Radiocontamination of the environment and its effects on the mother and fetus—III: Part II—Retention of cesium 137 by pregnant women, placentae and infants

Abstract

The total body counter employed in this study has bccn presented elsewhere cz~) and consists of four large plastic scintillator units, each block measuring 50/50/15 cm, placed at 30 cm over a Lucite plate counting bed at equal distances. A similar arrangement with four other scintillation blocks was placed 10 cm below the counting plastic bed. Each plastic scintillator block was optically linked with a photomultiplicr of 5 in. dia; the ratio between the photocathodc area of the photomultiplicr and the scintillation block is about 5 per cent, which diminishes the efficiency of the system. The combined output from the units reached a cathode follower and wcrc mixed and passed to a linear amplifier. The output of the amplifier was further fed into three single-channel analyzers with associated sealers. For the potassium 40 peak (1455kcV) two singlechannel analyzers selected the pulse, each of the analyzers being set at half of the peak; the sum of the two pulses was attributed to 40 K, while the third analyzer was adjusted to the photopeak of a~Cs. The counting system was calibrated by body phantoms of a wide variety of lengths and weights, filled with distilled water containing a known amount of KC1 or 137Cs. The calibration constants were found to show a linear relationship with the body weight between 36 and 70 kg; the correction was made for the weights of the subjects measured. The sensitivity of the instruments was controlled by counting 18~Cs point sources. Fifteen minutes counts wcrc made on each subject; the background level was periodically measured throughout the day for I hr. The data wcrc processed by a digital computer (Burroughs-5500): with a counting time of 15m in, the statistical accuracy (q-a) was respectively -4-1.5 and 4-65 per cent for 40 K and 137Cs, assuming a body burden of 150 g stable potassium and 10 nc aXVCs. However, the absolute uncertainties arising from calculation errors may amount to 4-5 per cent.