NaTIF Radiation Portal Monitor performances optimization by means of multi-parametric analysis
Abstract
NaTIF (NaIL-based Threats radIation emitters Finder) is a patented new generation Radiation Portal Monitor (RPM) under current development in CEA LIST Institute. This technology aims at proposing a RPM to be deployed in highly frequented civil zones and national borders in order to ensure their control and protection against radiological and nuclear threats. The technology is based on the use of inorganic scintillators [NaI:Tl(6Li)], denoted hereafter as NaILTM. These detectors are price attractive and relevant for the identification of both radiological and nuclear signatures. Indeed, in terms of gamma spectrometry, the state of the art shows that these scintillators have an energy resolution close to classical NaI:Tl detectors close to 6-8% for the Cs-137 gamma ray at 661.7 keV. Moreover, those scintillators are doped with 6Li. This allows to detect gamma and neutron signatures and to separate each contribution by means of Pulse Shape Discrimination (PSD), with important discrimination capabilities given by a Figure of Merit (FoM) estimated at 3.8 in the scope of the current work. The small scale RPM currently studied mainly consists in the combination of two NaILTM detectors with three EJ-200 plastic scintillators [Fig.1A]. Each detector has an active scintillation volume of 1000 cm3. The use of EJ-200 detectors enhances the neutron sensitivity of the global RPM as they are used as neutron detectors as well as moderators. All detectors are biased independently using a DT8033M CAEN® power supply delivering both positive and negative high voltage. Associated output signals are collected and treated with a CAEN® DT5730SB digitizer coupled to CoMPASS software. Signal processing is done according to the settings implemented on the software such as: Charge integration short and long gates for PSD computations, Constant Fraction Discrimination (CFD) set of parameters, signal smoothing and corresponding threshold, etc. The present study aims at optimizing technical and operating performances in accordance with specifications for the global RPM, using multi-parametric analysis. This, firstly done on NaILTM detection systems, includes the tuning of hardware parameters such as the high voltage and associated gain and threshold with the software set parameters of CoMPASS in order to minimize the energy resolution [Fig.1B], to maximize the FoM for gamma/neutron discrimination [Fig.1C], and to detect the low energy gamma rays of interest emitted by radiological threats such as the 59.5 keV gamma rays from Am-241 [Fig.1D]. Reported results associated to parametric performances optimization were processed in a laboratory environment with Cs-137, AmBe, and Am-241 radiological simulants.
Keywords
instrumentation
nuclear instrumentation
ionizing radiation
radioactivity
NaIL-based Threats radIation emitters Finder (NaTIF)
patent
Radiation Portal Monitor
monitoring
detector
highly frequented civil zone
national border
radiological threat
nuclear threat
inorganic scintillator
isotope identification
radiological signature
nuclear signature
gamma spectrometry
spectrometry
gamma-rays
energy resolution
doping
neutrons
neutron signature
Neutron-gamma discrimination
Pulse Shape Discrimination (PSD)
discrimination capability
Figure of Merit (FoM)
plastic scintillator
active scintillation volume
moderator
high voltage
signal processing
spectrum analysis
signal collection
DT5730SB digitizer
CoMPASS
Charge integration
short gate
long gate
Constant Fraction Discrimination (CFD)
signal smoothing
signal threshold
performance optimization
technical optimization
multi-parametric analysis
tuning
low energy gamma-rays
137Cs
AmBe
241Am
radiological simulant