The Auger cascade and therapeutic applications of 125I.

The Auger cascade consists of low-energy electrons which are emitted instead of characteristic X-rays when a vacancy in an inner electronic shell is filled. Such atomic vacancies are produced by orbital electron capture, internal conversion, and the photoelectric absorption of photons. The relative abundance of Auger electrons and their decrease with increasing atomic charge (Z) is explained. For iodine (Z = 53), about 30% of the energy is carried by Auger electrons and thus is dissipated locally. As the concept of average dose cannot always be applied to electron capture decay in cellular components, microdosimetric parameters, applied separately to each of the distinct types of low energy radiations involved, seem more appropriate. The development and applications of the relevant microdosimetric concepts are reviewed briefly. The approach explains the high biological effectiveness of 125I in different and unrelated systems, such as DNA molecules and the thyroid gland. The effects of 125I on thyroids of humans and experimental animals were compared to those produced by 131I by the Glasgow and the Beilinson groups. The experience of these teams in applying therapeutic doses of 125I in order to control thyrotoxic patients is evaluated.

Long-lived radionuclides in food: 90Sr and 137Cs in the Israel diet.

Routine monitoring of Strontium-90 and Cesium-137 levels in the main classes of food consumed in Israel has been carried out for a number of years. Calculations have been made of the intake of these isotopes by various groups in the Israel population using Food Consumption Survey data made available by the Israel Central Bureau of Statistics. More detailed analyses have been carried out to calculate the exposure of groups selected on the basis of demographic, economic and family-size criteria. This was carried out in an attempt to detect "critical groups" in the population who might be overly exposed. Results of these data indicate that in the case of Israel the monitoring of a single food item such as milk or the extrapolation of local fallout data cannot be relied on to give an estimate of radionuclide exposure through food. The relation between high consumption groups and the intake of "average" consumers is discussed in detail and the use of the statistical models developed in these studies for the estimates of radionuclide exposure during periods of high fallout levels which occurred in the past and possible applications with regard to other environmental contaminants is discussed.