Radiation and Radioactivity
David Hahn “The Radioactive Boyscout” 1976-
Known for attempting to
make a fast-breeder
reactor in his backyard at
age 17
How might you distinguish Alpha, Beta and Gamma
radiation experimentally?
How might you distinguish Alpha, Beta and Gamma radiation
experimentally?
Magnetic Field
β-decay
Weak interaction can transform a proton into a neutron or a neutron into a proton
(It’s actually happening at the quark level)
β- decay:
n  p + ee-: electron
β+ decay: p  n + e+
e+: positron
Electronic Conversion: p + e-  n
β- decay
Proton
e-
udu
W-
Neutron
udd
νe
α-decay
U
α-particle = 4He:
cluster in the nucleus – α: very tightly bound system
2
Tunnel effect (decay probability)
r
A
Z
X N
A-4
Z-2
4
2
Y N-2 + He 2 + Q
Q-value energy (Q>0, because the decay occurs spontaneously)
 Q = [mX-mY-mHe].c2
Radiation and Doses
• A number of units are used to describe radiation and its
effects on biological material
Common Unit
SI Unit
Description
Application
1 Curie (C)
3.7x1010 decays
1Becquerel (Bq)
1 decay
Activity
Describe amount of
material
ie 1 μC of 137Cs
Rad
0.01 Joule/Kg
Gray (G)
1Joule/Kg
Absorbed Dose
How much Energy
is absorbed
Equivalent Dose
Absorbed x Relative
Biological
Effectiveness (RBE)
Biological Damage
RBE
10-20
Alpha
1-2
Beta
1
Gamma
REM
Rad x RBE
Example of a Decay Chain (238U)
INCREASING DOSE
Scale of Effects of Radiation Exposure
Over 5000 rem
Death within 1-2 days
1000 – 5000 rem
Death within 1-2 weeks
1000 rem
80-90% death rate
500 rem
50% death rate
100 rem
Detectable damage to bone marrow
5 rem
Annual Occupational Dose Limit
0.2-0.5 rem
Typical annual dose (background, lifestyle)
.01 rem
Chest X-ray
The Radium Girls
The Radium Girls
In the early 1920s, about 70 women were hired at the radium factory in New Jersey where they worked as dial painters
and used luminescent paint. They assumed they were not using anything poisonous. Even though some women thought it
was strange that when a few of them blew their nose the handkerchief glowed in the dark, they thought the stuff was
harmless. Some women even painted their nails and their teeth to surprise their boyfriends when the lights went out. At
work, the women were painting glow-in-the-dark radium compounds on the dials of watches and clocks. The women sat
at long tables row after row. Dials waiting to be painted sat nearby. Each day they would mix up glue, water and radium
powder (a mixture of radium salts and zinc sulfide, ZnS) into a glowing greenish-white paint. With care they would then
apply it with camel hair brush to dial numbers. As the brush lost its shape, the paint couldn't be applied accurately, so the
women would put the brush in their mouth and use the lips to make a point. The paint has no taste, and the women
didn't know it was harmful. In those days most people thought radium was a scientific miracle for curing cancer and other
medical problems. Unfortunately, for many of these women it did just the opposite. After several years of working as a
dial painter, some women's teeth started falling out and their jaws developed a painful abscess.
(…)
The glow effect that was seen with the dial painters was the result of ionization of atmospheric gases, producing a blue
glow. The blue glow can be enhanced in luminescent paints by the addition of zinc sulfide (ZnS). As the alpha particles
strike the ZnS, visible light is emitted in response to the ionizing radiation.
By the end of the 1920s, many of the dial painters died from symptoms associated with radium poisoning.
From: www.unco.edu/chemist/Bulletin/Chem101/radium.htm
Question:
Why is ingesting Radium (Ra) so harmful?
Why is ingesting Radium (Ra) so
harmful?
Radium is especially dangerous
because the configuration of its
outer electrons are similar to that
of Calcium. So it can form
chemical bonds in the same way
that Calcium does.
Calcium is one of the elements in
bone.
Ingested Radium can replace
Calcium in bone to become a
long lasting internal radiation
source. Leukemia and other
cancers can result.
222Ra
t1/2 = 1601 years
From E-Bay Nov. 29th 2010
“FITRITE RADIUM OUTFIT NOTE!!!!!NOTE!!!!!
This is a radium outfit used to put luminous material on watch
hands and/or dials. The box says it is easily applied and dries
quickly. The directions are on the box, which is original. There are
2 cans of material, one light and one dark and they have been
used. There is a metal tool for application.” (Description posted)
How to describe radioactive decays ?
Radioactive decay represents changes of an individual nucleus.
HOWEVER: quantum mechanics prevents us
from describing the decay of a single nucleus !!!
Houston, we have a problem.
Because, usually one looks at the decay of a large number of nuclei (N>>1), one can
describe radioactive decay statistically.
Decay is proceeding at a certain rate  Activity (A) [decays/s]
Units:
1 Becquerel = 1 Bq = 1 decay per second
1 Curie = 1 Ci = 3.7 x 1010 decays per second (old unit still widely used)
(activity of 1g of radium)
Formalism (I)
The activity of a certain sample (e.g. source) depends on the number N of
radioactive nuclei and on the probability λ for each nucleus to decay:
A=λ.N
[1/s]
Evolution with time:
[1/s]
dN = -A.dt
dN: number of nuclei that decayed during dt
 dN = -λ.N.dt, which gives:
Solving the differential equation:
dN/dt = -λ.N
 Radioactive decay law
N(t) = N0.e-λ.t
N(t=0)
Formalism (II)
Similarly, we find that the activity of a source change with time:
A(t) = A0.e-λ.t
From λ = decay constant, one can define τ = 1/λ, the mean lifetime
It is usual to define t1/2, the half-life, the time after which half of the initial
nuclei have decayed:
t1/2 = ln 2 / λ = τ ln 2
The half-life is characteristic to the decay of
a given nucleus. This number (when known)
is usually tabulated.
Conservation laws
• Conservation of Energy
• Conservation of linear momentum
• Conservation of angular momentum
• Conservation of electric charge
• Conservation of mass number A
 e.g. total number of nucleons is conserved, but Z and N can change