Radiation

Health Effects of Radiation Measures 1. radioactive half life: time for material to lose half of its radioactivity 2. biological half life: time for living tissue to eliminate, through biological processes, half of a given amount of substance 3. effective half life: (biological half-life * radioactive half-life) / (biological half-life + radioactive half-life) For example, if the radiaoactive half life of a material is 6 days and the biological half life is 3 days, then: effective half life = (6*3) / (6+3) = 18/9 = 2 days Acute effects 4. CNS syndrome: • • 100,000 RADs: death in seconds 10,000 RADs: death in minutes to hours 5. GI syndrome: • 1,000 RADs: death in 30-60 days 6. Bone marrow syndrome: • • • 300-500 RADs: median lethal dose (also called the LD50, which means lethal dose to half the exposed population) 150-200 RADs: anemia is significant, but recovery can occur 75-125 RADs: nausea, fatigue (often associated with medical treatments of radiation) 7. Other: • • 25-75 RADs: blood cell damage < 25 RADs: no detectable effects in the short term Chronic effects 8. somatic: skin conditions, alopecia (hair loss), infection, cataracts, cancer 9. genetic (DNA): mutations, birth defects Radiation Controls A. Agencies 1. Nuclear Regulatory Commission: "inside the fence" (of nuclear facilities) The NRC has principle jurisdiction for regulating nuclear facilities (i.e., "inside the fence"). 2. Environmental Protection Agency: "outside the fence" (of nuclear facilities) The EPA has principle jurisdictin for setting standards in the community (i.e., "outside the fence" of nuclear facilities) 3. Dept. of Energy: research and development The DOE is also the principle jurisdiction for investigating accidents at nuclear facilities. 4. Others: • • • • • • • Public Health Service (standards for medical treatment) Dept. of Transportation (transporting nuclear materials) Dept. of Interior (mining of nuclear materials) NIOSH, OSHA (occupational standards for radiation) FDA (medical devices) NCRP -- National Council on Radiation Protection ICRP -- International Council on Radiation Protection 5. California: California Radiation Control Law (CA Health and Safety Code) B. Standards 6. 500 mREMs / year: general population 7. 5,000 mREMs / year: occupational population The reason that occupational populations are allowed more exposure in a year is because they tend to be a healthier population, they tend to have closer monitoring of exposures, and it is generally easier to remove them from a radiation source should the exposures increase. 8. 25 mREMs / year: outside nuclear facilities Notice that the standards for exposures outside a nuclear facility is very strict in comparison to the general standards listed above. Part of this is due to the fact that it is only one source of radiation exposure, and part of it is undoubtedy due to the public concerns of nuclear facilities. 9. ALARA: as low as reasonably achievable A principle that can be found thought radiation controls is that exposures should always be as low as is reasonably achievable, even if it is much lower than the above standards. This principle is related to the Best available Technology that we have mentioned in air quality standards. C. Technological Controls 10. distance: (between source and person) inverse square law The inverse square law says that the exposure from a radiation source is inversely proportional to the square of the distance. This means that if we double the distance (2), the exposure is cut to one fourth of the original exposure ( 1 / 22 ). If we tripled the distance (3), the exposure is cut to one ninth of the original exposure ( 1 / 32 ). This tells us that there is a tremendous benefit in putting distance between you and the source of radiatio exposure. 11. time: (minimize); spacing allows for recovery It may seem obvious that the less time we are exposed to radiation, the better off we are. But the benefits are magnified by the fact that spacing of exposures allows the body to recover. For example, if a single exposure of 100 milli-REMs is compared to 10 exposures of 10 milli-REMs, the effect is much less if the dose is spread out over the 10 exposures. 12. monitoring: film badges, finger rings, etc. 13. shielding: barrier between source and person (half value layer: thickness needed to cut radiation in 1/2) 14. contamination prevention: filters, hoods, protective clothing, respirators 15. equipment testing: X-ray equipment, etc. RADIATION APPLICATIONS Objective: To provide a few examples of the positive applications of our knowledge of radiation. 1. Iodine-131 tracers: "radioactive cocktail" A. beta radiation 1/2-life = about 8 days B. used to study thyroid activity and thyroid treatment (thyroid concentrates iodine) note: 99.9% eliminated in about 80 days 2. NAA (neutron activation analysis): "atomic fingerprint" A. bombard sample material with neutrons B. measure frequency and intensity of resultant gamma radiation C. used to measure trace quantities of pollutants (e.g., heavy metals) 3. Americium-241 A. alpha radiation 1/2-life = about 400 years B. on end of lightning rods, increases attraction C. also used in smoke detectors: ionizes air between two electrodes (creates current) smoke interferes with current, thereby activating alarm risk of cancer is negligible and outweighed by risk of fires 4. Cobalt-60 A. cheapest form of gamma radiation B. used in cancer treatments, food irradiation 5. Carbon dating (Carbon-14) A. how carbon-14 is created in air: cosmic rays include neutrons: N + N ---> C + H in air, C-14 is at stable concentration in CO2 exception -- 20th century activities: atomic bomb testing increased CO2 levels B. how Carbon-14 is used to date materials (e.g., paper) plants take in CO2 (photosynthesis) when plants are alive, in equilibrium with environment upon plant death, C-14 undergoes beta decay (e.g., paper) 1/2-life = 5,760 years carbon dating accurate up to 50,000 years