In this work we present a novel method for improving the high-temperature performance of silicon photomultipliers (SiPMs) via focused ion beam (FIB) modification of individual microcells. The literature suggests that most of the dark count rate (DCR) in a SiPM is contributed by a small percentage (<5%) of microcells. By using a FIB to electrically deactivate this relatively small number of microcells, we believe we can greatly reduce the overall DCR of the SiPM at the expense of a small reduction in overall photodetection efficiency, thereby improving its high temperature performance. In this report we describe our methods for characterizing the SiPM to determine which individual microcells contribute the most to the DCR, preparing the SiPM for FIB, and modifying the SiPM using the FIB to deactivate the identified microcells.
We report the system response of a pixelated associated particle imaging (API) neutron radiography system. The detector readout currently consists of a 2x2 array of organic glass scintillator detectors, each with an 8x8 array of optically isolated pixels that match the size and pitch of the ARRAYJ-60035-64P-PCB Silicon Photomultiplier (SiPM) array from SensL/onsemi with 6x6 mm2 SiPMs. The alpha screen of the API deuterium-tritium neutron generator is read out with the S13361-3050AE-08 from Hamamatsu, which is an 8x8 array of 3x3 mm2 SiPMs. Data from the 320 channel system is acquired with the TOFPET2-based readout system. We present the predicted imaging capability of an eventual 5x5 detector array, the waveform-based energy and pulse shape characterization of the individual detectors, and the timing and energy response from the TOFPET2 system.
The Optically Segmented Single Volume Scatter Camera (OS-SVSC) aims to image neutron sources for non-proliferation applications using the kinematic reconstruction of elastic double-scatter events. Our prototype system consists of 64 EJ-204 organic plastic scintillator bars, each measuring 5 mm × 5 mm × 200 mm and individually wrapped in Teflon tape. The scintillator array is optically coupled to two silicon photomultiplier ArrayJ-60035 64P-PCB arrays, each comprised of 64 individual 6 mm × 6 mm J-Series sensors arranged in an 8 × 8 array. We report on the design details, including component selections, mechanical design and assembly, and the electronics system. The described design leveraged existing off-the-shelf solutions to support the rapid development of a phase 1 prototype. Several valuable lessons were learned from component and system testing, including those related to the detector’s mechanical structure and electrical crosstalk that we conclude originates in the commercial photodetector arrays and the associated custom breakout cards. We detail our calibration efforts, beginning with calibrations for the electronics, based on the IRS3D application-specific integrated circuits, and their associated timing resolutions, ranging from 30 ps to 90 ps. With electronics calibrations applied, energy and position calibrations were performed for a set of edge bars using 22Na and 90Sr, respectively, reporting an average resolution of (12.07 ± 0.03) mm for energy depositions between 900 keVee and 1000 keVee. We further demonstrate a position calibration method for the internal bars of the matrix using cosmic-ray muons as an alternative to emission sources that cannot easily access these bars, with an average measured resolution of (14.86 ± 0.29) mm for depositions between 900 keVee and 1000 keVee. The coincident time resolution reported between pairs of bars measured up to 400 ps from muon acquisitions. Energy and position calibration values measured with muons are consistent with those obtained using particle emission sources.
Tellez-Galindo, A.; Brown, J.A.; Brubaker, Erik B.; Cabrera-Palmer, Belkis C.; Carlson, Joseph S.; Dorrill, R.; Druetzler, A.; Elam, J.; Febbraro, M.; Feng, P.; Folsom, M.; Galino-Tellez, A.; Goldblum, B.L.; Hausladen, P.; Kaneshige, N.; Keefe, K.; Laplace, T.A.; Learned, J.G.; Mane, A.; Manfredi, J.J.; Marleau, Peter M.; Mattingly, J.; Mishra, M.; Moustafa, A.; Nattress, J.; Nishimura, K.; Steele, J.; Sweany, Melinda; Weinfurther, K.; Ziock, K.
The Single-Volume Scatter Camera (SVSC) approach to kinematic neutron imaging, in which an incident neutron’s direction is reconstructed via multiple neutron-proton scattering events, potentially offers much greater efficiency and portability than current systems. In our first design of an Optically-Segmented (OS) SVSC, the detector consists of an 8×8 array of 5×5×200 mm3 bars of EJ-204 scintillator wrapped in Teflon tape, optically coupled with SensL J-series 6 x 6 mm Silicon Photomultiplier (SiPM) arrays, all inside an aluminum frame that serves as a dark box. The SiPMs are read out using custom (multi-GSPS) waveform sampling electronics. In this work, construction, characterization, and electronics updates are reported. The position, time, and energy resolutions of individual bars were obtained by measuring different scintillators with different reflectors. This work was carried out in parallel at the University of Hawaii and at Sandia National Laboratories and resulted in the preliminary design of the camera. Monte-Carlo simulations using the Geant4 toolkit were carried out for individual scintillator bars, as well as the array setup. A custom analysis using ROOT libraries in C++ simulated the SiPM response from Geant4 photon hits. This analysis framework is under development and will allow for seamless comparisons between experimental and simulated data.
We report on the energy, timing, and pulse-shape discrimination performance of cylindrical 5.08 cm diameter × 5.08 cm thick and 7.62 cm diameter × 7.62 cm thick trans-stilbene crystals read out with the passively summed output of three different commercial silicon photo-multiplier arrays. Our results indicate that using the summed output of an 8 × 8 array of SiPMs provides performance competitive with photo-multiplier tubes for many neutron imaging and correlated particle measurements. For a 5.08 cm diameter × 5.08 cm thick crystal read out with SensL's ArrayJ-60035_64P-PCB, which had the best overall properties, we measure the energy resolution as 17.8 ± 0.8% at 341 keVee (σ/E), the timing resolution in the 180–400 keVee range as 236 ± 61 ps (σ), and the pulse-shape discrimination figure-of-merit as 2.21 ± 0.03 in the 230–260 keVee energy range. For a 7.62 cm diameter × 7.62 cm thick crystal read out with SensL's ArrayJ-60035_64P-PCB, we measure the energy resolution as 21.9 ± 2.3% at 341 keVee, the timing resolution in the 180–400 keVee range as 518 ± 42 ps, and the pulse-shape discrimination figure-of-merit as 1.49 ± 0.01 in the 230–260 keVee energy range. These results enable many scintillator-based instruments to enjoy the size, robustness, and power benefits of silicon photo-multiplier arrays as replacement for the photo-multiplier tubes that are predominantly used today.
An optically-segmented single-volume scatter camera is being developed to image MeV-energy neutron sources. The design employs long, thin, optically isolated organic scintillator pillars with 5 mm × 5 mm × 200 mm dimensions (i.e., an aspect-ratio of 1:1:40). Teflon reflector is used to achieve optical isolation and improve light collection. The effect of Teflon on the ability to resolve the radiation interaction locations along such high aspect-ratio pillars is investigated. It was found that reconstruction based on the amplitude of signals collected on both ends of a bare pillar is less precise than reconstruction based on their arrival times. However, this observation is reversed after wrapping in Teflon, such that there is little to no improvement in reconstruction resolution calculated by combining both methods. It may be possible to use another means of optical isolation that does not require wrapping each individual pillar of the camera.
The multi-institution Single-Volume Scatter Camera (SVSC) collaboration led by Sandia National Laboratories (SNL) is developing a compact, high-efficiency double-scatter neutron imaging system. Kinematic emission imaging of fission-energy neutrons can be used to detect, locate, and spatially characterize special nuclear material. Neutron-scatter cameras, analogous to Compton imagers for gamma ray detection, have a wide field of view, good event-by-event angular resolution, and spectral sensitivity. Existing systems, however, suffer from large size and/or poor efficiency. We are developing high-efficiency scatter cameras with small form factors by detecting both neutron scatters in a compact active volume. This effort requires development and characterization of individual system components, namely fast organic scintillators, photodetectors, electronics, and reconstruction algorithms. In this presentation, we will focus on characterization measurements of several SVSC candidate scintillators. The SVSC collaboration is investigating two system concepts: the monolithic design in which isotropically emitted photons are detected on the sides of the volume, and the optically segmented design in which scintillation light is channeled along scintillator bars to segmented photodetector readout. For each of these approaches, we will describe the construction and performance of prototype systems. We will conclude by summarizing lessons learned, comparing and contrasting the two system designs, and outlining plans for the next iteration of prototype design and construction.
Brown, J.AB.; Brubaker, Erik B.; Dorril, R D.; Druetzler, A D.; Elam, J E.; Febbraro, M F.; Feng, Patrick L.; Folsom, Michael W.; Galino-Tellez, A G.; Goldblum, B.LG.; Hausladen, P H.; Kaneshige, N K.; Keffe, K K.; Laplace, T, A.; Learned, J.G.L.; Mane, A M.; Manfredi, J M.; Marleau, Peter M.; Mattingly, J M.; Mishra, Mishra; Almanza-Madrid, Rene A.; Moustafa, A M.; Nattress, J N.; Steele, John T.; Sweany, Melinda; Weinfurther, K W.; Ziock, K.Z.
We present the detector response comparison between a 10x10 pixellated array of scintillator read out with Anger logic using four 2" Hamamatsu R7724-100 super bialkali photomulti- plier tubes (PMT) and a custom Silicon photomultiplier (SiPM) board consisting of 100 C-series 6x6 mm SiPMs from SensL. An array of these pixellated detectors are currently used in the Neutron Coded Aperture (NCA) imaging system. The energy, timing and pulse shape discrimination response using both readout schemes are presented, along with an anal- ysis of multiple scatter events occurring within the block. An evaluation of the impact of photodetector readout on the overall detection efficiency and imaging accuracy is presented.
We report on the position, timing, and energy resolution of a range of plastic scintillator bars and reflector treatments using dual-ended silicon photomultiplier readout. These measurements are motivated by the upcoming construction of an optically segmented single-volume neutron scatter camera, in which neutron elastic scattering off of hydrogen is used to kinematically reconstruct the location and energy of a neutron-emitting source. For this application, interaction position resolutions of about 10 mm and timing resolutions of about 1 ns are necessary to achieve the desired efficiency for fission-energy neutrons. The results presented here indicate that this is achievable with an array of 5×5×190mm 3 bars of EJ-204 scintillator wrapped in Teflon tape, read out with SensL's J-series 6×6mm 2 silicon photomultipliers. With two independent setups, we also explore the systematic variability of the position resolution, and show that, in general, using the difference in the pulse arrival time at the two ends is less susceptible to systematic variation than using the log ratio of the charge amplitude of the two ends. Finally, we measure a bias in the absolute time of interactions as a function of position along the bar: the measured interaction time for events at the center of the bar is ∼100 ps later than interactions near the SiPM.
Dorrill, Ryan D.; Druetzler, Andrew D.; Kaneshige, Nate K.; Learned, John L.; Whitworth, A W.; Galindo-Tellez, Aline G.; Keffe, Kevin K.; Shoen, D S.; Diamond, D.D.; Tom, R T.; Sweany, Melinda; Brubaker, Erik B.