TCups said:
Could you provide some general comments on the quality of radiation radioactive contamination pertinent to the Fukushima events? I am not sure about the relationship of Sieverts and absorbed dosages of alpha, beta, gamma. Comparing exposure from nuclear accidents to absorbed dosage from diagnostic X-ray photons is apples to oranges, isn't it? Internal (ingested) exposure of radionuclides is a whole different set of risks and radiation injury than exposure to external x-ray and gamma radiation. It seems to me that most don't understand the difference and implications.
You question is very scientifically broad and difficult to put into layman's terms for the audience. However, Sieverts is absorbed dose in tissue (dose equivalent). See the difficulty, now I have to explain dose equivalent, which is a away of equating whole body exposure and internal exposure. Biological damage is primarily based on the rate and time of exposure (dose) and the organ of exposure. Dose rate alone cannot determine the true biological effects, and then not all doses produced the same effects per person. The same effects are generally noted only at extremely highl levels of dose equivalents (several Sieverts). However, the spent fuel process/weapons plant worker in Russia also should latent effects not expected for their ultra-high exposres to highly radioactive effluents from the plants. Dr. Marvin Goldman has written some papers on these cases.
For the most part, reporting agencies report dose equivalents for external gamma exposure to the whole body. All emergency action levels are based on external gamma radiation exposure and specific radionuclide concentrations in the air.
Unless you are within a highly contaminated zone with irradiated reactor wear products or areas coated with residual reactor coolant containing fission fragments, Alpha and beta exposure is less of a concern, and then only to the largest body organ (skin) and eyes. Any internal uptakes of such radioisotopes will be evaluated as Dose Equivalent then.
Sieverts are equivalent to REMs (Roentgen Equivalent Man) and Grays are equivalent to RADs (dose to materials). A quality factor is used to convert Grays to Sieverts.
The levels of radiation reported offisite are not significant in the big picture of personal radiation exposure or expected to produce any long range harmful effects to the public.
Those within the confines of the plant will be exposed to the radionuclides boiled off from the spent fuel pool, gamma shine from the spent fuel elements coming directly out of the pools (all combine pools), coolant waters with in pipes that also contain fission fragments from the degraded core, etc. Their dose equivalent (direct gamma exposure and uptake of various radionuclides (should be minimal due to the use respiratory equipment) are combine to control their exposures during emergency work.
When working in such an atmosphere of radionuclide gunk, the use of good respiratory equipment and protective clothing all controls to focus on whole body absorbed gamma dose to control overall dose to responders. It gets very sticky if uptakes and encountered and then directly dependent on the specific radionuclide.
Sorry about not getting into radiation biology, but it is very difficult subject and only worthy of non-hypothetical and very specific situations. Our cells are assaulted every minute of the day by high and low energy penetrating radiations, since time immortal. Some populated areas of the Earth have background radiation levels (airborne Radon and terrestrial gamma) 10 time higher averages than found in most US population centers.
Typical Radiation Protection Information:
http://www.nrc.gov/about-nrc/radiation/rad-health-effects.html"
More Detail Radiation Exposure infomation from HPS:
http://www.umich.edu/~radinfo/introduction/needtoknow/lstpart2-3.htm"
Dean Chaney, CHP
