Accidental radiation exposure

Table 22.7. Effects of accidental radiation exposure on man (approximate values).

Thousands of devices containing potentially dangerous amounts of radioactive material are used in the world. However, the safety record for the use of radioactive materials is incredibly good. As shown in Table 9.1 there are only about two deaths or serious injuries worldwide each year from accidental radiation exposure. This is because most countries have rules requiring that dangerous amounts of radioactive material (and chemicals) be carefully controlled at all times. 

The build-up of radicals in irradiated solids forms a method of estimating the absorbed dose of ionizing radiation. A standard used in EPR dosimeters is the amino acid alanine, in pellet form, which gives a linear relationship between radical signal amplitude and absorbed dose over several orders of magnitude. Where there has been accidental radiation exposure, the EPR of radicals in hydroxyapatite in tooth enamel has been used to estimate the absorbed dose. Irradiation of foods such as meat may be detected by radicals formed in bone. 

Models of radiation damage have been explored and are well developed. For many years, accidental releases of ionizing radiation have been universally feared. Alternatively, radiation has been used in controlled, defined amoimts as a therapy for certain tumors in both companion animals and humans. Taken together, all studies provide a cohesive and comprehensive picture of radiation toxicity. There are sufficient details of radiation effects to make credible estimates of risk resulting from radiation exposure (Harley 2001, 2008). 

The occupational, accidental, and wartime experiences have provided the basis for the estimation of risk to humans following radiation exposure. However, cosmic, cosmo-genic, inhaled, and in-body radiation deliver total body effective doses of 3 becquerel per year total effective dose. The average radon concentration indoors is 40 becquerel... 

Urine samples for bioassay are collected from workers who may have inhaled or ingested radionuclides or hazardous chemicals, either while routinely handling samples with higher radionuclide or chemical concentrations, or after accidental exposure. The samples are analyzed for the radionuclides or chemicals that may have been taken in by the worker and the measured concentrations are used to calculate radiation exposures or to compare to radionuclide or chemical concentration limits. The frequency of sampling for bioassay depends on the occurrences of exposure and the rate of turnover of the radionuclides or chemicals in the body. 

The exposure of an unborn baby to radiation is referred to as prenatal radiation exposure. This can occur when the mother s abdomen is exposed to radiation from outside her body. Also, a pregnant woman who accidentally swallows or breathes in radioactive materials may absorb that substance into her bloodstream. From the mother s blood, radioactive materials may pass through the umbilical cord to the baby or concentrate in areas of the mother s body near the womb (such a.s the bladder) and expose the unborn baby to radiation. 

Repair and alignment activities provide some of the best opportunities for accidental over-exposures. Every precaution should be taken to prevent these incidents. Several measures are listed below. Most of these should be made mandatory by the organization s written radiation safety policies. 

Chapters 25 and 26 discuss radiation protection and the effects of low dose radiation. Persons near or involved in an accidental criticality will receive high radiation exposure that can lead to death. Radiation protection involves the methods of protecting personnel and the environment from excessive radiation exposure. Low dose radiation is discussed to show that the impact of radiation from nuclear power operations is a small fraction of the radiation people receive each day. 

Wherever possible, ultraviolet radiation should be contained . If visual observation of any process is required, this should be through special observation ports transparent to light but adequately opaque to ultraviolet radiation. Where the removal of covers could result in accidental injurious exposures, interlocks should be fitted which either cut the power supply or shutter the source. Protection is also achieved by increasing the distance between source and person, covering the skin and protecting the eyes with goggles, spectacles or face shields. 

The air diaphragm piunp, being a fiilly contained pump, eliminates the possibility of accidental loss of radioactive fluid due to seal leakage, thereby minimising the risk of public or operator radiation exposure from wastewater transfer. 

Occupational, accidental, and wartime experiences have provided the basis for the estimation of risk to humans following radiation exposure however, cosmic. 

AH x-ray equipment must be periodically inspected and the output monitored and caUbrated to minimize the chance of accidental overexposure. Another concern involves radiation accumulation by medical personnel operating x-ray equipment. Although the dose to any one patient may be low, the accumulated dose to a clinician performing multiple exams each day over the course of a year is great. Therefore, personnel working with x-ray equipment must take precautions constandy to minimize and monitor exposure. Lead aprons and film badges are used to minimize exposure and to monitor accumulated dose, respectively. 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

It has been known for many years that homolytic fusion of the 0-0 bond in H2O2 will yield the hydroxyl free radical OH. This may be produced by exposure of H2O2 solutions to heat or ionising radiation and hence may be formed, for example, after accidental or therapeutic exposure to radiation (e.g. during cancer therapy) ... 

Typical irradiation facilities consist of a process chamber containing the radiation source, some sort of conveyor systems to transport products inside and outside the shielding walls, and sophisticated control and safety systems. Irradiation facilities are built with several layers of redundant protection to detect equipment malfunctions and protect employees from accidental exposure. Technical details depend on the type of irradiation. Typical processing parameters are compared in Table 2 [7]. 

Larsen PR, Conard RA, Knudsen K. Thyroid hypofunction appearing as a delayed manifestation of accidental exposure to radioactive fallout in a Marshallese population. In Biological Effects of Ionizing Radiation 1. Vienna International Atomic Energy Agency, 1978 101. 

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