Radiological effect

The neutrons in a research reactor can be used for many types of scientific studies, including basic physics, radiological effects, fundamental biology, analysis of trace elements, material damage, and treatment of disease. Neutrons can also be dedicated to the production of nuclear weapons materials such as plutonium-239 from uranium-238 and tritium, H, from lithium-6. Alternatively, neutrons can be used to produce radioisotopes for medical diagnosis and treatment, for gamma irradiation sources, or for heat energy sources in space. 

Cross-comparing the risks of various activities is difficult because of the lack of a common basis of comparison, however Cohen and Lee, 1979 provide such a comparison on the basis of loss of life expectancy. Solomon and Abraham, 1979 used an index of harm in a study of 6 occupational harms - three radiological and three nonradiological to bracket high and low estimates of radiological effects. The index of harm consists of a weighting factor for parametric study the lost time in an industry and the worker population at risk. The conclusions were that the data are too imprecise for firm conclusions but it is possible for a radiation worker under pessimistic health effects assumptions to have as high index of harm as the other industries compared. 

Eleven months after intratracheal and intraperitoneal injection of thorium dioxide in rats, a sharp and persistent fall in blood pressure was found (Syao-Shan 1970). The fall in blood pressure could not be directly attributed to the chemical or radiological effects of thorium. 

For short-term experiments, thorium-232 is considered radiologically inert since its half-life is so long. Therefore, the chemical toxicity of thorium was tested using this isotope. The low chemical toxicity of thorium was evidenced by the lack of initial systemic effects in patients injected with Thorotrast and in occupationally exposed workers. Animal studies also showed low toxicity (Guimaraes et al. 1955 Patrick and Cross 1948). Natural thorium (thorium-232) is toxic only after a latency period of 20-30 years, when the radiological effects are manifested. 

The radiological effects of thorium were examined by testing isotopes with shorter radioactive half-lives than thorium-232. No increased mortality was found in mice injected intravenously with 0.5 ml Thorotrast (3660 mg thorium-232/kg) (Guimaraes et al. 1955), or in dogs after intraarterial injection of thorium nitrate (476 mg thorium-232/kg), but the LDsofor intravenously- injected thorium-230 in rats was 42.7 mg thorium/kg (Boone et al. 1958). The toxic effects of thorium were attributed to radiological and not chemical effects (Boone et al. 1958). 

Following intravenous injection of Thorotrast in humans and animals, various malignancies were found, primarily liver cancers (latency period of 25-30 years), leukemia (latency period of 20 years), and bone cancers (latency period of about 26 years). Short-lived daughter products of thorium also resulted in the induction of bone sarcoma because of their short radioactive half-lives. Intravenous injection of thorium-228 resulted in dose-dependent induction of bone sarcoma in dogs (Lloyd et al. 1985 Mays et al. 1987 Stover 1981 Wrenn et al. 1986). At the highest administered level, the animals died from systemic radiological effects (e.g., radiation induced blood dyscrasia and nephritis) before the bone sarcoma could develop (Stover 1981 Taylor et al. 1966). A relationship was found between the amount of thorium-227 (half-life of 18.7 days) injected intraperitoneally and the incidence of bone sarcoma in mice (Luz et al. 1985 Muller et al. 1978). 

Neonatal animals have been found to absorb 20-40 times more thorium through the gastrointestinal tract than adult animals (Sullivan et al. 1980a, 1980b, 1983) indicating that children may be more susceptible to both the chemical and radiological effects of thorium than adults. 

The estimates of release of fission products from Windscale, which are inevitably subject to error, are not essential to the assessment of the radiological effects, which are based on local measurements of activity in milk and other foodstuffs, and in the thyroids of members of the public. 

There has also been speculation that there is a potential black market use of DU as a weapon for bioterrorism, or as part of a dirty bomb. However, a thorough evaluation of the toxicology of uranium indicates that DU is relatively inert, compared to other potential materials and organisms that could be used to make an effective bioterrorism weapon or dirty bomb. Indeed, the reason why DU may still be considered to be an excellent bioterrorism agent is the public perception that DU is a harmful chemical, even though the toxicology of the chemical and radiological effects are relatively mild. 

Lack of radiological effects (see Tables 2-1, 2-2, 2-3, and 2-4) in studies that used natural uranium is due to the low specific activities of natural and depleted uranium, which are 0.67 and 0.3 pCi/g, respectively. In comparison, the calculated specific activity for 97.5% enriched uranium is approximately 50 pCi/g. 

Table 2-8 shows the mass equivalents for natural and depleted uranium for radiation levels that caused potential radiological effects in rats exposed once for 100 minutes to airborne 92.8% enriched uranium with an estimated specific activity of 51.6 pCi/g (Morris et al. 1989). These mass equivalent values for natural and depleted uranium for the minimal concentration of radioactivity that is expected to induce potential radiological effects are well above levels that would be expected to be inhaled or ingested. In addition, the mass equivalents for natural and depleted uranium for potential radiological effects are 3,600 and 76,500 times higher, respectively, than the occupational exposure limits (short-term exposure) recommended by the National Institute for Occupational Safety and Health (NIOSH 1997). Therefore, MRLs for uranium based on studies that used enriched uranium are inappropriate. 

Ehrlich R, Lilis R, Chan E, et al. 1992. Long term radiological effects of short term exposure to amosite asbestos among factory workers. Br J Ind Med 49 268-275. 

Unstable decay products of thorium may exceed their parent in their importance both in occupational and nonoccupational environments as contributors to the radiation dose. They produce only radiological effects. In view of the lesser importance of thorium decay products as compared to the uranium decay chains, this aspects are dealt with later (see Chapter 26.2, Section 26.2.6.3). 

R. Mukherjee and J. Mircheva, Radiological effects of low-level radiation and cancer risks, IAEA Bulletin 2 (1991) 32. 

Radioiodine is also identified as one of the most important fission products that can be released from nuclear facilities, particularly under accident conditions, in terms of its radiological effects on the environment, especially human exposure. A large amount of I delivered to the thyroid almost always leads to hypothyroidism, because of permanent radiation-induced destruction of thyroid cells. The use of potassium iodide (KI) helps in preventing such harmful effects. 

F. A Description of Some of the Radiological Effects of a Large Release of... 

The committee and its Los Alamos consultants were not unmindful of the radiation effects of the atomic bomb—its most significant difference in effect from conventional high explosives—but worried more about radiation danger to American aircrews than to the Japanese. Dr. Oppenheimer presented a memo he had prepared on the radiological effect of the gadget.. .. The basic recommendations of this memo are (1) for radiological reasons no aircraft should be closer than 2 /6 miles to the point of detonation (for blast reasons the distance should be greater) and (2) aircraft must avoid the cloud of radio-active materials. ... 

It Is believed that there are several options available for minimising the content In the activated concrete of materials, particularly steel, which are difficult to remove either for physical reasons or because of radiological effects. There may also be ways of altering the concrete mix to enhance Its shielding properties. These aspects are discussed In detail In Section 6.3 of the report. 

A safety envelope is provided that basically encloses the containment, with the exception of the areas above the containment top slab and the drywell head. The containment and safety envelope in conjunction with other safety-related features limit radiological effects of design basis accidents to less than the prescribed acceptable limits. 

Due to the low speeific radioactivity of natural uranium (about 1 Ci per 3 metric tons or 81 ng U-238 per Bq Frame 4.3), the main health effects are through its chemical toxicity. However, in some cases, the radiological effects may be dominant, like in the case of exposure to enriched uranium or when insoluble uranium compounds enter the body through inhalation or injury and are retained in the body for an extended period. The fact that the decay products of uranium (progeny) are also radioactive may enhance the radiological health effects. 

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