322
8 Ionizing Radiation and Life
minimizing the damage, both short and long-term. For further investigations, see the
space physiology studies of Dr. Mary Anne Frey and her colleagues at NASA.
First colonization away from Earth will more likely be in near-Earth space
stations rather than Mars. The detailed engineering for such a venture was worked
out by Princeton Professor Gerald O’Neill and his students, in the late 1970s. 18
Using large rotating cylinders about 500 meters in diameter, radiation shielding
would come from the cylinder walls and the encapsuled air.
If you wish to drop your lifetime radiation exposure by a fourth, put meter-thick
purified lead walls, ceiling, floor and doors surrounding your bedroom. (Unpurified
lead is no good, as it has radioactive substances mixed in.) Of course, then you
would have to be careful to cover the lead, so you do not scrape or lick the walls.
But that’s not all. You would have to acquire special breathable air that has no radon
gas. This could be produced by containing a volume of air for many days to allow
radon decay, or by liquefying and then boiling above −183 ◦ C but below −61.7 ◦ C
to release nitrogen and oxygen, but leaving liquid radon.
Problems
8.1 We know that each human on Earth has about 10 14 neutrinos from the Sun
passing through their bodies every second. However, a solar neutrino will pass
through about 8×10 15 meters of tissue with only a 50-50 chance of hitting anything.
Estimate the number of neutrino hits in your body per day.
8.2 How much work must be done by an electric field to ionize nitrogen molecules
in air?
8.3 What is the lowest frequency of light that can break an organic chemical bond
formed by the release of 4 eV of energy?
8.4 If the physical half-life of iodine-131 is 8 days and the biological half-life of
iodine for a certain person is 70 days, calculate the percent of ingested iodine-131
left in the person after 10 days.
8.5 Suppose a 100 microcurie radioactive source of half-life 8 days and which
emits 0.2 MeV beta particles is placed within some tissue. How many disintegrations
occur each second in this source, initially? What is the activity of this source after
10 days?
8.6 A spectrophotometer passes light of wavelength 280 nm through a cuvette of
inside length 1.0 cm and holding a water solution with an unknown concentration
of a protein with an absorptivity of 59,000/M-cm. If the absorbance is measured to
be 0.0352, what was the molar concentration?
18 Gerald K. O’Neill, The High Frontier: Human Colonies in Space, [New York: William
Morrow & Company] (1977).
8 Ionizing Radiation and Life
minimizing the damage, both short and long-term. For further investigations, see the
space physiology studies of Dr. Mary Anne Frey and her colleagues at NASA.
First colonization away from Earth will more likely be in near-Earth space
stations rather than Mars. The detailed engineering for such a venture was worked
out by Princeton Professor Gerald O’Neill and his students, in the late 1970s. 18
Using large rotating cylinders about 500 meters in diameter, radiation shielding
would come from the cylinder walls and the encapsuled air.
If you wish to drop your lifetime radiation exposure by a fourth, put meter-thick
purified lead walls, ceiling, floor and doors surrounding your bedroom. (Unpurified
lead is no good, as it has radioactive substances mixed in.) Of course, then you
would have to be careful to cover the lead, so you do not scrape or lick the walls.
But that’s not all. You would have to acquire special breathable air that has no radon
gas. This could be produced by containing a volume of air for many days to allow
radon decay, or by liquefying and then boiling above −183 ◦ C but below −61.7 ◦ C
to release nitrogen and oxygen, but leaving liquid radon.
Problems
8.1 We know that each human on Earth has about 10 14 neutrinos from the Sun
passing through their bodies every second. However, a solar neutrino will pass
through about 8×10 15 meters of tissue with only a 50-50 chance of hitting anything.
Estimate the number of neutrino hits in your body per day.
8.2 How much work must be done by an electric field to ionize nitrogen molecules
in air?
8.3 What is the lowest frequency of light that can break an organic chemical bond
formed by the release of 4 eV of energy?
8.4 If the physical half-life of iodine-131 is 8 days and the biological half-life of
iodine for a certain person is 70 days, calculate the percent of ingested iodine-131
left in the person after 10 days.
8.5 Suppose a 100 microcurie radioactive source of half-life 8 days and which
emits 0.2 MeV beta particles is placed within some tissue. How many disintegrations
occur each second in this source, initially? What is the activity of this source after
10 days?
8.6 A spectrophotometer passes light of wavelength 280 nm through a cuvette of
inside length 1.0 cm and holding a water solution with an unknown concentration
of a protein with an absorptivity of 59,000/M-cm. If the absorbance is measured to
be 0.0352, what was the molar concentration?
18 Gerald K. O’Neill, The High Frontier: Human Colonies in Space, [New York: William
Morrow & Company] (1977).