Radiation
• Objectives
– Understand the concepts of ½ life and ½ thickness in radiation
– Differentiate between fusion and fission
– Describe the processes involved in radioactive decays (alpha, beta, and gamma)
Elementary Particle Properties
Particle Symbol Charge
proton
p+
+1
electron
e-1
neutron
n0
0
Weight
Weight Ratio (e-)
1.007 amu 1838 heavy
0.0005 amu 1
light
1.008 amu 1840 heavy
1 Atomic Mass Unit (amu) = 1.66 x 10-24 grams
Atoms are electrically neutral with no net charge.
Ions are atoms that have been stripped of one
or more of their electrons and have a net charge.
Isotopes
• Identical Chemical Properties, Different Atomic Weight
• Difference = presence of number of neutrons in the nucleus
Hydrogen = 1.0079 amu
ISOTOPE Constituents
H
1 proton 1 electron
Deuterium 1 proton 1 electron
1 neutron
Tritium
1 proton 1 electron
2 neutrons
Atomic Mass Occurrence
1.0070 amu 99.985 %
2.0141 amu
0.014 %
3.0220 amu
0.001 %
Isotope Designations
Hydrogen
1
Helium-4
4
Uranium-235
235
neutron
proton
electron
1
1
H
1 proton, 0 neutrons
2
He
2 protons, 2 neutrons
92
n
1 p
1
0 e
-1
0
U
92 protons, 143 neutrons
Radiation
• Three types of Nuclear Radiation.
S
N
• Revealed by their deflection in a magnetic field as
neutral, charged negative or charged positive.
Radioactive Particles
• Alpha a
Ejection of 2 protons and 2 neutrons from an
4 He = a
unstable nucleus.
2
• Beta b
Ejection of an electron from an unstable nucleus
0 e = b
as part of the decay of a neutron.
-1
• Gamma g
Atomic nucleus transition, yielding high energy
photons.
Nuclear Reactions
226
88
Ra
222
86
Rn + 42He
Note that the numbers all add-up (conservation of particles).
A
ZX
A nucleons
Total particles in nucleus 226 = 222 + 4
Z protons
Number of protons
88 = 86 + 2
Alpha Decay
• Alpha a =
4
2He
Parent
226
Ra
Radium
Daughter
222
Rn
Radon
88
86
Radiation 42He
226
88Ra
a
222
56Rn +
4
2
He
Most of the energy is with the lighter particle, in this case
the alpha particle.
Beta Decay
• Beta b =
1
0
n
0
-1e
1
1
p + 0-1e
The decay of a neutron into a proton and electron.
Beta Decay
• Beta b =
1
0
n
0
-1e
1
1
p + 0-1e
The decay of a neutron into a proton and electron.
14
6C
90
38
Sr
14
90
0 e
N
+
7
-1
39
Y+b
(Radioactive Carbon)
Gamma Radiation
• Gamma g
E=hf
Very high energy photons are emitted from the nucleus.
Excess radiation emitted from an excited nucleus….
87
87
38Sr*
38
Sr + g
Excess radiation emitted as part of another process….
60
27Co
60
28
Ni + b + g
Radioactive Decay
If you start out
with a sample of
parent atoms (No),
after some time
there will be fewer
because of
radioactive decay
into the daughter
atoms.
Shielding
We can detect the radiation from a
radioactive source.
Say we get X counts/minute (cpm).
Geiger Counter
Shielding
We can shield the source with various
materials to test their usefulness in
protecting against the radiation.
Geiger Counter
Half Thickness
Half Thickness: The thickness of a material needed to
cut the count rate by 1/2.
If a 4 inch thickness of lead, drops a count rate
from 1000 cpm to 500 cpm, the half thickness must
be 4 inches.
Half Thickness
Half Thickness: The thickness of a material needed to
cut the count rate by 1/2.
If 12 inches of wood, drops a count rate
from 2000 cpm to 125 cpm, the half thickness must
be 3 inches.
2000
0
1000
3
500
6
250
9
125
12
Shielding Efficiency
a
b
g
Cotton Fabric
Wood
Lead
g’s are the most penetrating type of radiation.
Nuclear Energy Generation
Binding Energy/nucleon
Hydrogen
Uranium
Iron
Atomic Mass Number