Standardization requirements for the in vivo counting techniques of gamma - and soft X-ray radionuclides

The techniques for the in vivo counting of the internal body burden of radionuclides for radiation protection purposes can be divided into two broad categories according to the energy of the measured radiation: (a) measurement of internal contamination due to radionuclides emitting gamma-rays with energies above 100 keV; (b) measurement of internal contamination due to radionuclides emitting soft gamma-or X-rays with energies below 100 keV. The subdivision into two categories is mainly dictated by the many different problems encountered in counting low levels of X-ray emitting radionuclides (such as plutonium isotopes) in man. A mandatory requirement to obtain a reasonable sensitivity of the counting systems for both categories requires a sensible reduction of the normal background due to cosmic rays and to the natural radioactivity present in the human environment (soil, building materials, air, etc).