Direct Determination of 90Sr and 147Pm in Chernobyl Hot Particles Collected in Kiev Using Beta Absorption Method

Abstract

59 hot particles were collected in Kiev, Ukraine, in 1987. All but one were prepared from a moss carpet of 360 cm2 area. Radionuclide composition of the hot particles was investigated by gamma-spectrometry and beta absorption method. Pure beta emitters 90Sr and 147Pm were determined in 25 hot particles measuring the beta absorption curves of the hot particles with an end-window Geiger-Müller counter and decomposing the curves in order to obtain the contributions of 90Sr and 147Pm to the total beta counting rate. All but one of the hot particles were found to be the debris of the fuel. The activity ratio 90Sr:l44Ce was 0.052 in good agreement with theoretical calculations on core inventories. This means that strontium behaved as a nonvolatile element in the process of the formation of the hot particles investigated. The activity ratio 147Pm:144Ce was 0.078 which is half of the theoretical result. Although 147Pm is considered to be a refractory nuclide, it seems that significant part of 147Pm went to the homogeneous fraction of the general fallout. The surface density of hot particles (of higher than about 50 Bq activity) was about 1,600 m(-2) and that of the activities of the nuclides 90Sr, 106Ru, 134Cs, 137Cs, 144Ce and 147Pm as components of hot particles was 12.2, 54.3, 5.9, 9.7, 234 and 18.3 kBq m(-2) (activity values counted for 26 April 1986), respectively, in downtown Kiev city in 1987.

Absorption method for determination of pure beta-emitters in samples containing more than one beta-emitter

“…Further details on the collection and preparation of the samples can be found in previous papers. [1][2][3][4] t-counting and y-ray spectrometry An end-window "pancake" GM tube (type 73118, LND Inc., USA) was used in both applications for 13-counting. The diameter and the thickness of the mica window of the tube were 45 mm and 1.75 mg/cm 2, respectively.…”

“…4 For the evaluation of the absolute activities, the peak areas have been corrected also for the known interferences from y-lines of other isotopes.…”