Workshop Tutorials for Biological and Environmental Physics
QR15B: Radiation and the Body
A. Qualitative Questions:
1. We are exposed to radiation all the time, indoors and outdoors. This is called background radiation.
a. Give two examples of sources of this background radiation.
b. Which organ generally receives the most background radiation, and why?
There is some concern at the moment that pilots and flight attendants may have significantly higher
exposures to radiation than the normal exposure rates for the general public.
c. Why do pilots have a higher exposure to radiation than most other people?
2. A radiology nurse was found in the surgery late at night with her boyfriend in front of the x-ray
machine. She explained that she regularly gave him doses of x-rays as a contraceptive measure.
a. Discuss the value of x-rays as a contraceptive, and the possible side effects.
b. What is the difference between ionizing and non-ionizing radiation? Why does one cause genetic
effects but the other mainly somatic effects?
B. Activity Questions:
1. Measuring Radiation
Several different means of measuring radiation are shown.
Explain how they work.
Which ones would be suitable monitoring devices for persons working in a radiation area?
2. Exposure levels
Look at the chart showing the recommended exposure limits.
How do these compare with the dosages shown in the table?
What sort of professions do you think have the highest exposure?
3. Common sources of radiation
Use the counter to measure the radiation coming from the various sources.
How do they compare to background radiation?
How do they compare to the recommended maximum dosages?
The Workshop Tutorial Project –QR15B: Radiation and the Body
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C. Quantitative Questions:
Radiation (Counts per s)
1. Gold-198* is used to trace factory waste and sewage causing ocean pollution, and to trace sand
movement in river beds and on ocean floors. It decays as follows
79
Au  80Hg +- + .
You are measuring the attenuation of the radiation from a sample of 198Au through a new type of
shielding material which you intend to use when working at the sewage plant.
The proportion of  radiation penetrating a material decreases exponentially with the thickness of the
material. A shielding material is rated according to its attenuation coefficient,  = ln2/HVL. The HVL is
the half-value layer, which is the thickness which stops one half of the incident radiation. This thickness
depends on the material, and also on the radiation. It will be greater for more penetrating radiation.
a. Write an equation which gives the  radiation intensity at a distance d through some material.
b. Sketch the intensity of the  radiation as a function of distance.
c. Name another process which follows this form.
Use the graph to answer the following questions:
d. What is the half thickness of this
T h e a m o u n t o f r a d ia t io n v s s h ie ld in g
shielding?
t h ic k n e s s f o r G o ld - 1 9 8
e. What is the attenuation coefficient of the
lead shielding?
10
f. Using the graph, estimate the
radioactivity directly in front of the source
with no shielding.
g. You directly measure this activity with a
Geiger counter and find that it is much
higher than that predicted by the graph.
Why is this?
1
0
1
2
3
4
S h i e l d i n g T h ic k n e s s (m m )
2. Brent is changing the battery in the smoke detector when the phone rings. While he is answering the
phone Barry the dog chews up the detector and swallows the Americium source which it contains! Brent
is somewhat worried by this.
a. Complete the following reaction equation:
241
4
95 Am  ______ 2  .
It takes 9 hours for the source to pass through Barry, who weighs 25 kg. The half life for
241
95
Am is 433
years. The Am source in a standard smoke alarm has an activity of 1Ci (37 kBq), and each emitted 
particle has an energy of 5.4 MeV. The RBE factor for this radiation is around 15.
b. What is the resulting physical dose in Grays which Barry receives?
c. What is the dose equivalent in Sieverts?
d. Why are  sources only considered dangerous when inhaled or ingested?
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95
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The Workshop Tutorial Project –QR15B: Radiation and the Body