N3D3  Neutron Detectors: Fast Neutron Detection and Imaging

Wednesday, Nov. 4  16:30-18:10  Golden West

Session Chair:  Sara Pozzi, University of Michigan, United States; David Chichester, Idaho National Laboratory, United States

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(16:30) N3D3-1, Contribution of Noise and Statistical Uncertainties on PSD Performance of Fast Neutron Detection Systems Using Organic Scintillators

M. L. Iliev, K. D. Ianakiev, G. Y. Rusev, M. Jandel

Los Alamos National Laboratory, Los Alamos, NM, USA

Fast neutron detectors (except in limited time of flight applications) rely explicitly on Pulse Shape Discrimination (PSD) to separate detected neutrons from gamma background. There are numerous current and potential applications for neutron measurements in non-proliferation, safeguards, and homeland security. Practical field deployment of these materials requires them to conform to constrain such as size limitation, power consumption requirements, and portability. This requires a different approach from laboratory PSD instruments where signals are digitized at rates of 500 MHz and above with sometimes mixed results because of limitations in digitizer resolution at these speeds. Also, the massive amount of data generated, often has to be processed offline. This work presents simulation tools, analysis, and simulation results that were created for supporting a development effort for designing low power high performance hybrid (analog and digital) hardware for PSD signal processing. The goal is to use the tools and results presented here to reduce size, complexity and power consumption of our designs by analyzing the PSD signal properties and processing techniques such as analog pre-filtering, synchronization of the analog to digital convertor (ADC) with the detector pulse time of arrival, and noise analysis for optimal processing when noisy detectors are used. The general strategy for power reduction is to find ways to reduce sampling frequency and digital signal processing (DSP) load by shifting many demanding functions of the PSD processing to the analog part. Also, when using noisy photodetectors like silicon photomultipliers (SiPM) to replace bulky PMTs some important and often neglected noise issues are presented. The results show that it’s possible to achieve excellent PSD with lower sampling rate, and real time DSP

(16:50) N3D3-2, Fast Neutron Measurements with 7Li and 6Li Enriched CLYC Scintillators

A. Giaz1, F. Camera1,2, N. Blasi1, S. Brambilla1, C. Cattadori3, S. Ceruti1,2, F. Gramegna4, T. Marchi4, I. Mattei1, A. Mentana1, B. Million1, L. Pellegri1, M. Rebai3, S. Riboldi1,2, F. Salamida3, M. Tardocchi5, C. Boiano1

1INFN sezione di Milano, Milano, Italy
2Università degli studi di Milano, Milano, Italy
3INFN sezione di Milano Bicocca, Milano, Italy
4INFN Laboratori Nazionali di Legnaro, Legnaro (PD), Italy
5Istituto di Fisica del Plasma, Associazione EURATOM-ENEA-CNR, Milano, Italy

The crystal Cs2LiYCl6:Ce (CLYC) it is a promising scintillator material because of its energy resolution (about 4.5% at 662 keV) and its capability to identify gamma rays and fast/thermal neutrons. As the crystal CLYC contains 6Li and 35Cl isotopes, it is possible to detect thermal neutrons through the reaction 6Li(n, alpha)t and fast neutrons through the reactions 35Cl(n, p)35S and 35Cl(n, alpha)32P. The kinetic energy of the fast neutrons could therefore be measured with both the Time Of Flight (TOF) technique and with the energy signal. In this work, the response to fast neutrons (from 1.9 MeV up to 3.8 MeV) of two CLYC 1”x1” crystals was measured. The first CLYC scintillator, enriched with 6Li at 95% is ideal for thermal neutron measurements while the second one, enriched with 7Li is suitable for fast neutron measurements. The measurements of fast neutrons were performed at Legnaro National Laboratory (Italy) CN accelerator where proton beams (energies: 4.5 – 5 – 5.5 MeV) were accelerated on a 7LiF target, providing neutrons from 1.9 MeV up to 3.8 MeV. The two CLYC scintillators were placed at 0.7 m from the target, for the TOF measurements, and at 0° and at 90°, from the beam line, to produce neutrons with different energies, for each proton energy.

(17:10) N3D3-3, Portable, Fast-Neutron Tomography with an Isotopic Source and Organic Scintillation Detectors

M. J. Joyce, S. Agar, M. D. Aspinall, E. Colley, M. Colling, J. Dykes, P. Kardasopoulos, K. Mitton

Engineering, Lancaster University, Lancaster, United Kingdom

This paper describes the use of fast neutrons and a small number of organic liquid scintillation detectors to realize real-time, in-situ neutron tomography. The aim of the work was to determine whether neutron tomography can be achieved with an isotopic source as opposed to the usual requirement of installed facilities. A prototype system has been designed comprising 7 liquid scintillation counters, rotary table, solid-water collimator and reconstruction processing. A number of experiments have been carried out with three concrete samples to determine whether solid/hollow and cylindrical/cuboid characteristics can be discerned. The data indicate significant potential, highlighting the possibility of portable, in-situ low-dose tomography of samples without the need for a reactor, beam-line or scintillation screen.

(17:30) N3D3-4, High-Efficiency Directional Neutron Detection

R. Chandra, U. Gendotti, D. Murer, C. Sturzenegger

Arktis Radiation Detectors Ltd, Zurich, Switzerland

Novel detectors capable of detecting and discriminating thermal and fast neutrons have been used to achieve higher sensitivity in the passive detection of neutron sources. The dual-mode (fast and thermal) neutron detectors were used in conjunction with a specifically designed moderator, serving to increase efficiency as well as signal-to-noise by a) maximizing the fast neutron detection efficiency by reflecting fast neutrons incident from a source with initial trajectories not passing through a detector tube, and b) acting as a moderator to boost the efficiency of thermal neutron detection. This paper will describe the detectors and their application for passive source detection.

(17:50) N3D3-5, Event Localization in Bulk Organic Scintillators Using Direct Reconstruction

J. B. Braverman, E. Brubaker, J. Steele, M. Sweany

Radiation and Nuclear Detection Systems Department, Sandia National Laboratories, Livermore, CA, USA

Due to the radioactive signature of Special Nuclear Material, neutron detection provides an effective method to detect and locate sources of interest to nuclear security applications. Specifically, many of these applications rely on the ability to localize the neutron interactions in a large detector to within a smaller voxel inside the bulk volume. This is usually done using organic scintillators coupled with photodetectors. Typically, to achieve a finer position resolution within the scintillator, the scintillator is segmented, which results in an inefficient ratio of useable detector volume relative to the overall volume. It is more volumetrically efficient to use a bulk un-segmented scintillator coupled to an array of pixelated photodetectors. Prior work on the Single Volume Scatter Camera has shown that, with sufficiently good spatial and temporal resolution of the photodetector, finer position resolution can be achieved through a maximum likelihood estimation method. A scintillator bead within a larger inactive volume has been manufactured to provide neutron interactions at a known location within a volume. Additionally, a position sensitive microchannel plate photomultiplier tube has been partially instrumented with readout electronics. This paper reports on the findings in using the first prototype of the experimental system, and how the overall system changes when the findings are folded back into the original simulations.