Evaluation of Scintillator Detection Materials for Application within Airborne Environmental Radiation Monitoring

In response to the Fukushima Daiichi Nuclear Power Plant accident, there has occurred the unabated growth in the number of airborne platforms developed to perform radiation mapping—each utilising various designs of a low-altitude uncrewed aerial vehicle. Alongside the associated advancements in the airborne system transporting the radiation detection payload, from the earliest radiological analyses performed using gas-filled Geiger-Muller tube detectors, modern radiation detection and mapping platforms are now based near-exclusively on solid-state scintillator detectors. With numerous varieties of such light-emitting crystalline materials now in existence, this combined desk and computational modelling study sought to evaluate the best-available detector material compatible with the requirements for low-altitude autonomous radiation detection, localisation and subsequent high spatial-resolution mapping of both naturally occurring and anthropogenically-derived radionuclides. The ideal geometry of such detector materials is also evaluated. While NaI and CsI (both elementally doped) are (and will likely remain) the mainstays of radiation detection, LaBr3 scintillation detectors were determined to possess not only a greater sensitivity to incident gamma-ray radiation, but also a far superior spectral (energy) resolution over existing and other potentially deployable detector materials. Combined with their current competitive cost, an array of three such composition cylindrical detectors were determined to provide the best means of detecting and discriminating the various incident gamma-rays

Theoretical description of deformed proton emitters: nonadiabatic coupled-channel method

The newly developed nonadiabatic method based on the coupled-channel Schroedinger equation with Gamow states is used to study the phenomenon of proton radioactivity. The new method, adopting the weak coupling regime of the particle-plus-rotor model, allows for the inclusion of excitations in the daughter nucleus. This can lead to rather different predictions for lifetimes and branching ratios as compared to the standard adiabatic approximation corresponding to the strong coupling scheme. Calculations are performed for several experimentally seen, non-spherical nuclei beyond the proton dripline. By comparing theory and experiment, we are able to characterize the angular momentum content of the observed narrow resonance.Comment: 12 pages including 10 figure

Comparison of the pulse shape discrimination performance of plastic scintillators coupled to a SiPM

We report on the pulse shape discrimination (PSD) performance of plastic scintillators manufactured by Eljen Corporation and Amcrys. In this study we investigate the fast neutron and gamma performance of the plastic scintillators when coupled to the SensL J-series silicon photomultiplier (SiPM) and read out with fast waveform digitisers with an ADC resolution of 14-bits and a sample rate of 500 MS/s. The investigation observes a significant PSD performance increase for the SensL J-series SiPM in comparison to the previous C-series, and also for the latest variants of plastic scintillator from both suppliers. Analysis was performed using a Synchronous Charge Integration Pulse Shape Discrimination (PSD) algorithm which was applied to data acquired from a mixed fast neutron/gamma radiation field from an AmBe neutron source. The collected pulses were processed offline with the energy and PSD parameters calculated. The quality of the PSD performance was characterised by a common figure of merit (FoM). The best n- separation was found by the newer Eljen EJ-276 scintillator with a FoM value of 3.03 ± 0.03 at an energy of 1.5 MeV gamma equivalent. The Amcrys UPS-113NG material achieved a FoM value of 2.60 ± 0.04.</p

Exploration of Fourier based algorithms and detector designs for pulse shape discrimination

We investigate the performance of Fourier-based neutron/gamma Pulse Shape Discrimination (PSD) algorithms applied to plastic scintillators that are coupled to silicon photomultipliers (SiPM). The detector acquired data from a mixed fast neutron and gamma field which was emitted from an AmBe source. Pulses produced from the detector were fully digitised for off-line analysis with the algorithms. We describe the performance of two Fourier-based PSD algorithms, Fourier Gradient Analysis (FGA) and Fourier Area Analysis (FAA), and compare their performance to the Charge Comparison Method (CCM). To compare the algorithms’ PSD performance the figure of merit (FoM) was calculated at various energies for each of the algorithms. The CCM analysed the pulses in the time domain whereas the other two algorithms processed the pulses within the frequency domain. Moreover, the detector was tested with different acquisition record lengths, in order to determine any impact on algorithm performance. It was determined that the FAA algorithm provided the best overall performance achieving a FoM of 1.57(1) at 1 MeVee with a 1.6 µs record length. Furthermore, the detector was tested using different load resistors which allowed the decay time of the pulses to be optimised. The influence of SiPM pulse decay time on the performance of the PSD algorithms is also presented

A digital pulse shortening method for the mitigation of pulse pile-up effect in scintillation radiation detectors

The pulse pile-up effect can significantly degrade the spectroscopic performance of scintillation radiation detectors at high counting rates. This paper reports on a digital pulse processing method for shortening the duration of scintillation pulses, thereby alleviating the pulse pile-up effect. The method operates based on replacing the decay-time constant of the scintillation pulses with a shorter decay-time constant. The details of the digital algorithm are presented and the performance of the method at a high counting rate of 795 kHz is experimentally examined with a NaI(Tl) detector. The effects of the pulse shortening on the spectroscopic performance of the system are also discussed

Investigation into the potential of GAGG:Ce as a neutron detector

In this work we investigate the potential use as a thermal neutron detector of cerium-doped gadolinium aluminium gallium garnet (GAGG:Ce) coupled to a silicon photomultiplier (SiPM). The response to thermal neutrons has been measured, with two strong low energy neutron-indicative peaks clearly identifiable below 100 keV and additional γ peaks at higher energies. The neutron-related peaks are produced by a combination of contributions from excited states of the two isotopes 156Gd and 158Gd which can be clearly resolved in our GAGG scintillation detector. In particular, two peaks due to neutron-induced γ-ray emission are observed at approximately 82 keV and 260 keV, with best achieved energy resolutions of 24.1 ± 0.2% and 22.7 ± 0.7% respectively. Three different scintillator volumes (0.1 cm3, 0.4 cm3, and 1 cm3) were investigated and the respective results for each configuration will be presented. Our findings show that a GAGG-SiPM based detector can be used as a compact, efficient thermal neutron detector in a low γ-ray contamination environment.</p