Calibration of Radiometers for Mass Control of Incorporated 131I, 134Cs and 137Cs Nuclides with the Help of Volunteers

Abstract

Calibration of portable scintillation radiometers used for measurement of incorporated radionuclides in the bodies of inhabitants of territories contaminated due to the Chernobyl accident was performed with the help of volunteers each of whom was administered per os 370 kBq of the ¹³⁴Cs and ¹³⁷Cs mixture. Whole-body measurements of volunteers were carried out over 20 days with different kinds of whole-body counters and various measurement geometries. Urine and faeces were collected daily; measurements with a beta radiometer and gamma spectrometer were made using the first seven days after the radionuclide intake. The caesium radionuclide content in each volunteer in the first seven days was determined as the difference between the administered and excrete amounts. The dependence of calibration factors upon some parameters of the human body and constitution, on NaI crystal size, and ratio of ¹³⁴Cs to ¹³⁷Cs were investigated. It was shown that caesium was homogeneously distributed over a body only 20 days after the intake. The inhomogeneity of its distribution during the first few days can cause considerable errors in the results of in vivo measurements by means of simple radiometers. Calibration of the radiometers for ¹³¹I in the thyroid was done with the help of people who were administered iodine for diagnostic purposes. The technique for ¹³¹I determination in the thyroid in the presence of interfering radiation radiation from caesium radionuclides distributed homogeneously over the human body is presented. As a result of the investigation, a technique for rapid determination of ¹³⁴Cs and ¹³⁷Cs content in the human body was developed. More than 300,000 measurements have been made with this technique in the contaminated areas of Russia, following the Chernobyl accident.