2. CONTENTS
What is Radioactivity?
Radioactive Nuclei
 1) Strong Nuclear Force
 2) Stability of Nucleus
What are Radioisotopes?
 How many?
 How are they manufactured?
 Significance

3. What are Radioactive Decay?
 α Decay
 Decayβ
 Gamma Decay
The Decay Law, Decay Constant
and Half-life of radioactive Elements
What are the uses of Radioisotope?
What are the biological effect of
Ionization Radiation?

4.  Radioactive decay is the process in which an
unstable atomic nucleus loses energy by
emitting radiation in the form of particles or
electromagnetic waves.
 There are numerous types of radioactive decay.
The general idea:
An unstable nucleus releases energy to
become more stable

5. 1) Strong Nuclear Force
 The nuclear force (or nucleon-nucleon interaction or
residual strong force) is the force between two or
more nucleons. It is responsible for binding of
protons and neutrons into atomic nuclei. The energy
released causes the masses of nuclei to be less than
the total mass of the protons and neutrons which
form them.
 An important factor affecting nuclear force between
particles is a characteristic of each particles called
spin. When a neutron and a proton get together to
form a deuteron, it is only possible if the spin of the
two particles are parallel. When the spins are anti-
parallel, the nuclear force between them gets weaker
by the factor of 2.(stability of nucleus)
The nuclear strong force
and the
electromagnetic force are
the strongest of the
four fundamental forces

6. 2) Stability of Nucleus
 Each nucleus consists of a number of protons and neutrons. This items are
called nucleon. Whether the nucleus is stable or not, depends on the ratio
of the numbers of two particles. Nuclides with more neutrons or equal
numbers of neutrons and protons seem to be more stable. The separation
distance between nucleons is comparable to the range of the strong
nuclear force.
 The stable nuclides can be characterized as follows;
 The lightest nuclides have almost equal numbers of protons and neutrons.
 The heavier nuclides require more neutrons than protons.
 Most nuclides have both an even of number protons and an even number
of neutrons.
 The unstable nuclides, on the other hand can be characterized as follows;
 Disintegrations occur to produce daughter nuclei which are more stable
than the original or parent nuclei.
 The heavier nuclides decay such as to increase the number of protons. The
neutron to proton ratio decreases, thus shifting towards more stable nuclei.
 The nuclide residing below the stability line decay such as to decreases
the number of protons. The neutron to proton ratio increases, thus shifting
towards more stable nuclei.

7.  Atoms with a different number of neutrons than a usual atom,
with an unstable nucleus that decays, emitting alpha, beta and
gamma rays until the isotope reaches stability. Once it's
stable, the isotope becomes another element entirely.
Radioactive decay is spontaneous so it's often hard to know
when it will take place or what sort of rays it will emit during
decay.
How many?
 There are around 3800 radioactive isotopes. At
present there are up to 200 radioactive isotopes used
on a regular basis, and while some are found in
nature, most others have to be manufactured to suit
specific needs, such as for hospitals, research labs
and manufacturers.

8. How are they manufactured?
 Radioactive isotopes can be manufactured in
several ways, the most common by neutron
activation in a nuclear reactor which involves
capturing a neutron by the nucleus of an
atom which results in an excess of neutrons
(neutron rich). Some radioactive isotopes are
produced in a cyclotron in which protons are
introduced to a nucleus resulting in a
deficiency of neutrons (proton rich).

9. Significance
 Radioactive isotopes have very useful properties.
Alpha, beta and gamma radiation can permeate
solid objects like an x-ray, but are progressively
absorbed by them. The amount of this penetration
depends on several factors including the energy of
the radiation, mass of the particle, and density of
the solid. These properties can lead to many uses
for radioisotopes in the scientific, medical,
archaeological and industrial fields. The uses of
radioactive isotopes in these fields depend on what
element they become after they reach stability.

10.  Radioisotopes has unstable nuclei that does not have
enough binding energy to hold the nucleus together.
 Radioisotopes would like to be stable isotopes so
they are constantly changing to try and stabilize.
 In the process, they will release energy and matter
from their nucleus and often transform into a new
element. This process, called transmutation, is the
change of one element into another as a result of
changes within the nucleus.
 The radioactive decay and transmutation process will
continue until a new element is formed that has a
stable nucleus and is not radioactive. Transmutation
can occur naturally or by artificial means.

11.  The nucleus has too many protons which cause
excessive repulsion.
 In an attempt to reduce the repulsion, a Helium nucleus
is emitted. The way it works is that the Helium nuclei
are in constant collision with the walls of the nucleus
and because of its energy and mass, there exists a
nonzero probability of transmission. That is, an alpha
particle (Helium nucleus) will tunnel out of the
nucleus. Here is an example of alpha emission with
americium-241:
Alpha Decay of Americium-241 to Neptunium-237. Adapted
from Alpha Decay.

12.  Beta decay occurs when the neutron to proton
ratio is too great in the nucleus and causes
instability. In basic beta decay, a neutron is
turned into a proton and an electron. The
electron is then emitted. Here's a diagram of
beta decay with hydrogen-3:
Alpha Decay of Hydrogen-3 to Helium-3. Adapted from
Stability of Nuclei.

13.  There is also positron emission when the
neutron to proton ratio is too small. A proton
turns into a neutron and a positron and the
positron is emitted. A positron is basically a
positively charged electron. Here's a
diagram of positron emission with carbon-
11:
Positron Decay of Carbon-11 to Boron-11. Adapted from
Types of Radioactivity.

14.  The final type of beta decay is
known as electron capture and also
occurs when the neutron to proton
ratio in the nucleus is too small. The
nucleus captures an electron which
basically turns a proton into a
neutron. Here's a diagram of
electron capture with beryllium-7:
Electron Capture of Beryllium-7. It decays to Lithium-7.
Adapted from Electron Capture.

15.  Gamma decay occurs because the nucleus is at
too high an energy. The nucleus falls down to a
lower energy state and, in the process, emits a
high energy photon known as a gamma particle.
Here's a diagram of gamma decay with helium-3:
 Gamma Decay of Helium-3

16. The Decay Law, Decay Constant and Half
life of radioactive Elements
 Although the decay of radionuclides are
random and spontaneous, they occur according
to a certain law called the Decay law. The law
is described by parameters such as the decay
constant and the half-life of the particular
nuclide.

17. Radioactivity and the disintegration theory.
 The activity of a radioactive nucleus such as decays or
disintegration into other nucleus is a spontaneous and
random process. It means that, the process;
 Cannot be controlled
 Cannot be predicted
 Is independent and not effected by any chemical
combination or physical conditions like temperature or
presure.
 Radioactivity only involves the nucleus of the atom and not
any extra nuclear electrons (unlike chemical changes). It is a
way for unstable nuclei to attain stability.
 The disintegration process proceeds at a definite rate
through a certain number of stages until it reaches a stable
product.
 The process releases energies depending on the type of
particles emitted and the products of the disintegration.

18. Decay Law
 The laws for the radioactive decay physics given by the famous scientists Rutherford and
Fredrick Soddy. They both studied the radioactive decay experimentally. The laws for the
radioactive decay are as follows:
 Radioactive decay phenomenon is a spontaneous process. Radioactive decay process
does not depend on the external factors like temperature, pressure etc. It is impossible
to guess that which on the particular atom will decay in the particular interval of time.
 In the process of radioactive decay of an atom, either an alpha particle or a beta particle
is emitted. No any two particles emitted simultaneously . Even no two alpha or beta
particles simultaneously. At one time only one particle is emitted.
 The emission of an alpha particle from an atom causes the decrement of two in atomic
number and of four in mass number in the parent atom.
ZXA
Z–2 Y A– 4
+ 2 He 4
(alpha particle)
 The emission of a beta particle from an atom causes the increment in atomic number by one and
the mass number remains same.
ZXA
Z+1 Y A
+ -1e 0
(beta particle)
 The number of atoms decayed per second at any instant is directly proportional to the number
of atoms present in the sample at that instant. This law is also known as radioactive decay law.
 Thus, if in the sample the number of atoms is more, then the rate of decay is more and vice
versa.

19. Half-life of radioactive Elements
 There are a large range of half-lives seen in
nature
 Half-lives are unaffected by the nuclei’s
surroundings and only depend on what goes
on inside the nucleus
 238
U has a half-life of 4.5 billion years
 To summarize, one-half of the sample will
decay in one half-fife
 One-half of that one-half will decay in the
next half life
 One-half of that one-fourth will decay in the
next half life

21. What are the uses of Radioisotope?
 Very useful in many fields regardless of
whether there are found naturally or produced
artificially.
 Artificially produced radioisotopes are short life
(short half-life) but have greater activity
comparatively. It is easy to produced and one
can choose the suitable range and types of
energy required for specific purposes.
 Some of radioisotope uses employ the fact that
they are capable of producing radiation which
can be absorbed when they pass through matter.

22.  In nuclear medicine, radioisotopes are used as
tracer to identify location and concentration of
certain effected cells by measuring the radition
they emit.
Some of this uses are;
 Detecting underground pipe-line leakages such as
oil pipe-lines.
 Radioactive tracer in madicines, agriculture and
biological resear.
 In radiotherapty,gamma rays are used instead of the
expencive X-rays in the treatment of cancer.
 Gamma radiation used as sterilizing agents for
medical instumentation and bandages after
packaging.
 Dating archeological findings.

23. Radioisotope tracers
 The use of radioisotopes are tracers depends on the ability of the
radioisotopes to take part in the same prosess as its non-radioactive
isptopes.
 At the beginning, a selected radioisotope is injected into the patient’s
body. After some times duration, the patient will be subjected to the
body scan or any selected part of the body scans of the body.
 As examples, gamma ray scans the body such as the brain-scan can
map the concentration of the radioisotope in the patients.
 The information on the activity of different part of the brain can be
observed whereby tumor cells can be differentiated and identified.
 Radiotracer such Iodine-131 as be used as tracer for tyroid diseases.
 Radioisotope phosphorus used as agricultural traers as provided
information on the suitability of the types phosphate fertilizers for
particular crops and soil.

24. Carbon dating
 Carbon dating is a variety of radioactive dating which is
applicable only to matter which was once living and
presumed to be in equilibrium with the atmosphere,
taking in carbon dioxide from the air for photosynthesis.
 Cosmic ray protons blast nuclei in the upper
atmosphere, producing neutrons which in turn bombard
nitrogen, the major constituent of the atmosphere . This
neutron bombardment produces the radioactive isotope
carbon-14. The radioactive carbon-14 combines with
oxygen to form carbon dioxide and is incorporated into
the cycle of living things.
 The carbon-14 forms at a rate which appears to be
constant, so that by measuring the radioactive emissions
from once-living matter and comparing its activity with
the equilibrium level of living things, a measurement of
the time elapsed can be made.

25. What are the biological effect of
Ionization Radiation?
Characteristics
 One characteristic of ionizing radiation on human
body is that the energy absorbed is low but the
biological effects are serious. For example after
receiving a lethal dose of 10 Gy, the body
temperature will only increase by 0.02 o
C but the
dose may lead to death of all the exposed entities.
 The second characteristic is the latent biological
effects of radiation. Acute biological effects can
occur within several hours to several days while the
long term effects usually appear several years after
the exposure.

26. Type of effects
 Generally speaking, the biological
effects of ionizing radiation can be
classified according to the characteristics
of effects, occurring times and the object
that shows the effects.

27. Characteristic of effects Occurring time Object Effects on organs
Deterministic Effects
Acute Effects
Somatic Effects
Skin damage
Damage of reproductive system
Damage of blood forming system
Damage of digestive system
Damage of central nervous system
Latent Effects
Cataract
Damage of immunization system
Stochastic Effects
Cancer
Genetic Effects Heredity effects

28. The effects of critical organs
 Different organs have different sensitivity to
ionizing radiation. For example, gonad and bone
marrows are more sensitive organs, but the bones
are less sensitive.