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Guidelines for radiation protection.

Guidelines for radiation protection originate from numerous federal, state, and local agencies. Webster defines a guideline as a line by which one is guided, especially as an outline (as by a government) of policy or conduct. Guidelines in radiation protection can be either mandatory or advisory. Regulations by federal, state, and local governments for the use of radioactive materials define operating practices. Adherence to these regulations is required by law and there are penalties for noncompliance. Regulations generally constitute the minimum requirements for good practice and are usually supplemented by less formal recommendations from regulatory agencies and advisory groups. The regulatory guides published by the Nuclear Regulatory Commission (NRC) and by radiation control groups of agreement states are intended to assist the user of radioactive material in maintaining compliance with regulations. These guides recommend good practice but are not mandatory in that the user can propose alternatives to the regulatory agencies to meet the regulations. Many groups serve in an advisory capacity in formulating reports and recommendations for the safe use of radioactive material. The most prominent and influential among these are the National Council in Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP). Often the recommendations of these advisory groups evolve into either regulatory guidelines or regulations for the use of radioactive materials. At the present time, the backbone of the Nuclear Regulatory Commission's regulations relating to the medical use of radionuclides, "Standards for Protection Against Radiation" (10CFR20) and "Human Use of Byproduct Material (10CFR35), are undergoing extensive review with major revisions anticipated within the very near future. These proposed changes could have a significant impact on the practice of nuclear medicine. The changes will have some influence on radiation safety practice as it relates to the radiation worker, the patient, and the environment.

Air Pollutants, Radioactive↗

Radiation protection at synchrotron radiation facilities.

A synchrotron radiation (SR) facility typically consists of an injector, a storage ring, and SR beamlines. The latter two features are unique to SR facilities, when compared to other types of accelerator facilities. The SR facilities have the characteristics of low injection beam power, but high stored beam power. The storage ring is generally above ground with people occupying the experimental floor around a normally thin concrete ring wall. This paper addresses the radiation issues, in particular the shielding design, associated with the storage ring and SR beamlines. Normal and abnormal beam losses for injection and stored beams, as well as typical storage ring operation, are described. Ring shielding design for photons and neutrons from beam losses in the ring is discussed. Radiation safety issues and shielding design for SR beamlines, considering gas bremsstrahlung and synchrotron radiation, are reviewed. Radiation source terms and the methodologies for shielding calculations are presented.

Electrons↗

Radiation protection.

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Radiation Protection↗

Combined radiation-protective and radiation-sensitizing agents. IV: Measurement of intracellular protector concentrations.

Radiosensitization of hypoxic V79 Chinese hamster cells by 0.5 mM misonidazole at approximately 0-4 degrees C is substantially enhanced by pretreating the cells overnight with 0.1 mM buthionine sulfoximine, which lowers the cellular glutathione content to 5% of control values (from 4 mM to approximately 0.2 mM). The enhanced sensitization is reversed by concentrations of exogenous cysteine that are much lower (0.02 mM) than the original glutathione content. Reduced Co-enzyme A affords reversal of the enhancing effect at concentrations of about 1 mM. Sodium ascorbate gives no protection at all even at concentrations of 2 mM. The intracellular concentration of the reducing agents was measured using a spin-through oil technique. There was no diffusion of Co-A (MW greater than 750) or ascorbate (excluded by charge) into the cells. In contrast, cysteine was rapidly concentrated by factors of 4-10, even at the low temperatures used. Extracellular ascorbate's inability to radioprotect argues against electron transfer across the cell membrane as a mechanism for radioprotection. This mechanism could have explained the ability of exogenous thiols to radioprotect in former studies using glutathione, and in the present studies using Co-A. The potential of cysteine to be concentrated by cells poses a problem in the interpretation of "exogenous protection" by non-diffusing thiols, since trace contamination by cysteine could lead to the actual protection observed. Cysteine could also be formed by exchange reactions of exogenous thiols with the disulfide of cysteine, present in all media formulations.

Animals↗