Portal, freight and vehicle monitor performance using scintillating glass fiber detectors for the detection of plutonium in the Illicit Trafficking Radiation Assessment Program

Neutron-sensitive scintillating glass fiber sensors provide several advantages over neutron-sensitive gas-tubes for plutonium detection and surveillance. Large area detectors and higher effective neutron capture density provide significant improvements in sensitivity versus cost. The glass sensors offer a wide dynamic counting range, fast response time, no transport hazard, greater operator safety and lower micro-phonic susceptibility relative to conventional ³He and ¹⁰BF₃ sensors. We report on the testing methods used in Illicit Trafficking Radiation Assessment Program and our experience in evaluating the performance of the portal, freight and vehicle monitors for customs applications employing these new sensors. Results of false and real alarm tests and distribution tests are presented and compared to previous Monte Carlo and first principle calculations. These earlier calculations determined the detection limits for neutron glass panels used for continuous monitoring of special nuclear materials. Assumptions used in the model assumed a nominal background count rate for neutrons of 0.010 n·cm^-2·s^-1, an intrinsic neutron efficiency of 20% and an alarm set point of 5.2 sigma representing one false alarm per month. Measured neutron data taken with ²⁵²Cf and several gamma ray sources confirm the calculated data. Calculations assume an unshielded source and are conservative because they do not include environmental improvements in neutron economy. The results demonstrate that these systems are capable of reliably detecting special nuclearmaterials (SNM) and other radionuclides within a few seconds.