8.15 Radiation Dosimetry
317
index is corrected for the effect of expected clouds, altitude, latitude, air pollutants,
surface albedo, and stratospheric ozone layer holes.
Because the radiation effects are dominated by single photon events, over a wide
range of intensities, the damaging effects of UV radiation will be proportional to the
UV index. For example, a value of 5 would produce the same sunburn in an hour as
a value of 10 in half an hour. Exposure of light skin to solar UV with index of 10
will produce a sunburn in about 12 min. If the UVI is 5, sunburn should be expected
after 24 min of exposure.
As UV is an ionizing radiation, damage to DNA can be expected. For UVB,
damage is mainly caused by the formation of a thymine-thymine cyclobutane dimer
mutation.
8.15.2 X-ray and Gamma Ray Damage
Although Wilhelm Röentgen and both Pierre and Marie Curie knew early in their
investigations that their newly discovered radiations from radioactive materials
could cause damage to the skin, the extent of the dangers from radiation-induced
cancer came some years later. In 1927, Hermann Muller showed that X-rays can
produce inheritable genetic damage. Even so, X-rays were being used often without
regard to safety precautions until the radiation effects of the atomic bomb in 1945
raised the public consciousness.
A single energetic ionizing particle can cause a double-strand break (DSB) of
a DNA molecule. 17 DNA damage may cause genetic instability or cell unviability.
Biological-cell systems have remedies, as indicated here:
8.15.3 Reactions by Cells to Radiation Damage
1. DNA repair mechanisms;
2. Radical scavenging;
3. Radiation-induced apoptosis;
4. Signals to neighboring cells to enhance their defenses;
5. Immune destruction of aberrant cells.
The remedies are known to be more effective at low dose levels. Counteracting
the defenses, cancers cells can mask their deviant behavior, and induce new blood
supply through their uncontrolled growth. These facts lead to the proposition that
humans will have imperceptible long-term damage by radiation if the dose is only
about 100 mGy.
The EAS is rather flat between 250 and 300 nm, but then drops rapidly for longer wavelengths,
being 0.1% at 330 nm as the EAS at 290 nm.
17 See Appendix E.
317
index is corrected for the effect of expected clouds, altitude, latitude, air pollutants,
surface albedo, and stratospheric ozone layer holes.
Because the radiation effects are dominated by single photon events, over a wide
range of intensities, the damaging effects of UV radiation will be proportional to the
UV index. For example, a value of 5 would produce the same sunburn in an hour as
a value of 10 in half an hour. Exposure of light skin to solar UV with index of 10
will produce a sunburn in about 12 min. If the UVI is 5, sunburn should be expected
after 24 min of exposure.
As UV is an ionizing radiation, damage to DNA can be expected. For UVB,
damage is mainly caused by the formation of a thymine-thymine cyclobutane dimer
mutation.
8.15.2 X-ray and Gamma Ray Damage
Although Wilhelm Röentgen and both Pierre and Marie Curie knew early in their
investigations that their newly discovered radiations from radioactive materials
could cause damage to the skin, the extent of the dangers from radiation-induced
cancer came some years later. In 1927, Hermann Muller showed that X-rays can
produce inheritable genetic damage. Even so, X-rays were being used often without
regard to safety precautions until the radiation effects of the atomic bomb in 1945
raised the public consciousness.
A single energetic ionizing particle can cause a double-strand break (DSB) of
a DNA molecule. 17 DNA damage may cause genetic instability or cell unviability.
Biological-cell systems have remedies, as indicated here:
8.15.3 Reactions by Cells to Radiation Damage
1. DNA repair mechanisms;
2. Radical scavenging;
3. Radiation-induced apoptosis;
4. Signals to neighboring cells to enhance their defenses;
5. Immune destruction of aberrant cells.
The remedies are known to be more effective at low dose levels. Counteracting
the defenses, cancers cells can mask their deviant behavior, and induce new blood
supply through their uncontrolled growth. These facts lead to the proposition that
humans will have imperceptible long-term damage by radiation if the dose is only
about 100 mGy.
The EAS is rather flat between 250 and 300 nm, but then drops rapidly for longer wavelengths,
being 0.1% at 330 nm as the EAS at 290 nm.
17 See Appendix E.