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Liquid-Xe detector for contraband detection
Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Liquid-Xe detector for contraband detection D. Vartsky a,n, I. Israelashvili a,c, M. Cortesi b, L. Arazi a, A.E. Coimbra a, L. Moleri a, E. Erdal a, D. Bar a, M. Rappaport a, S. Shchemelinin a, E.N. Caspi c, O. Aviv d, A. Breskin a a
Weizmann Institute of Science, Rehovot 76100, Israel National Superconducting Cyclotron Laboratory, East Lansing 48823, MI, USA c Nuclear Research Center of Negev (NRCN), Beer-Sheva 9001, Israel d Soreq NRC, Yavne 81800, Israel b
art ic l e i nf o
Keywords: Liquid xenon SNM THGEM Gaseous Photomultiplier (GPM) NDT
a b s t r a c t We describe progress made with a liquid-Xe (LXe) detector coupled to a gaseous photomultiplier (GPM), for combined imaging and spectroscopy of fast neutrons and gamma-rays in the MeV range. The purpose of this detector is to enable the detection of hidden explosives and fissile materials in cargo and containers. The expected position resolution is about 2 m and 3.5 mm for fast neutrons and gamma-rays, respectively. Experimental results obtained using an 241Am source yielded energy and time resolutions of 11% and 1.2 ns RMS, respectively. Initial results obtained with the position-sensitive GPM are presented. & 2015 Published by Elsevier B.V.
1. Introduction
2. Simulation studies
In recent years, attempts have been made by a German-Israeli collaboration [1,2] to combine the detection of concealed explosives and Special Nuclear Materials (SNM) in a single system. The collaboration developed a Time-Resolved-EventCounting-Optical-Radiation (TRECOR) detector which uses two types of radiation detectors (plastic scintillator and LYSO crystals) viewed by a common optical system for imaging and spectroscopy of fast neutrons and gamma-rays respectively [3–5]. The inspected object is scanned sequentially with the two types of detectors. In 2012 a novel concept of a combined neutron and gamma-ray detector was proposed [6]. It uses liquid xenon (LXe) as a detection medium for simultaneous detection of both types of radiation. Fig. 1 shows a schematic drawing of the LXe detector. Neutrons/gamma-rays interact with the liquid Xe converter. The resulting scintillation photons at 178 nm enter a gaseous photomultiplier (GPM [7]) and are detected by a reflective CsI photocathode, coated on Thick Gas Electron Multiplier (THGEM [8]). The resulting photo-electrons are multiplied in subsequent THGEM stages and are detected by a position-sensitive readout electrode.
The entire detector setup was computer-simulated using the GEANT 4 code [9]. The LXe converter consisted of 50 mm thick plain-LXe medium or LXe-filled capillaries made of Teflon, polyethylene or hydrogen-containing Teflon (Tefzel). The investigated parameters were: neutron and gamma-ray spectral response, position resolution, detection efficiency, imaging capability and elemental reconstruction of an inspected object. It was shown that FWHM position resolution of 1.5–2 mm and up to 3.5 mm for fast neutrons and gamma-rays respectively is achievable., while the detection efficiency for a 50 mm thick LXe converter amounted to about 20% and 40% for fast neutrons and gamma-rays respectively.
n
Corresponding author. E-mail address: [email protected] (D. Vartsky).
3. Experimental results The response of the GPM to LXe light was measured using the Weizmann Institute Liquid Xenon (WILiX) cryostat [10]. The GPM consisted of a cascaded structure of three THGEMs, with an active diameter of 100 mm. The first THGEM is coated with a reflective 300 nm thick CsI photocathode. In this setup the signals were recorded from an un-segmented anode readout plane. The GPM was operated with Ne/CH4(5%) at 0.7 bar and 180 °K. The total gain of the GPM was about 105. Fig. 2 shows the triple-THGEM GPM assembly. The response of the GPM to LXe light was determined using an 241 Am α-source deposited on a disk and positioned within the LXe converter. Fig. 3 shows its pulse-height spectrum recorded with the GPM. Due to the geometry of the system the number of
http://dx.doi.org/10.1016/j.nima.2015.10.104 0168-9002/& 2015 Published by Elsevier B.V.
Please cite this article as: D. Vartsky, et al., Nuclear Instruments & Methods in Physics Research A (2015), http://dx.doi.org/10.1016/j. nima.2015.10.104i
D. Vartsky et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Gas photomultiplier (GPM)
LXe Converter
Fig. 1. Schematic drawing of the LXe detector. See text for details. Fig. 4. GPM timing resolution of LXe scintillation light from
241
Am α source.
4” triple-THGEM GPM
CsI coated THGEM
Fig. 2. View of a triple THGEM GPM with a CsI-coated first THGEM.
Fig. 5. Segmented 61 pixel hexagonal-pad readout. Pad side is 6 mm.
Fig. 3. Pulse height spectrum of LXe scintillation light due to 5.47 MeV α particles from an 241Am source.
created photoelectrons per event amounted to few dozens. The the RMS energy resolution was σ/E 11%. The timing properties of the GPM were determined using the 241 Am α-source. A signal from a vacuum PM which views the the LXe scintillation was used as a trigger. Fig. 4 shows the distribution of the time difference between the trigger and GPM pulses. The resulting time resolution of the GPM was 1.2 ns RMS for signals comprising of 30 photoelectrons. For details on GPM properties see [11]. Prior to its installation for imaging experiments in LXe the GPM readout system was subject to room temperature experiments with X-ray and alpha sources.The two-stage THGEM multiplier was followed by a segmented 61-pixel hexagonal pads readout
shown in Fig. 5. The detector was operated with Ne/CH4(5%) at 1 bar. The pad's side is 6 mm. This is adequate for achieving spatial resolution of 2–3 mm FWHM. The readout system was studied with 55Fe 5.9 keV X-rays yielding single-pad hits and with an 241 Am α source positioned within a few-mm thick drift gap preceding the first THGEM electrode. The α particles were emitted in a plane parallel to the THGEM electrode. Fig. 6 shows two qualitative examples of recorded α tracks. One can observe the indication of the Bragg peak at the end of the track. GPM experiments with UV-photons are in course and will be followed by LXe detector investigations with fast neutrons and gamma-rays.
Acknowledgments The authors wish to thank L. Broshi, Z. Yungrais and T. Reimer from Soreq NRC for the preparation of the 241Am sources. The work is supported in parts by the Minerva Foundation with funding from the German Ministry for Education and Research (Grant no. 710827), the Israel Science Foundation (Grant no. 477/ 10) and the PAZY Foundation (Grant no. 258/14). A. Breskin. is the W.P. Reuther Professor of Research in the Peaceful Use of Atomic Energy.
Please cite this article as: D. Vartsky, et al., Nuclear Instruments & Methods in Physics Research A (2015), http://dx.doi.org/10.1016/j. nima.2015.10.104i
D. Vartsky et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Fig. 6. Two α-tracks measured by the readout. The grey level code indicates the amount of charge collected by each pad.
References [1] M.B. Goldberg, et al., A dual purpose ion accelerator for nuclear-reaction-based explosives and SNM-detection in Massive Cargo, in: International Topical Meeting on Applications and Utilization of Accelerators, Vienna, 2008, arXiv:1001.3255. [2] B. Bromberger, et al., Monte-Carlo simulations of neutron-induced activation in fast-neutron and gamma-based cargo inspection system, JINST 7 (2012) CO3024. [3] M. Brandis, et al., Neutron measurements with time-resolved event-counting optical radiation (TRECOR) detector, JINST 7 (2012) CO4003. [4] S. Schoessler, et al., Time and position-sensitive single-photon detector for scintillation readout, JINST 7 (2012) CO2048. [5] M. Brandis, Development of Gamma-Ray Detector for Z-Selective Radiographic Imaging (Ph.D. thesis), 2013.
[6] A. Breskin, et al., A Novel liquid-Xenon Detector Concept for Combined Fastneutrons and Gamma imaging and Spectroscopy, JINST 7 (2012) CO6008. [7] R. Chechik, A. Breskin, Advances in gaseous photomultipliers, Nuclear Instruments and Methods A595 (2008) 116–127. [8] A. Breskin, et al., A concise review on THGEM detectors, Nuclear Instruments and Methods A598 (2009) 107–111. [9] I. Israelashvili, et al., A comprehensive simulation study of a liquid Xe detector for contraband detection, JINST 10 (2015) PO3030. [10] L. Arazi, et al., A. Cryogenic gaseous photomultipliers and liquid hole-multipliers: advances in THGEM-based sensors for future noble-liquid TPCs, in: Proceedings of the 7th Symposium on large TPCs for Low Energy Rare Events Detection, Paris, 2014 (to be published in the Journal of Physics:Conference Series). [11] L. Arazi, et al., First Results of a Large-area Cryogenic Gaseous Photomultiplier Coupled to a Dual-phase Liquid Xenon TPC (submitted to JINST).
Please cite this article as: D. Vartsky, et al., Nuclear Instruments & Methods in Physics Research A (2015), http://dx.doi.org/10.1016/j. nima.2015.10.104i
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Liquid-Xe detector for contraband detection D. Vartsky a,n, I. Israelashvili a,c, M. Cortesi b, L. Arazi a, A.E. Coimbra a, L. Moleri a, E. Erdal a, D. Bar a, M. Rappaport a, S. Shchemelinin a, E.N. Caspi c, O. Aviv d, A. Breskin a a
Weizmann Institute of Science, Rehovot 76100, Israel National Superconducting Cyclotron Laboratory, East Lansing 48823, MI, USA c Nuclear Research Center of Negev (NRCN), Beer-Sheva 9001, Israel d Soreq NRC, Yavne 81800, Israel b
art ic l e i nf o
Keywords: Liquid xenon SNM THGEM Gaseous Photomultiplier (GPM) NDT
a b s t r a c t We describe progress made with a liquid-Xe (LXe) detector coupled to a gaseous photomultiplier (GPM), for combined imaging and spectroscopy of fast neutrons and gamma-rays in the MeV range. The purpose of this detector is to enable the detection of hidden explosives and fissile materials in cargo and containers. The expected position resolution is about 2 m and 3.5 mm for fast neutrons and gamma-rays, respectively. Experimental results obtained using an 241Am source yielded energy and time resolutions of 11% and 1.2 ns RMS, respectively. Initial results obtained with the position-sensitive GPM are presented. & 2015 Published by Elsevier B.V.
1. Introduction
2. Simulation studies
In recent years, attempts have been made by a German-Israeli collaboration [1,2] to combine the detection of concealed explosives and Special Nuclear Materials (SNM) in a single system. The collaboration developed a Time-Resolved-EventCounting-Optical-Radiation (TRECOR) detector which uses two types of radiation detectors (plastic scintillator and LYSO crystals) viewed by a common optical system for imaging and spectroscopy of fast neutrons and gamma-rays respectively [3–5]. The inspected object is scanned sequentially with the two types of detectors. In 2012 a novel concept of a combined neutron and gamma-ray detector was proposed [6]. It uses liquid xenon (LXe) as a detection medium for simultaneous detection of both types of radiation. Fig. 1 shows a schematic drawing of the LXe detector. Neutrons/gamma-rays interact with the liquid Xe converter. The resulting scintillation photons at 178 nm enter a gaseous photomultiplier (GPM [7]) and are detected by a reflective CsI photocathode, coated on Thick Gas Electron Multiplier (THGEM [8]). The resulting photo-electrons are multiplied in subsequent THGEM stages and are detected by a position-sensitive readout electrode.
The entire detector setup was computer-simulated using the GEANT 4 code [9]. The LXe converter consisted of 50 mm thick plain-LXe medium or LXe-filled capillaries made of Teflon, polyethylene or hydrogen-containing Teflon (Tefzel). The investigated parameters were: neutron and gamma-ray spectral response, position resolution, detection efficiency, imaging capability and elemental reconstruction of an inspected object. It was shown that FWHM position resolution of 1.5–2 mm and up to 3.5 mm for fast neutrons and gamma-rays respectively is achievable., while the detection efficiency for a 50 mm thick LXe converter amounted to about 20% and 40% for fast neutrons and gamma-rays respectively.
n
Corresponding author. E-mail address: [email protected] (D. Vartsky).
3. Experimental results The response of the GPM to LXe light was measured using the Weizmann Institute Liquid Xenon (WILiX) cryostat [10]. The GPM consisted of a cascaded structure of three THGEMs, with an active diameter of 100 mm. The first THGEM is coated with a reflective 300 nm thick CsI photocathode. In this setup the signals were recorded from an un-segmented anode readout plane. The GPM was operated with Ne/CH4(5%) at 0.7 bar and 180 °K. The total gain of the GPM was about 105. Fig. 2 shows the triple-THGEM GPM assembly. The response of the GPM to LXe light was determined using an 241 Am α-source deposited on a disk and positioned within the LXe converter. Fig. 3 shows its pulse-height spectrum recorded with the GPM. Due to the geometry of the system the number of
http://dx.doi.org/10.1016/j.nima.2015.10.104 0168-9002/& 2015 Published by Elsevier B.V.
Please cite this article as: D. Vartsky, et al., Nuclear Instruments & Methods in Physics Research A (2015), http://dx.doi.org/10.1016/j. nima.2015.10.104i
D. Vartsky et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Gas photomultiplier (GPM)
LXe Converter
Fig. 1. Schematic drawing of the LXe detector. See text for details. Fig. 4. GPM timing resolution of LXe scintillation light from
241
Am α source.
4” triple-THGEM GPM
CsI coated THGEM
Fig. 2. View of a triple THGEM GPM with a CsI-coated first THGEM.
Fig. 5. Segmented 61 pixel hexagonal-pad readout. Pad side is 6 mm.
Fig. 3. Pulse height spectrum of LXe scintillation light due to 5.47 MeV α particles from an 241Am source.
created photoelectrons per event amounted to few dozens. The the RMS energy resolution was σ/E 11%. The timing properties of the GPM were determined using the 241 Am α-source. A signal from a vacuum PM which views the the LXe scintillation was used as a trigger. Fig. 4 shows the distribution of the time difference between the trigger and GPM pulses. The resulting time resolution of the GPM was 1.2 ns RMS for signals comprising of 30 photoelectrons. For details on GPM properties see [11]. Prior to its installation for imaging experiments in LXe the GPM readout system was subject to room temperature experiments with X-ray and alpha sources.The two-stage THGEM multiplier was followed by a segmented 61-pixel hexagonal pads readout
shown in Fig. 5. The detector was operated with Ne/CH4(5%) at 1 bar. The pad's side is 6 mm. This is adequate for achieving spatial resolution of 2–3 mm FWHM. The readout system was studied with 55Fe 5.9 keV X-rays yielding single-pad hits and with an 241 Am α source positioned within a few-mm thick drift gap preceding the first THGEM electrode. The α particles were emitted in a plane parallel to the THGEM electrode. Fig. 6 shows two qualitative examples of recorded α tracks. One can observe the indication of the Bragg peak at the end of the track. GPM experiments with UV-photons are in course and will be followed by LXe detector investigations with fast neutrons and gamma-rays.
Acknowledgments The authors wish to thank L. Broshi, Z. Yungrais and T. Reimer from Soreq NRC for the preparation of the 241Am sources. The work is supported in parts by the Minerva Foundation with funding from the German Ministry for Education and Research (Grant no. 710827), the Israel Science Foundation (Grant no. 477/ 10) and the PAZY Foundation (Grant no. 258/14). A. Breskin. is the W.P. Reuther Professor of Research in the Peaceful Use of Atomic Energy.
Please cite this article as: D. Vartsky, et al., Nuclear Instruments & Methods in Physics Research A (2015), http://dx.doi.org/10.1016/j. nima.2015.10.104i
D. Vartsky et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Fig. 6. Two α-tracks measured by the readout. The grey level code indicates the amount of charge collected by each pad.
References [1] M.B. Goldberg, et al., A dual purpose ion accelerator for nuclear-reaction-based explosives and SNM-detection in Massive Cargo, in: International Topical Meeting on Applications and Utilization of Accelerators, Vienna, 2008, arXiv:1001.3255. [2] B. Bromberger, et al., Monte-Carlo simulations of neutron-induced activation in fast-neutron and gamma-based cargo inspection system, JINST 7 (2012) CO3024. [3] M. Brandis, et al., Neutron measurements with time-resolved event-counting optical radiation (TRECOR) detector, JINST 7 (2012) CO4003. [4] S. Schoessler, et al., Time and position-sensitive single-photon detector for scintillation readout, JINST 7 (2012) CO2048. [5] M. Brandis, Development of Gamma-Ray Detector for Z-Selective Radiographic Imaging (Ph.D. thesis), 2013.
[6] A. Breskin, et al., A Novel liquid-Xenon Detector Concept for Combined Fastneutrons and Gamma imaging and Spectroscopy, JINST 7 (2012) CO6008. [7] R. Chechik, A. Breskin, Advances in gaseous photomultipliers, Nuclear Instruments and Methods A595 (2008) 116–127. [8] A. Breskin, et al., A concise review on THGEM detectors, Nuclear Instruments and Methods A598 (2009) 107–111. [9] I. Israelashvili, et al., A comprehensive simulation study of a liquid Xe detector for contraband detection, JINST 10 (2015) PO3030. [10] L. Arazi, et al., A. Cryogenic gaseous photomultipliers and liquid hole-multipliers: advances in THGEM-based sensors for future noble-liquid TPCs, in: Proceedings of the 7th Symposium on large TPCs for Low Energy Rare Events Detection, Paris, 2014 (to be published in the Journal of Physics:Conference Series). [11] L. Arazi, et al., First Results of a Large-area Cryogenic Gaseous Photomultiplier Coupled to a Dual-phase Liquid Xenon TPC (submitted to JINST).
Please cite this article as: D. Vartsky, et al., Nuclear Instruments & Methods in Physics Research A (2015), http://dx.doi.org/10.1016/j. nima.2015.10.104i