The in vivo detection of low energy photon emitters in radiation protection and in nuclear medicine. A new philosophy for new needs in in vivo counting

A new methodology of whole-body counting adapted to the detection of radionuclides emitting low energy photons is described. This modification in the counting philosophy can be useful because the use of new radionuclides in nuclear medicine and the recycling of plutonium in reactor fuel materials require new techniques. They are based on the use of room temperature detectors (silicon and CdZnTe diodes principally), on long duration counting performed out of shielding rooms and on special detector mountings such as a jacket allowing the detectors to be held in a fixed position on the measured organ. The counting can be done without shielding rooms when the detector geometry is adapted to the investigated photon energy so that the control of the intake can be done soon after the suspected contamination accident. The characterisation of the background is of primary importance in the counting of low energy photons and is described by considering the required detection limits and the effect of the counting geometry on the accuracy. The detector position, the bias voltage, the detector thickness and the shielding environment are described on the basis of experimental results. The study of metabolism is a new application for these designs and techniques.