Atomic energy review最新文献

In vivo neutron activation has opened a new era of research on the elemental composition of the human body. The techniques currently employed vary widely with respect to sources, moderators, site of activation and detection systems. Sources include cyclotrons, neutron generators and radioactive elements. Both partial body and total body neutron activation analysis (PBNAA and TBNAA, respectively) are commonly used to determine calcium levels. This review examines various aspects of the two techniques for delayed gamma neutron activation and the factors which affect the sensitivity of the measurements, uniformity of the neutron flux density, and the use of moderators. Portions of the body selected for partial body activation analysis are the hand, the arm and the trunk. Such measurement may be particularly useful for studying patients with diseases that affect various parts of the skeleton differently. However, to date, analyses based on TBNAA and PBNAA do not appear to favour one technique over the other. Comparison of the two techniques has to take into account a variety of factors: dose to the patient, cost reliability, availability of source, nature and cost of complementary facilities required, and the degree of expertise needed by the operating personnel. Neutron activation studies of body calcium have provided data useful for the diagnosis and management of a variety of metabolic disorders. Measurement of sodium, chlorine and nitrogen also appear to be useful clinically. A variety of clinical applications are discussed in this review. A recent development is prompt gamma neutron activation analysis, which can be used for the in vivo determination of cadmium in liver and kidney. Total body nitrogen (measured by prompt gamma neutron activation) and potassium measurements serve as indices of protein and muscle mass content, and hence are useful in assessing the roles of diet and nutrition in these body components.

In defining criteria for good protection against ionizing radiation, it is important to assess quantitatively the likely risk of any radiation exposure. The 'somatic' risks to the individual result mainly from induction of cancer in the organs irradiated, and these risks can now be estimated on the basis of numerous detailed epidemiological surveys of exposed human populations. Estimates of the risk of hereditary effects, from genetic changes induced in germ cells, are based largely on the frequency with which such effects are induced in other species. In both cases the risk at very low dose can be inferred using knowledge of the way in which radiation damage is caused in tissues. Coherent systems of radiation protection are based on a restriction of doses to the whole body and to individual organs, such that the induction of cancer and genetic harm is infrequent, and the threshold dose for causing other, 'non-stochastic', effects is not exceeded.

Recent developments in the field of the membrane biology of eukaryotic cells have revived relevant radiobiological studies. The supramolecular structures of membranes built up by the various chemical components that ensure certain functions and connections of the cells seem to react sensitively to ionizing radiations. Data concerning those radiation-induced alterations that reflect changes of such features and functions as surface charges, membrane-bound enzyme activities and receptor functions are reviewed. As the new concepts arising from the results obtained so far may have consequences in the theory and practice of radiation protection, a few areas are mentioned where the impact of the relevant accumulated knowledge might be expected to result in practical applications.

The findings and recommendations of an advisory group convened by the IAEA to give guidance relating to the development of IAEA projects involving radioassay are presented. The current status of radioassay services in different countries is reviewed; guiding principles relating to the organization of such services are affirmed, with particular reference to services in developing countries; the needs of services at various levels as regards accommodation, staff, equipment, supporting services and running costs, including minimum initial needs, are specified; operational problems are identified and indications given how they may be solved; facilities for training in radioassay are reviewed; finally, reference is made to IAEA activities in the field in question.

The history of radioactivity as an environmental contaminant is briefly traced. The basic principles concerning radiological protection and their application to the natural environment are reviewed. The relevance of these aspects of radiological protection philosophy and methodology to the control of other environmental contaminants is examined, especially the development and application of basic standards to waste disposal situations. It is concluded that many of the control procedures developed for radioactivity could be applied with advantage to other potential pollutants.

Twenty-two mineral elements are known to be essential for animal life. These are calcium, phosphorus, sulphur, potassium, sodium, chlorine, magnesium, iron, iodine, copper, manganese, zinc, cobalt, molybdenum, selenium, chromium, tin, vanadium, fluorine, silicon, nickel and arsenic. Naturally occurring and man-made dietary imbalances of many of these elements and their interactions with other minerals are described and their functions and requirements by farm animals are outlined. The nature and importance of metabolic interactions among the mineral elements are discussed and the important concept stressed that there is no single minimum requirement or safe tolerance of a particular mineral, but a series of such minimum requirements and safe tolerances depending on the extent to which other minerals with which it interacts is present or absent from the diet. Radioactive tracer elements are shown to be of great value in the determination of mineral nutrient availability to the animal and for following mineral metabolic movements in the body. They are also shown to have considerable potential for the diagnosis of mineral imbalances. Various in vivo and in vitro techniques, involving both radioactive and stable tracers developed for the early diagnosis of mineral deficiencies are described and the strengths and weaknesses of such techniques in comparison with standard biochemical tests, are discussed. The need for further critical studies with isotopic tracers in the detection and diagnosis of mineral imbalances is emphasized. The main types of biochemical criteria used in the diagnosis of mineral deficiencies and excesses are given, with appropriate examples of their use.