N4D3  Neutron Detectors: Detectors using Pulse Shape Discrimination

Thursday, Nov. 5  16:30-18:10  Golden West

Session Chair:  Erik Brubaker, Sandia National Laboratory, United States; Matthew Blackston, Oak Ridge National Laboratory, United States

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(16:30) N4D3-1, Neutron/Gamma Pulse Shape Discrimination in EJ-299 at High Flux

C. Payne1, P. J. Sellin1, M. Ellis2, K. Duroe2, A. Jones3, M. Joyce3, G. Randall4, R. Speller4

1Department of Physics, University of Surrey, Guildford, Surrey, UK
2Atomic Weapons Establishment, Reading, Berkshire, UK
3Department of Engineering, University of Lancaster, Lancaster, UK
4Department of Medical Physics and Biomedical Engineering, University College London, London, UK
The use of EJ-299 for security applications, with a focus on active interrogation environments, has been investigated; in this application a plastic scintillator capable of n/gamma discrimination is extremely attractive. Development of a system incorporating EJ-299 for this application requires consideration of the effect of a high flux, dynamic, mixed neutron/gamma field on performance. The RadICAL gamma imaging system has been developed into a static neutron/gamma imaging system which requires the use of multiple pieces of long thin plastic scintillator that can distinguish between the two radiation types. Using EJ-299 plastic scintillator, the effects of geometry on the observed quality of pulse shape discrimination (PSD) is demonstrated, through the use of a digital data acquisition system and a digital version of the charge integration PSD algorithm. Figure of merit data (FOM) shows that as the geometry moves away from a cube like structure towards flat panel shapes, PSD deteriorates. The affect of the incident flux on the observed quality of PSD for EJ-299 are investigated using an X-Ray generator. © British Crown Owned Copyright 2015/AWE

(16:50) N4D3-2, Composite Neutron Gamma Detector

A. Gueorguiev, E. van Loef, G. Markosyan, L. Soundara-Pandian, J. Glodo, J. Tower, K. Shah

Radiation Monitoring Devices Inc, Watertown, MA, USA
In recent years, a number of new inorganic scintillating materials have been discovered that have improved light yield, proportionality and energy resolution in comparison to traditional scintillators, such as NaI. Some of these materials also offer simultaneous thermal neutron and gamma ray detection. However, the higher manufacturing costs and relatively smaller detector sizes are limiting factors in their mass deployment. Recently significant progress has been achieved in the development of organic scintillators with dual neutron and gamma sensitivity. The production cost are low, but they have relatively low detection and photopeak efficiencies due to the low density and low-Z constituents. To address the above challenges, we developed a novel technology that combines the positive aspects of inorganic and organic scintillators. It is based on the suspension of an inorganic scintillator into an organic scintillation matrix. If for example Cs2LiYCl6:Ce (CLYC) scintillator is used, the composite detector can provide high gamma and photopeak efficiency, efficient thermal neutron detection and excellent neutron – gamma discrimination. As an organic matrix, a dual mode plastic scintillator can be used. It provides large gamma and fast neutron detection volume and serves as a light guide for the scintillation light generated in the CLYC material. Due to the significant difference between the light decay of the gamma and neutron events in the plastic scintillator host matrix and in the CLYC scintillator inclusions, the radiation events in both materials can be separated using pulse shape discrimination (PSD). We produced prototypes of composite detectors with up to 2” diameters and up to 4” length. The evaluation of the prototypes demonstrated that the neutron detection performance, including neutron efficiency and neutron-gamma discrimination, is not significantly affected by the size and shape of the detectors.

(17:10) N4D3-3, Ultra-High Resolution Digital Detector for Neutron Imaging with Efficient Gamma Discrimination

M. J. More1, S. Miller1, T. Hossain2, C. Fullwood2, A. Craft3, V. Nagarkar1

1Radiation Monitoring Devices, Watertown, MA, United States
2Cerium Laboratories, Austin, TX, United States
3Idaho National Laboratory, Idaho Falls, ID, United States
Neutron radiography is currently employed in non-destructive testing (NDT) as well as in many fundamental research applications. Existing neutron imaging detectors are primarily scintillator screen based, which provide excellent spatial resolution with adequate sensitivity. However, they are not suitable in applications where excessive gamma background is present, for example in imaging spent nuclear fuel. Here we report on the development of an ultra-high resolution solid-state digital imaging detector based on neutron intercepting integrated circuit that offers high sensitivity to thermal neutrons, is insensitive to gamma radiation, has fast temporal response, is able to image highly-radioactive specimens with high spatial resolution, and can withstand intense mixed radiation environments. Data acquired at the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) and at the Idaho National Laboratory (INL) has demonstrated spatial resolution on the order of 120 lp/mm (<5 µm) for thermal neutron imaging, approaching the intrinsic limits of the technology, and no sensitivity to intense gamma background. As such the detector is uniquely suited for applications in transient testing, microtomography, digital radiography, and homeland security.

(17:30) N4D3-4, A New Multi-Layer Scintillation Detectors for Detection of Neutron-Gamma Radiation

V. D. Ryzhikov1, S. V. Naydenov2, G. M. Onishchenko1, L. A. Piven1, V. S. Zvereva1, T. Pochet3, C. F. Smith4

1Institute for Scintillation Materials, Kharkov, Ukraine
2Institute for Single Crystals, Kharkov, Ukraine
3DETEC-Europe, Vannes, France
4U.S. Naval Postgraduate School, Monterey, USA
We present the results of our experimental and theoretical studies on the detection efficiency of fast neutrons from 239Pu-Be and 252Cf sources by a newly-developed type of multi-layer scintillation detector comprised of a series of alternating layers of a composite inorganic scintillator material and a plastic scintillator material. The inorganic scintillator layers consist of a composite of ZnSe(Te) and ZWO in which fast neutrons interact with the scintillator material to produce mid-energy gamma-quanta (with a working spectral range of 20-300 keV) which then produce scintillation light; and the plastic scintillator layers that serve primarily as light-guides directing the scintillation light to a photo-receiving device. Because of the relatively low transparency of the composite inorganic scintillator, better light collection conditions are ensured by incorporation of a light guide between the composite scintillator layers. We have assigned the designation ZEBRA to define this class of detectors. The sandwich structure can be comprised of any number of plates, with no limitations for thickness or area. We have also developed a promising approach to suppress external gamma radiation for new neutron-gamma detectors. It is the method of mathematical processing of the output spectrum by considering 2-3 spectral windows, and applying a newly-developed model of fast neutron analysis which is capable of deducing of the ?-spectral component from an accompanying ?-source. For the detection of fast neutrons against the background of interfering gamma-radiation (both accompanying radiation from the neutron sources and radiation from external gamma-sources), the “windows” method has a n/? sensitivity ratio reaching 104-106 in detection of weak neutron fluxes from 101 to 102 n/cm2. In summary, based on these results, we have developed several detectors of the ZEBRA type, and associated software algorithms, which enable high sensitivity detection of nuclear materials.

(17:50) N4D3-5, Gadosphere: a High-Scale Plastic Scintillator Sphere with a Gadolinium Core for Thermal Neutron Detection

J. N. Dumazert1, R. Coulon1, F. Carrel1, F. Sguerra1, E. Rohée1, S. Normand1, L. Méchin2, M. Hamel1

1DRT/LIST/DM2I/LCAE, Commissariat a l'Energie Atomique, Gif-sur-Yvette, France
2UCBN/ENSICAEN/GREYC, Centre National de la Recherche Scintifique, Caen, France
Neutron detection forms a critical branch of nuclear-related issues, currently driven by the search for alternative technologies to neutron counters based on the helium-3 isotope. The deployment of plastic scintillators shows a potential for efficient detectors, safer and more reliable than liquids, more scalable and cost-effective than inorganics. In the meantime, natural gadolinium, through its 155 and 157 isotopes, presents an exceptional interaction probability with thermal neutrons. This paper introduces a dual system including a metal gadolinium core inserted at the center of a high-scale plastic scintillator sphere. Incident fast neutrons are thermalized by the scintillator shell then captured with a significant probability by gadolinium nuclei in the core. The deposition of a sufficient fraction of the high-energy prompt gamma signature inside the scintillator shell will then allow discrimination from background radiations by energy threshold, and therefore neutron detection. The scaling of the system with the MCNPX code was carried out according to a tradeoff between the thermalization of incident fast neutrons and the probability of slow neutron capture by a moderate-cost gadolinium core. Based on the simulation, a laboratory prototype for the assessment of the detection method has been synthesized. The sensitivity and robustness of the neutron detection principle are evaluated by two counting experiments. Both simulation and experiment results confirm the potential for a highly sensitive (48 cps count rate for californium-252 of activity 1.2 MBq at a 30 cm distance), stable (variation of the count rate within Poisson uncertainty in presence of an amplitude-varying cesium-137 background), transportable (6-liter volume) and cost-efficient (a few hundreds euro) neutron detector. Further research will be carried out around the choice of an optimal matrix to maximize the extraction of scintillation photons, as well as cosmic radiation and pile-up rejection.