Low energy gamma- and X-ray measurements by means of Compton suppression technique for safeguards environmental samples

Abstract

For analyzing ultra-trace amounts of nuclear materials in safeguards environmental samples, JAERI constructed a clean room facility. To eliminate the samples with excessive amounts of radioactive materials from the facility, that is the screening, the authors need to roughly estimate actinides and radioisotopes by non-destructive analysis. In this estimation, it is very inefficient to precisely measure the actinides by using HPGe detector because the intensities of the actinides' gamma-rays are generally low and their photopeaks (mostly below 200 keV) are severely interfered by Compton continuum caused by gamma-rays of fission products etc. within the samples. For suppressing Compton scattering signals with the energy less than several hundreds of keV, the authors have examined the feasibility of planar HPGe-LEPS and “short” coaxial low-energy HPGe detectors which were symmetrically surrounded with Nal(Tl) Compton suppressor detectors.In preliminary examination by measuring 137Cs standard source, background level was reduced by a factor of about 2 in the energy range from 50 to 400 keV.