Assay of Skeletally Deposited Strontium-90 in Humans by Measurement of Bremsstrahlung

Abstract

An evaluation is presented of the accuracy and sensitivity with which skeletally deposited 90Sr can be assayed in humans by measurement of bremsstrahlung with whole-body counters of various designs. The yield of bremsstrahlung from skeletal deposits of 90Sr and equilibrated 90Y can be duplicated within about 10% using 90Sr sources in appropriate small plaster of paris and Lucite absorbers. The efficiency of measurement of bremsstrahlung produced in the body (counts/photon) can be calibrated probably within 5% by measurements on in-vivo tracer doses of the 7-ray emitting nuclides 47Ca or 85Sr. Under a particular set of measurement conditions the assay of 90Sr at the nanocurie level in normal people has been found to show a standard deviation of about 15 nC; this error results mainly from uncertainties in separating the bremsstrahlung component of the radiation spectrum from all other components.