e. 100 pCi/L). This value refers to the highest concentration of activity to which miners
could be exposed. Later on, understood that the real problem was related to its progeny, the
attention moved toward the daughters and, in particular, to the alpha particles emitted by these
radionuclides (we have also seen how the danger comes from these particles), therefore to their
energy.
It was then cleat that a new limit had to be settled, in order to take into account the energy that
the alpha particles (emitted by the radon progeny) could potentially release into the lungs.
Before getting to the actual quantities, let’s give some definitions that can be useful.
➢ The potential alpha energy of a single atom (εp), of the radon decay chain, represents
the total energy of the alpha particles released during the cascade decay, from the
considered radionuclides to the last one. In this case, the latter is 210
Pb, since its half-life
is much longer than the one of the previous daughters. In fact, this radionuclide is not
considered in the secular equilibrium;
➢ The potential alpha energy concentration (cp) which represents the sum of the energy of
all the alpha particles released by any mixture (still referred to radon progeny) of atoms
per unit of air:
𝑐 𝑝 = ∑ 𝑐𝑖(𝜀 𝑝,𝑖/𝜆 𝑟,𝑖 )
𝑖
Where 𝑐𝑖 is the activity concentration of the i-th radionuclide, while 𝜆 𝑟,𝑖 its decay constant.
The latter can be related with the half-life of the radionuclide with the following equation:
𝜆 𝑟 = ln(2) /𝑡1
2
,𝑟
The unit of measure of ‘cp’ in the International System is [J/m3
] (where 1 J/m3
= 6,242x1012
MeV/m3
). We may now introduce the ‘equilibrium equivalent concentration’, in short EEC.
This quantity refers to a mixture of radon progeny not in equilibrium with their father. It
represents the activity concentration of radon in equilibrium with its progeny that has the same
potential alpha energy concentration of the mixture that is not in equilibrium (i.e. the one
effectively present in the environment). We can thus write:
𝐸𝐸𝐶 = 0,105𝐶(𝑃𝑜218) + 0,516𝐶(𝑃𝑏214) + 0,379𝐶(𝐵𝑖214) + 6 ∗ 10−8
𝐶(𝑃𝑜214)
Whose unit of measure is [Bq/m3
]. The quantities designated with the letter ‘C’, represent the
different activity concentrations of the progeny, expressed in [Bq/m3
].

41
These are the effective activity concentrations found in the atmosphere (of the closed
environment); in short, the quantities that we wish to know. In particular:
➢ Activity concentration of 𝑃𝑜218
expressed in Bq/m3
;
➢ Activity concentration of 𝑃𝑏214
expressed in Bq/m3
;
➢ Activity concentration of 𝐵𝑖214
expressed in Bq/m3
;
➢ Activity concentration of 𝑃𝑜214
expressed in Bq/m3
.
The factors instead, represent the fraction of the potential alpha energy (with respect to the
total value) per unit of activity, of a particular radionuclide.
The values of the second column, except for the 218
Po, are equal due to the fact that, besides
214
Po, the remaining radionuclides are not alpha emitters (but beta particles emitters instead)
and thus are not taken into account.
Suppose now, we have a vial containing 100 Bq/m3
of 222
Rn in equilibrium with its progeny.
Imagine now that this vial does not let the daughters interact with its walls, we obtain a mixture
effectively in equilibrium, where the activity concentration is the same (as the father) for all
the daughters and equal to 100 Bq/m3
. Now, replacing the concentration ‘C’, in the EEC
equation, of each radionuclide with value of 100 Bq/m3
, what we find is of course an EEC that
equals exactly 100 Bq/m3
. This is quite obvious since we established that no radionuclide could
interact with anything in the vial.
The problem with the EEC equation is that the concentrations are not know, but a useful
equation comes in hand. The equation correlates the radon activity concentration of a non-in
equilibrium mixture (EEC), with the one measured in the particular closed environment. The
latter, as seen, is the one effectively present in the air, to which the activity concentration (of
the radon progeny) could not be related; due to the chemical reactivity of the radon decay
products. This relation is:
𝐹 =
𝐸𝐸𝐶
𝐶 𝑅𝑛
Radionuclide 𝑡1/2 𝜀 𝑝,𝑖 per atom
[Mev]
𝜀 𝑝,𝑖/𝜆 𝑟,𝑖 per unit
activity
[MeV/Bq]
𝑘 𝑝,𝑖
∗
=
𝜀 𝑝,𝑖/𝜆 𝑟,𝑖
∑ 𝜀 𝑝,𝑖/𝜆 𝑟,𝑖𝑖
𝑃𝑜218 3,05 min 13,69 3615 0,105
𝑃𝑏214 26,8 min 7,69 17840 0,516
𝐵𝑖214 19,9 min 7,69 13250 0,379
𝑃𝑜214 164 μs 7,69 2*10-3
6 ∗ 10−8

42
The left-hand member of the equation is called ‘equilibrium factor’, and its values do not
exceed unity. On the right-hand member of the equation we find the EEC, that has already
been described, and the ‘𝐶 𝑅𝑛’ which represents the measured radon concentration. This
equilibrium factor may be considered as the fraction of the measured radon concentration that
would be present in the air if the progeny mixture (the effective one) were in equilibrium with
the father radionuclide. It is a sort of correction factor, and it differs for outdoor environments
(for which F = 0,7) and for indoor environments (for which F = 0,5). These two values are
such that:
𝐸𝐸𝐶𝑖𝑛 < 𝐸𝐸𝐶 𝑜𝑢𝑡
Being easier for the progeny, to interact with matter, in a closed environment, the fraction of
the measured concentration will be higher in an open space.
Through this quantity, a measure of the total exposure could be obtained (or the one related to
a particular place). It is though necessary to know the time passed in that place, i.e. the
exposure time.
Assuming, for example, 5000h per year for homes, 2000h per year for a work place and 1700h
per year for an open space, the total exposure could be calculated this way:
𝐸(𝐵𝑞ℎ/𝑚3) = 5000 ∗ 𝐸𝐸𝐶ℎ𝑜𝑚𝑒 + 2000 ∗ 𝐸𝐸𝐶 𝑤𝑜𝑟𝑘 + 1700 ∗ 𝐸𝐸𝐶𝑒𝑥𝑡
If the results are needed in [Sv], a conversion factor could be used to convert the value in this
unit of measure:
3 ∗ 10−9
𝑆𝑣 𝑚3
𝐵𝑞 ℎ
Yet, another quantity has been introduced, that results useful when treating radon; it is the
‘Working Level’ (WL). In particular, 1WL = 1,3*105
Mev/L where the right-hand side of the
equation represents the total energy possessed by the alpha particles emitted by the decays of
the progeny in equilibrium with 100 pCi/L of radon. Since, as seen, 100 pCi/L represented the
reference level in mines, this has been chosen as key value to represent this quantity. Indeed:
1𝑊𝐿 = 1,3 ∗ 105
𝑀𝑒𝑉 𝑜𝑓 𝛼 𝑒𝑛𝑒𝑟𝑔𝑦 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑜𝑓 𝑎𝑖𝑟.
Now, this quantity needed a correlation with the exposure time; so this time the ‘Working
Level Month’ was established to represent the exposure at 1WL for a period of 170h (in order
to simplify the gathering of data). So that:
1𝑊𝐿𝑀 = 1𝑊𝐿 𝑒𝑥𝑝𝑜𝑠𝑢𝑟𝑒 𝑓𝑜𝑟 170ℎ.

43
Where 170h represented the number of hours in a month, for mineworkers. Since we are still
referring to exposure times, it is easy to see how that value needs changes in case it has to be
calculated for other places.
A number of conversion factors may result useful to correlate exposure and radon
concentration:
• 1𝑊𝐿𝑀 = 170ℎ ∗ 20.8
𝜇𝐽
𝑚3
= 3,54 𝑚𝐽 ℎ/𝑚3
;
• 1
𝑀𝐵𝑞 ℎ
𝑚3
= 2,22
𝑚𝐽 ℎ
𝑚3
;
• 1
𝑀𝐵𝑞 ℎ
𝑚3
= 0,628 𝑊𝐿𝑀.
Considering the first, it is helpful to remember that the WL may be expressed also in terms of
J/m3
:
1𝑊𝐿 = 1,3 ∗ 105
𝑀𝑒𝑉 = 2.08 ∗ 10−5
𝐽
𝑚3
It is thus possible to find the correlation between sievert and working level month, considering
a time exposure of 7000h/y for houses and 2000h/y for working places and using the
conversion factors seen above:
➢ In a house:
1
𝐵𝑞
𝑚3
= 0,0156
𝑚𝐽 ℎ
𝑚3
𝑐𝑜𝑛𝑠𝑖𝑑𝑒𝑟𝑖𝑛𝑔 7000ℎ 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟;
1
𝐵𝑞
𝑚3
= 0,0044 𝑊𝐿𝑀;
1𝑊𝐿𝑀 = 4𝑚𝑆𝑣
➢ In a working place:
1
𝐵𝑞
𝑚3
= 0,00445
𝑚𝐽 ℎ
𝑚3
𝑐𝑜𝑛𝑠𝑖𝑑𝑒𝑟𝑖𝑛𝑔 2000ℎ 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟;
1
𝑚𝐽 ℎ
𝑚3
= 1,4 𝑚𝑆𝑣;
1𝑊𝐿𝑀 = 5 𝑚𝑆𝑣.
Of course the two values differ from each other, being the time of exposure different (and so
does the number of hours to which the WLM is related).

44
A simple exercise could now be carried out, to see what difference, in terms of total exposure,
we have between an “average United States country” and Iowa. The quotation marks were
used to indicate that for the generic states, we shall use the yearly average values of
concentration of the Unites States. The calculation is made imagining that the concentration
levels found are the ones related to the EEC. Moreover, the right-hand side of the equation is
divided into two parts, where the first refers to indoor spaces as a whole (house and working
place for a total of 7000h per year) while the second to open spaces.
➢ Average state:
𝐸 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 = [7000ℎ ∗ 48,1
𝐵𝑞
𝑚3
∗ 3 ∗ 10−9
𝑆𝑣𝑚3
𝐵𝑞ℎ
] + [1700ℎ ∗ 14,8
𝐵𝑞
𝑚3
∗ 3 ∗ 10−9
𝑆𝑣𝑚3
𝐵𝑞ℎ
] =
= 1,01 𝑚𝑆𝑣 + 0,075 𝑚𝑆𝑣 = 1,08 𝑚𝑆𝑣
➢ Iowa:
𝐸𝐼𝑜𝑤𝑎 = [7000ℎ ∗ 315
𝐵𝑞
𝑚3
∗ 3 ∗ 10−9
𝑆𝑣𝑚3
𝐵𝑞ℎ
] + [1700ℎ ∗ 44,4
𝐵𝑞
𝑚3
∗ 3 ∗ 10−9
𝑆𝑣𝑚3
𝐵𝑞ℎ
] =
= 6,615 𝑚𝑆𝑣 + 0,226 𝑚𝑆𝑣 = 6,8 𝑚𝑆𝑣
The results show that the total exposure in Iowa is six times bigger than the one related to an
average state. In this case, the conversion factor (that permits us to obtain the results in terms
of Sievert) has been incorporated into the equation. The below table shows the mean
concentration values considered in the equation:
/ Iowa Average State
Indoor 8,5 pCi/L 1,3 pCi/L
Outdoor 1,2 pCi/L 0,4 pCi/L
Where the ‘pCi/L’ has been converted into ‘Bq/m3
, knowing that 1 pCi/L = 37 Bq/m3
.

45
14. Radon in Homes
We have discussed a lot about radon concentrations in houses or in general in closed
environments. We have seen how the action levels, recommended by particular agencies, vary
accordingly to the building considered. In particular, if the building is under construction or
has been already built. Considering the United States, let’s focus now on EPA’s
recommendations on the subject. Being the argument very large, it is useful to refer to the
scheme below; in fact, we shall proceed with this analysis following it.
The structure of the scheme and the arguments touched by it, are such that an individual of the
population might find his question and the relative answers in it; if, reading this work, he
arrives up to this point.
Radon Concentration in Homes
Living in the
Same Home
Buying or Selling a
New Home
Building a
New Home
Test for Radon
How?
Test Kits
Results
≥ 4 pCi/L< 4 pCi/L
Fix itSee if it
can get
any Lower
Check EPA zone
Test the House
Check EPA zone
EPA zone 1?
Use Radon
Resistant
Features

Radon in Iowa (U.S.A.)

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Radon in Iowa (U.S.A.)