Development of a portable α-particle spectrometer

The detection of undeclared nuclear activities and the verification of declared nuclear facilities and materials are a matter of great concern worldwide. With the purpose of detecting and locating undeclared nuclear activities on site, a portable α-particle spectrometer was designed and built with a weight of 14 kg and a size of 30 cm × 30 cm × 30 cm that can be operated at normal temperature and with a maximum pressure of 1.0 torr. A feasibility study of this new portable α-particle spectrometer was conducted. The experimental results were compared with results from a laboratory α-particle spectrometry system. The 235U/238U ratio determined by the portable spectrometer was about 3.86%, while the laboratory spectrometry system gave the ratio of 3.90%. Their detection efficiencies were nearly identical for those two spectrometers. To improve the energy resolution of the portable spectrometer, a hexagonal-type collimator was designed by using GEANT4 and employed. With this collimator, the average full width at half maximum (FWHM) was enhanced from 29 keV to 24 keV . This study showed that the newly developed portable α-particle spectrometer, employing a small vacuum pump and minimized electronics, can be used for on-site measurement to detect and locate undeclared nuclear facilities and activities in a timely manner.