A Measurement Technique for Trace Radioactivity Distributions in the Human Body by Using Gamma-Ray Spectra

A new technique is described to increase spatial resolution in the distribution measurement on amount of trace radioactivity in the human body by the response function method. The distribution is obtained by analysing the difference in gamma-ray spectra measured around the body, which contains information for not only unscattered gamma-rays, but also scattered ones within the body. Basic experiments involving the measurement of two-dimensional radioactivity distribution in a homogeneous acrylate block (40cmW × 20cmH × 50cmL) containing two 137Cs point sources (0.8 and 1.0 μCi) were made using gamma-ray counts measured by twenty 2" ϕ × 2" NaI (Tl) scintillators arranged on a circle, and the response function calculated by the Monte Carlo technique. The distribution on a 10 × 5 mesh division was successfully analysed with a relative error of less than ± 20% for a measuring time of 10 min. The mesh size was 4cm × 4cm, which was about one-half that possible when analysing only unscattered rays.