Year
2019
Abstract
The development of new types of detectors and the increased performance of the electronics have paved the way for developing advanced systems for the measurement and identification of radioactive material that can be involved, for example, in illicit trafficking. Radioactive isotope identifiers are today commercially available. The performances of such devices are compliant with standards as the IEC 62327 Hand Held Instruments for the Detection and Identification of Radionuclides.This paper presents a new type of portable radioactive isotope identifier.This device, based on an organic liquid scintillator with excellent Pulse Shape Discrimination proprieties for the simultaneous detection of gamma rays and neutrons, detects radioactive source as Special Nuclear Material, medical, industrial and NORM.The exclusive feature of this instrument is the identification of neutron sources with discrimination between fission sources like 252Cf and alpha-n type sources like Am-Be from Plutonium and Uranium through an innovative dedicated algorithm.Performed tests demonstrate the capability to trigger the neutron alarm and also to identify the source with a neutron emission rate four time lower than standard specification.Individual thresholds for neutron and gamma counts are calculated to allow detection with 95% detection probability for a dose rate on the front face of the scintillator of at least 50 nSv/h.Alarms are triggered separately when the respective rate exceed these thresholds.The electronics is equipped with two analog inputs and two high voltage power supplies in a small form factor thus becoming an enabling technology for higher performance yet portable radioactive isotope identifier devices, which can include more detectors and perform data fusion analysis.A second detector enables also thermal neutron detection. In fact, a cutting-edge technology detector has been tested. NaI doped with Lithium can detect both gamma and thermal neutrons maintaining the standard gamma spectroscopy resolution of a NaI detector but adding the capability to count the thermal neutrons. The added benefit of thermal and fast neutron detection is the possibility to better detect shielded neutron sources. Moreover, by replacing the NAIL with a CeBr3 scintillator allows also the calculation of Pu and U enrichment grade through characteristic gamma emission line.