1. Biological Effects of Radiation.
Because the many of the problems associated
with nuclear power plants are associated with
the biological effects of nuclear radiation,
we will reverse the order and discuss biological
effects first.
It is known that the biological effects of exposure
to radioactive materials can be serious, but in
many cases the mechanisms of damage are
not understood at the atomic level so we need
to use information from biological experiments.

2. Units. Unfortunately many units are used to
Describe radiation exposure:
Energy exposure:
1 rad = 10-5 joules in 1 gram of tissue
Quality factor: Takes account of the fact that
Different kinds of radiation have different
Biological effects
1 rem = (Quality factor)x 1 rad

3. Table 15-1, p. 505

4. Table 15-2, p. 506

5. Lethal Dose 50%
Animals (including humans) exposed to
intense radiation become ill and die of various
diseases, mainly cancers. The deaths may
occur quickly or over many decades and the
responses are not the same for all individuals.
The mechanisms of damage are not well understood
and the available information is from data
from experiments. The data can be arranged in
a dose-response curve as shown on the next
slide
Note that what matters biologically is the total
dose to the organism and not the rate of exposure.

6. The dose at which 50% die is called the lethal-dose 50
Figure 15.2: Dose-effect distribution curve for mice. The point at which 50% of the population dies is called the lethal dose-50, or LD-50. It is about 1000 rads in this example.
Fig. 15-2, p. 507

7. Unfortunately we do have such data for
humans as a result of the bombs dropped on
Hiroshima and Nagasaki in 1945.
By following the histories of 24,000 people
exposed to intense radiation in those events,
data including that displayed in the following
graph was obtained.

8. Figure 15.3: Leukemia mortality dose-response curves for Hiroshima and Nagasaki.
Fig. 15-3, p. 508

9. Note that the numbers are per million person
years.
This data implies roughly
2 cases per rem of radiation
per million people per year for leukemia.
There is debate concerning whether such high
dose data can be extrapolated to determine
risks at low doses, but most scientists believe
that it can.

10. If there are 1200 leukemia deaths
per million person years at a dose
of 250 rads, what are your chances
of getting leukemia from the
background radiation of 360 millirads
per year in a lifetime of 70 years?
(assuming quality factor =1)
A. 1 in 1200x106
B. 1 in 1200x(.360/(250x70))x106
C. 1 in 250 x 106/(1200x70x0.360)
D. 1 in (1200x70 x.360)/(250 x 106)
E. 1 in 1200x250x106/(70 x.360)

11. Answer C:
Number of deaths per person year per
Rad = 1200/(106 x250)
Exposure of one person in 70 years
= 1x70x.360 rads
Number of deaths expected is the product
= /(250x106) deaths per person per rad per year
x 1 person x 70 years x .360 rads
Or one death for every
((250x106)/(1200x70 x.360) about 8200 people

12. Actual leukemia death rates are around
1 for every 10,000 people per lifetime.
So the exercise gave an answer close
to what is observed.
However that is somewhat surprising.
The curve is S-shaped, so the death rate
would be expected to be much lower at low doses.
This suggests that other origins of
leukemia may be important.

13. Background radiation:
In evaluating the risk of nuclear power plants
it is necessary to take into account that humans
are exposed to significant nuclear radiation
in the absence of power plants or nuclear weapons.
A summary appears on the next slide.

14. Table 15-5, p. 514

15. These radiation exposures do have health
effects. Unless nuclear power
significantly increases this exposure it would
be rational to worry first about the other
exposures. These include particularly radon.
Measures you can take to protect yourself against
excessive radon exposure are discussed in
your book.
Current national standards limit radiation exposure
above background to 100mrem/yr

16. Table 15-3, p. 508

17. From these tables, what kinds of health effects can
be expected from the average background exposure
during a 70 year human life? (Assume QF=1.)
A. None
B. blood changes.
C. injury and disability
D. between B. and C.
E. between A. and B.
Table 15-3, p. 508

18. Answer: D. between B and C
360 mrem/yr x(1/1000 rem/mrem) x (1/QF (rad/rem))
X70 yr =
25.2 rad
Some effects!

19. Decay of Radon, naturally occurring in common rocks
Figure 15.4: Dose-response curves for low doses of radiation are based on the assumption of a linear response—that is, that the data from high doses (solid curve) can be extrapolated back to low doses (as in curve a). No threshold exists (as is assumed for curve b), so that any radiation is assumed to have a harmful effect.
Fig. 15-5, p. 510

20. Medical Procedure exposures
Table 15-4, p. 514

21. Figure 15.7: Key to major radon entry routes.
Fig. 15-7, p. 512

22. Figure 15.6: Comparable risks from exposure to radon gas.
Fig. 15-6, p. 511

23. Somatic and genetic damage:
The biological effects discussed so far are
to the individual irradiated (somatic)
There are also effects on the descendants
of the irradiated individuals through damage to
the DNA molecules which carry genetic information.
Such mutations are known to be a major source of
the variation which, together with natural selection,
drives biological evolution. They occur naturally,
driven by the background radiation.
However most mutations fail (do not produce
improvements in survivability) and too many
mutations will threaten the survivability of a
species.

24. Exposures from various other hazards above
‘background’
Proposed standard for the Yucca Mountain
high level waste storage site: 15mrem/yr for
10,000 years (may not be achievable)
Normal nuclear reactor operation for electric
power production: 170 mrem/yr (federal limit)
Chernobyl (worst nuclear power accident
until Fukushima)
200 mSv= .2 x100 rem/SV x 1000mrem/rem
= 20,000mrem
Nuclear bomb: Exposures and Hiroshima
and Nagasaki were (for survivors)
from rads=
100, ,000 mrem ( if QF=1 bone marrow only)

25. Summary and conclusions:
Radiation from radioactive (decaying) nuclei
has mainly deleterious effects on biological
organisms including humans.
Humans are all exposed to substantial, naturally
occuring radiation, most significantly from radon.
Much the biggest biological threat to human health
from nuclear radiation arising from human activity
is from nuclear weapons, if they are ever used again.
The other dangers are from nuclear power plant
accidents and extremely long term storage of
nuclear waste. The federal limit on exposure
from normally operating nuclear power plants
Is about 20% above normal background.