Radiation exposure control

Polymer films that are sensitive to light, x-rays, or electrons— known as photoresists—are nsed extensively to transfer the pattern of an electronic circuit onto a semiconductor surface. Such films must adhere to the semiconductor surface, cross-link or decompose on exposure to radiation, and nndergo development in a solvent to achieve pattern definition. Virtually all aspects of photoresist processing involve surface and interfacial phenomena, and there are many outstanding problems where these phenomena mnst be controlled. For example, the fabrication of multilayer circuits requires that photoresist films of about 1-pm thickness be laid down over a semiconductor surface that has already been patterned in preceding steps. 

Because exposure to radiation is a health risk, the administration of radioactive isotopes must be monitored and controlled carefully. Isotopes that emit alpha or beta particles are not used for Imaging, because these radiations cause substantial tissue damage. Specificity for a target organ is essential so that the amount of radioactive material can be kept as low as possible. In addition, an Isotope for medical Imaging must have a decay rate that is slow enough to allow time to make and administer the tracer compound, yet fast enough rid the body of radioactivity in as short a time as possible. 

Living cells are delicately balanced chemical machines. The ionization track generated by a nuclear particle upsets this balance, almost always destroying the cell in the process. Although the body has a remarkable ability to repair and replace damaged cells, exposure to radiation can overload these control mechanisms, causing weakness, illness, and even death. 

SC 57-16 Uncertainties in the Application of Metabolic Models SC 63 Radiation Exposure Control in a Nuclear Emergency SC 64 Radionuclides in the Environment... 

Carpenter et al. (1988) carried out a nested case-control study of cancer of the central nervous system among workers at two nuclear facilities located in Tennessee (United States). They identified 89 cases (72 males and 17 females) who had died between 1943 and 1979. Four controls, living at the time the case was diagnosed, were matched to each case. Job history records were scrutinized by an industrial hygienist to assess potential exposure to each of 26 chemicals or chemical groups. Toluene, xylene (see this volume) and 2-butanone (methyl ethyl ketone) were evaluated as one chemical group the matched relative risk was 2.0 (95% confidence interval (Cl), 0.7-5.5 n = 28) in comparison with unexposed workers. Almost all cases had had low exposure, according to the classification used and there was no dose-response trend. The authors stated that the relative risks w ere adjusted for internal and external exposure to radiation. 

For apprentices of 16-18 years of age who are training for employment involving exposure to radiation and for students of age 16-18 who are required to use sources in the course of their studies, the occupational exposure shall be so controlled that the following limits are not exceeded ... 

A dose of 64 mg/kg of 8-azaxanthine, given 2 h before exposure to radiation (700 rads), effected 24% survival whereas all the control mice died. ° l,3,9-Trimethyl-8-azaxanthine, at 350 mg/kg intraperitoneally, saved 25% of mice subjected to X-radiation lethal to all controls. 6-Amino-2-thioxo-, -2-methylthio-, and -2-ethylthio-8-azapurine had significant radioprotective properties, lost on quateraization. ... 

The high surface-to-volume ratio. In addition to an efficient illumination, in the case of photocatalytic reactions there is an efficient catalytic exposure to radiation and the reagent/catalyst contact is maximized [132, 133]. The small size of the channel also provides better control over variables such as temperature and fiow rates, due to the fast heat and mass transfer. 

Pattern exposure a pattern is generated by a mask or controlled radiation-beam steering, where the exposed material is degraded, chemically modified or crosslinked. 

Whatever the source of radiation used, the dose delivered to the biological samples is determined by the time of exposure to radiations. Thus the dose delivered by the radiation source must be measured with precision. Dosimetry can be performed with a ferrous sulfate solution (Fricke and Morse, 1927), thermoluminescent dosimeters, bleaching of films (Hart and Fricke, 1967), Perspex dosimetry (Berry and Marshall, 1969), or calibration with standard enzymes (Beauregard et al., 1980 Beauregard and Potier, 1982 Lo et al., 1982). In many laboratories, control enzymes with known D37 are added to protein preparations as internal standards so that any variation between experiments could be corrected for. Because of the better precision of dose rate in Gammacell irradiators, this precaution is not necessary. 

Restricted area means any area access to which is controlled by the licensee for purposes of protection of individuals from exposure to radiation and radioactive materials. Restricted area shall not include any areas used as residential quarters, although a separate room or rooms in a residential building may be set apart as a restricted area. 

During the sterilization procedure the radiation dose should be measured. For this purpose, dosimeters that are independent of dose rate should be used, giving a quantitative measurement of the dose received by the product itself. Dosimeters should be inserted in the load in sufficient number, and dose enough together to ensure that there is always a dosimeter in the chamber. Where plastic dosimeters are used, they should be used within the time-limit of their calibration. Dosimeter absorbances should be read within a short period after exposure to radiation. Biological indicators may be used only as an additional control. Radiation-sensitive colour discs may be used to differentiate between packages that have been subjected to irradiation and those that have not they are not indicators of successful sterilization. The information obtained should constitute part of the batch record. 

ALARA As low as reasonably achievable for controlling radiation exposure, aliquot A measured fraction of a solution. 

Larson H. 1980. Factors in controlling personnel exposure to radiations from external sources. In Plutonium handbook A guide to technology. Vol I, II. La Grange Park, IL- The American Nuclear Society, 845-857. 

With recent terrorist evenLs, many people have wondered about the possibility of a terrorist attack involving radioactive materials. People who live near but not in the immediate area of the attack may be asked to stay home and take shelter rather than try to evacuate. This action is called sheltering in place. Because many radioactive materials rapidly decay and dissipate, staying in your home may protect your from exposure to radiation. The thick walls of your home may block much of the harmful radiation. Taking a few simple precautions can help you reduce your exposure to radiation. The Centers for Disease Control and Prevention has prepared this fact... 

The RS shall include features to control radiation exposure to plant personnel from all core-derived radiation sources (including direct shine radiation). 

The RS shall control radiation sufficiently to facilitate total, collective occupational exposure to <100 man-rem/GW(e)-yr (Applies to normal operation and AOOs only). 

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