Investigation of Silicon Detectors to Improve In Vivo Monitoring of 239Pu After Accidental Intakes

Measuring in vivo contamination remains a difficult task for some actinides such as 239 Pu due to the high absorption of low energy X rays associated with alpha decay. X rays and low energy gamma ray methods based on high purity germanium detectors are most suitable in view of their quasi-ideal combination of high energy resolution, typical of semiconductor materials, and high efficiency curve due to the high atomic number of Ge. Their application, however, is often limited for practical reasons relating to the need to cool the HPGe crystal to liquid nitrogen temperature during the operation, and to the minimum size of the crystal, which increases the background response of the detector. The investigations carried out with passive implanted planar silicon (PIPS) detectors, presented as a viable alternative to HPGe detectors for some applications, are summarised here. Taking into account the steeper efficiency curve of silicon relative to energy, the quantitative information obtained using silicon prototypes shows which new developments may be most beneficial.