N2D1  Scintillator Readout Methods

Tuesday, Nov. 3  16:30-18:10  Town and Country

Session Chair:  Chuck Melcher, Univ Tennessee, United States; Roger Lecomte, Universite de Sherbrooke,

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(16:30) N2D1-1, Design and Performance of a Compact Cs2LiLaBr6(Ce) Neutron / Gamma Detector Using Silicon Photomultipliers

P. R. Menge1, J. Lejay2, V. Ouspenski2

1Saint-Gobain Crystals, Hiram, OH, US
2Saint-Gobain Recherche, Aubervilliers, France
CLLB crystal scintillator is showing great potential as a radiation detection material with excellent energy resolution for gammas, sensitivity to neutrons, and the ability to separate the two using pulse shape discrimination. Experiments have been performed testing this material using silicon photomultipliers for creation of compact, easily-portable detectors for dual gamma ray spectroscopy and neutron detection. Pulse shape discrimination in CLLB is achieved by analyzing the scintillation pulse decay on the time scales of >1 micro-s. This feature enables the silicon photomultipliers to achieve acceptable discrimination, since the sensors do not need to detect fast changes associated with other discrimination signatures such as core-valence luminescence. Experiments have been conducted attempting to maximize performance by varying crystal shape, cerium concentration, discrimination algorithms, and silicon photomultiplier type and placement position. A disk of CLLB (diameter = 52 mm, thickness = 6 mm, 6Li enriched) coupled to a 6x6 mm2 silicon photomultiplier can achieve 6.0% gamma ray energy resolution at 662 keV, and 74% thermal neutron detection efficiency with a high pulse shape discrimination figure-of-merit of >1.9.

(16:50) N2D1-2, Neutron and Gamma Detection with a CLYC Crystal in a Phoswich Configuration with Other Inorganic Scintillators

G. Hull, M. Josselin, B. Genolini, I. Matea, D. Verney

Institut de Physique Nucleaire d'Orsay, IN2P3-CNRS, Université Paris Sud 11, Orsay, France
We tested the detection performances of a CLYC crystal when optically coupled to, in turn, LaBr3:Ce, CeBr3, SrI2:Eu and BGO scintillator, in a phoswich configuration, for the R&D of a neutron and gamma detector for application in nuclear physics studies. The interest of this work is to investigate the feasibility of a compact, solid-state detector as an alternative to the commonly used liquid scintillators or 3He gas proportional counters for the detection of neutrons. The ultimate goal will be to associate the phoswich with HPGe detectors in compact geometry to measure the energy of the beta-delayed neutrons, with good efficiency, in coincidence with gamma rays from exotic sources produced at present or next generation radioactive ion-beam facilities such as ALTO or SPIRAL2. We were interested in evaluating the effect of coupling two scintillators while maintaining the possibility to exploit their appealing properties (n detection/high light yield/high stopping power). In this communication we will report on the study of the light yield and energy resolution of elpasolite-based phoswich scintillators when irradiated with standard gamma ray and neutron sources. We will present as well the response of the phoswich detectors to neutrons in the energy range between 0.5 to 12 MeV. These results are the outcomes of an in beam campaign at the LICORNE inverse kinematics neutrons source facility, recently developed at ALTO.

(17:10) N2D1-3, Bismuth-Loaded Plastic Scintillators for Gamma Spectroscopy

N. J. Cherepy1, R. D. Sanner1, T. M. Tillotson1, H. P. Martinez1, P. R. Beck1, E. L. Swanberg1, S. A. Payne1, C. R. Hurlbut2

1Lawrence Livermore National Laboratory, Livermore, CA, USA
2Eljen Technology, Sweetwater, TX, USA
Standard commercial plastic scintillators are limited in use for gamma spectroscopy, due to their low Z, resulting poor photopeak efficiency. We are working on fabrication of transparent plastic scintillators based on polyvinyltoluene (PVT) with high loading of bismuth metallorganics for gamma spectroscopy. When activated with Iridium complex fluors, PVT scintillators containing 22 wt% bismuth metal provide energy resolution of <10% at 662 keV, while large-size bismuth plastics activated with standard singlet fluors provide R (662 keV) <15%. We demonstrate the performance of a phoswich detector employing a 6Li phosphor coating on a bismuth plastic activated with standard singlet fluors, allowing low-cost gamma spectroscopy and neutron detection. For scintillator geometry, cylindrical and slab shapes are being studied to identify the best configuration for scaleup and demonstration in radiation portals.

(17:30) N2D1-4, Exploring and Comparing the Neutron Anisotropy Across Organic Crystal Scintillators

P. Schuster

Nuclear Engineering, UC Berkeley, Berkeley, CA, USA
Organic crystal scintillators serve as valuable radiation detectors in nuclear security applications, providing excellent scintillation characteristics and neutron-gamma discrimination. Their performance in neutron detection is limited by a directional dependence: the light output and pulse shape vary as a function of the direction of the proton recoil with respect to the crystal axes. The directional dependence has been investigated via measurements that show that 1) the magnitude of the effect varies with energy and material, 2) the variation in light output and pulse shape are not coupled, and 3) gamma-ray and muon interactions are not subject to the directional dependence. The effect has been characterized for 14 MeV and 2.5 MeV proton recoil interactions in several materials. A comparative analysis of the effect across materials has been done to generalize observations. These characterizations provide insight into the mechanism that produces the anisotropy, and provide key performance information to potential users as to whether these materials are suitable for their application.

(17:50) N2D1-5, SrI2(Eu) Handheld Gamma Spectrometer Optimization

P. R. Beck1, N. J. Cherepy1, S. A. Payne1, S. L. Hunter1, E. L. Swanberg1, P. A. Thelin1, S. E. Fisher1, K. S. Shah2, R. Hawrami2, A. Burger3, L. A. Boatner4, M. Momayezi5, K. T. Stevens6, M. H. Randles6, D. Solodovnikov6

1Lawrence Livermore National Laboratory, Livermore, CA, USA
2Radiation Monitoring Devices, Watertown, MA, USA
3Fisk University, Nashville, TN, USA
4Oak Ridge National Laboratory, Oak Ridge, TN, USA
5Bridgeport Instruments, Austin, TX, USA
6Northrop Grumman SYNOPTICS, Charlotte, NC, USA
Abstract We are developing a handheld gamma spectrometer based on the Europium-doped Strontium Iodide scintillator, SrI2(Eu), with modern, digital readout electronics. SrI2(Eu) excels at gamma spectroscopy due to high energy resolution, high light yield (>80,000 ph/MeV), excellent light yield proportionality, and high effective atomic number (Z=49). Advances in SrI2(Eu) crystal growth have provided standardized, high quality 1.5 in. diameter crystals available for sale and for use in these handheld detectors. In these large SrI2(Eu) crystals, optical self-absorption by Eu2+ degrades the energy resolution as measured by analog electronics, but we overcome this effect through optimized crystal geometry and on the-fly correction of the scintillation pulses by digital readout electronics. Combining these two advancements, we have demonstrated performance improvements from >5.3% FWHM at 662 keV to 3.0% FWHM at 662 keV and up to 30% increase in scintillation light collection. To prepare this prototype detector for field use, we have integrated radioisotope identification software, showing excellent identification performance, we have verified detector performance does not significantly degrade over the temperature range from 25 °C to +45 °C, and we have optimized mechanical design of the detector to reduce the weight by 23%. These new developments demonstrate a stable, high performance handheld gamma spectrometer.