1. Radioactivity

2. Radiation
Radiation: The process of emitting
energy in the form of waves or
particles.
Where does radiation come from?
Radiation is generally produced
when particles interact or decay.
A large contribution of the radiation
on earth is from the sun (solar) or
from radioactive isotopes of the
elements (terrestrial).
Radiation is going through you at
this very moment!
http://www.atral.com/U238.html

3. A. Definitions
• Radioactivity
– emission of high-energy radiation from the
nucleus of an atom
• Nuclide
– nucleus of an isotope
• Transmutation
– process of changing one element into another
via nuclear decay

4. Isotopes
What’s an isotope?
Two or more varieties of an element
having the same number of protons but
different number of neutrons. Certain
isotopes are “unstable” and decay to
lighter isotopes or elements.
Deuterium and tritium are isotopes of
hydrogen. In addition to the 1 proton,
they have 1 and 2 additional neutrons in
the nucleus respectively*.
Another prime example is Uranium
238, or just 238U.

5. Radioactivity
By the end of the 1800s, it was known that certain
isotopes emit penetrating rays. Three types of radiation
were known:
• Alpha particles (α)
• Beta particles (β)
• Gamma-rays (γ)

6. B. Types of Radiation
• Alpha (α)
4
– helium nucleus
2 He 2+ paper
 Beta-minus (β-)
0 1-
-1 e
lead
 electron
 Gamma (γ)
 high-energy photon 0 concrete

7. C. Nuclear Decay
• Why nuclides decay…
– to obtain a stable ratio of
neutrons to protons
39
19 K Stable
40 Unstable
19 K (radioactive)

8. C. Nuclear Decay
TRANSMUTATION
• Alpha Emission
238
92 U→ Th + He
234
90
4
2
 Beta Emission
131
53 I→ 131
54 Xe + e
0
-1

9. Where do these particles come
from ?
These particles generally come
from the nuclei of atomic isotopes
which are not stable.
 The decay chain of Uranium
produces all three of these forms
of radiation.
 Let’s look at them in more detail…

10. Note: This is the
atomic weight, which
is the number of
Alpha Particles (α)
protons plus neutrons
Radium Radon
+ n p
p n
R226 Rn222
α (4He)
88 protons 86 protons 2 protons
138 neutrons 136 neutrons 2 neutrons
The alpha-particle (α) is a Helium nucleus.
It’s the same as the element Helium, with the
electrons stripped off !

11. Beta Particles (β)
Carbon Nitrogen + e-
C14 N14
6 protons 7 protons electron
8 neutrons 7 neutrons (beta-particle)
We see that one of the neutrons from the C14 nucleus
“converted” into a proton, and an electron was ejected.
The remaining nucleus contains 7p and 7n, which is a nitrogen
nucleus. In symbolic notation, the following process occurred:
Yes, the same
np+e (+ν)
neutrino we saw
previously

12. Gamma particles (γ)
In much the same way that electrons in atoms can be in an
excited state, so can a nucleus.
Neon Neon
Ne20 Ne20 +
10 protons 10 protons gamma
10 neutrons 10 neutrons
(in excited state) (lowest energy state)
A gamma is a high energy light particle.
It is NOT visible by your naked eye because it is not in
the visible part of the EM spectrum.

13. Gamma Rays
Neon
Ne20
Neon
Ne20 +
The gamma from nuclear decay
is in the X-ray/ Gamma ray
part of the EM spectrum
(very energetic!)

14. How do these particles differ ?
Change in Change in
Particle Mass atomic
number number
Gamma (γ) No change No change
Increased by
Beta (β) No change
1
Decreased Decreased
Alpha (α)
by 4 by 2

15. Rate of Decay
Beyond knowing the types of particles which are emitted
when an isotope decays, we also are interested in how frequently
one of the atoms emits this radiation.
 A very important point here is that we cannot predict when a
particular entity will decay.
 We do know though, that if we had a large sample of a radioactive
substance, some number will decay after a given amount of time.
 Some radioactive substances have a very high “rate of decay”,
while others have a very low decay rate.
 To differentiate different radioactive substances, we look to
quantify this idea of “decay rate”

16. Half-Life
 The “half-life” (h) is the time it takes for half the atoms of a
radioactive substance to decay.
 For example, suppose we had 20,000 atoms of a radioactive
substance. If the half-life is 1 hour, how many atoms of that
substance would be left after:
#atoms % of atoms
Time
remaining remaining
1 hour (one lifetime) ? 10,000 (50%)
2 hours (two lifetimes) ? 5,000 (25%)
3 hours (three lifetimes) ? 2,500 (12.5%)

17. D. Half-life
• Half-life (t½)
– time it takes for half of the nuclides in a
sample to decay
Nuclear Decay
20
Example Half-lives 18
16
polonium-194 0.7 seconds
Mass of Isotopes (g)
14
12
lead-212 10.6 hours 10
8
iodine-131 8.04 days 6
4
carbon-14 5,370 years
2
0
0 2 4 6 8 10
uranium-238 4.5 billion years # of Half-Lives

18. Half-life
 How much of a 20-g sample of sodium-24 would
remain after decaying for 30 hours? Sodium-24 has
a half-life of 15 hours.
GIVEN: WORK:
total time = 30 number of half-lives = 2
hours 20 g ÷ 2 = 10 g (1 half-
t1/2 = 15 hours life)
original mass = 10 g ÷ 2 = 5 g (2 half-
20 g lives)

19. Writing Nuclear
Equations

20. Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number A
ZX
Element Symbol
Atomic Number
proton electron α particle
1
1
p or 1H
1 0
-1 e or -1β
0 4
2 He or 2α
4
A 1 0 4
Z 1 -1 2

21. Po decays by alpha emission. Write the balanced nuclear
212
equation for the decay of 212Po.
alpha particle - 4
2 He or 2α
4
84Po 2 He + ZX
212 4 A
212 = 4 + A A = 208
84 = 2 + Z Z = 82
84
212
Po 2
4
He + 208Pb
82
23.1

22. Write Nuclear Equations!
Write the nuclear equation for the beta
emitter Co-60.
60 0 60
Co e + Ni
27 -1 28

23. Write Nuclear Equations!
Write an equation to describe the beta decay of a lead-214
nucleus to form a bismuth-214 nucleus.
214
Pb 0
e + 214
Bi
82 -1 83
Write an equation to describe the alpha decay of a
radium-226 nucleus to form a radon nucleus.

24. Summary
 Certain particles are radioactive and undergo decay.
 Radiation in nuclear decay consists of α, β, and γ particles
 The rate of decay is give by the radioactive decay law:
 After 5 lifetimes more than 99% of the initial particles
have decayed away.

 Subatomic particles usually have lifetimes which are
fractions of a second…

25. A. F ission
• splitting a nucleus into two
or more smaller nuclei
• some mass is converted to
large amounts of energy
1
0 n+ 235
92 U→ 141
56 Ba + Kr + 3 n
92
36
1
0

26. A. F ission
• chain reaction - self-feeding reaction

27. B. Fusion
• combining of two nuclei to form one
nucleus of larger mass
• produces even more
energy than fission
• occurs naturally in
stars

28. A. Nuclear Power
• Fission Reactors Cooling
Tower

29. A. Nuclear Power
• Fission Reactors

30. A. Nuclear Power
• Fusion Reactors (not yet sustainable)

31. A. Nuclear Power
• Fusion Reactors (not yet sustainable)
National Spherical
Torus Experiment
Tokamak Fusion Test Reactor
Princeton University

32. A. Nuclear Power
F F
I U
s S
s I
vs.
i O
o N
n
• 235U is limited • Hydrogen is abundant
• danger of meltdown • no danger of
meltdown
• toxic waste
• no toxic waste
• thermal pollution
• not yet sustainable

33. • Choose one of the following to investigate:
– Irradiated Food
– Radioactive Dating
– Nuclear Medicine
– Weapons of mass destruction
– Chernobyl
– Nuclear power future
– Meltdowns/ leaks
• Make a mini-poster to display what you have