Year
2011
Abstract
A 6LiF:ZnS(Ag) based technology has been developed as a replacement for He-3 detectors in Radiation Portal Monitors (RPMs). An early prototype having an active area of 1000cm2 has been independently tested at the Pacific Northwest National Laboratory [1]. These tests reported a sensitivity comparable with that of a 1m long, 5cm diameter, 3 atmosphere He-3 proportional counter and an ability to operate with a full-field gamma-ray dose-rate of 100mR/h (2.58x10-5c/kg/h in air). Subsequent developments have included scaling the detector technology to provide both smaller (200 cm2) and larger-area detectors (1131 and 1740 cm2) and using multiple detectors in combination. For example, the sensitivity and gamma-ray rejection performance of a neutron detection module (NDM) intended for use in an RPM which included 4x1131 cm2 detection elements, has been verified by the UK Health Protection Agency [2] as providing a sensitivity of between 4.05±1.10 counts per second per nano-gram of 252Cf. This was measured using a calibrated source encapsulated within 1mm steel, 6.4mm lead and surrounded by 25mm of HDPE. This detector also simultaneously demonstrated a gamma-ray sensitivity less than 7.94 x 10-8. The Gamma Absolute Rejection Ratio for neutrons (GARRn) [3] of the detector varied by less than 5% as the gamma-ray dose-rate increased from zero to 200 mSv/h (20mRem/h). This paper will introduce the technology and discuss its application as a He-3 replacement for Nuclear Security and Physical Protection.