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Session chair: Fiederle , Michael (Albert-Ludwigs-Universität Freiburg, Freiburger Materialforschungszentrum (FMF), Freiburg, Germany); James , Ralph B. (Savannah River National Laboratory, Science & Technology Directorate, Aiken, USA)
Shortcut: R-01
Date: Monday, 18 October, 2021, 2:00 PM - 3:40 PM
Room: RTSD
Session type: RTSD Session


Click on an contribution to preview the abstract content.

2:00 PM R-01-01

RTSD Welcome and Introduction (#316)

R. B. James1, T. Takahashi2

1 Savannah River National Laboratory, Science & Technology Directorate, Aiken, South Carolina, United States of America
2 The University of Tokyo, Kavli IPMU, Chiba, Japan


On behalf of the RTSD Scientific Advisory Committee, I am pleased to welcome you to the 28th International Symposium on Room-Temperature Semiconductor Radiation Detectors.

The focus for this RTSD spans from scientific underpinnings in crystal growth to materials characterization, detector fabrication, device testing, feedback to growth and processing procedures, electronic readout development, novel instrumentation, and field uses. This vertical integration from understanding the starting materials to challenges in manufacturing instruments is very unusual, but our approach accelerates the maturity of our field. Now, you are here, and it is up to you to build on the commonality of your work, to share your data, energy, and experience with your colleagues, as we explore new ways to cooperate and collaborate in a mutually beneficial manner. By working together, we will be able to solve problems more effectively, plan better, get results more rapidly, maximize our opportunities, and achieve our vision of wide-scale deployment of room-temperature semiconductor detector technology in healthcare, security, astrophysics, environmental, mineral/oil exploration, materials sorting, among many other applications.

Before beginning our technical program, I would like to shift my comments to a few announcements about the 2021 RTSD.

Keywords: RTSD, Welcome and Introduction
2:06 PM R-01-02

Evaluation of the Spectroscopic Performance of 3D CZT drift strip detectors (#1132)

N. Auricchio1, E. Caroli1, S. Del Sordo2, L. Abbene3, J. B. Stephen1, F. Principato3, G. Gerardi3, A. Buttacavoli3, N. Protti4, M. Bettelli5, N. Sarzi Amadè5, S. Zanettini6, A. Zappettini5

1 INAF, OAS Bologna, Bologna, Italy
2 INAF, IASF Palermo, Palermo, Italy
3 University of Palermo, Department of Physics and Chemistry (DiFC), Palermo, Italy
4 University of Pavia, Department of Physics, Pavia, Italy
5 CNR, IMEM, Parma, Italy
6 due2lab s.r.l., Reggio Emilia, Italy


CdTe/CZT is an attractive and consolidated material with which to realize detectors with good efficiency and energy resolution, operating at room temperature and suitable for a large variety of applications such as medical imaging, nuclear security and astrophysics. Right in this last field several spectro-imagers based on these CdTe/CZT detectors were mounted on board space missions such as INTEGRAL, Swift, and NuSTAR for hard X and gamma ray astrophysics. Much effort has been expended in the development of CZT spectroscopic imagers for obtaining sub-millimeter spatial resolution in three dimensions (3D) and high energy resolution up to 1 MeV. The motivations are mainly related to the possibility to perform simultaneous measurements of energy, timing and 3D positioning of X and gamma rays. This kind of 3D detector is particularly suitable to realize scattering polarimeters and Advanced Compton detectors. In this paper we present the performance of high resolution CZT drift strip detectors, recently realized at IMEM-CNR (Parma, Italy) in collaboration with due2lab company (Scandiano, Italy). The detectors are operated in the Planar Transverse Field (PTF) configuration, in which photons hit the detector orthogonally to the direction of the electric field established between the two electrodes, as well as in the standard configuration. They are able to determine the 2D position thanks to the strips deposited on electrodes orthogonally, while the third coordinate is derived from the Cathode/Anode ratio and/or drift time. We report the experimental results in terms of energy resolution, peak-to valley ratio, threshold, and gain, as well as charge collection efficiency for 2 different samples and for several energies of calibration. We also report the results obtained by using a novel correction technique based on the analysis of collected-induced charge pulses from anode and drift strips.

Keywords: X-ray and Gamma-ray detectors, Spectroscopy, Semiconductor radiation detectors
2:21 PM R-01-03

Timing Resolution Measurement of CdZnTe for Time of Flight PET (#1340)

I. Blevis1, N. Wainer1, A. Altman1

1 Philips Medical Systems, Haifa, Israel


CZT has been employed commercially in medical imaging in restricted applications like bone mineral densitometry and Nuclear Medicine. Whereas CZT is being seriously considered for high volume applications like CT, it is not widely considered for PET imaging which has evolved rapidly in two decades including steady progress on Time of Flight timing resolution.  In early measurements the timing jitter for CZT detection of coincident 511 gammas was found to be 2ns rms, not competitive with the current PET standards of 200-500ns. A review of those results showed that the inaccuracies arose from dark current fluctuations and slow signal rise times, both of which are significantly different in Philips current CZT configurations. This CZT has dark current that is 1/100 and E field that is 5x those of the previous study, so there are expectations up to 50x improvement in timing resolution, 40 ps. To check this, signal current profiles for gammas from Co57 absorbed in CZT slabs were recorded and analyzed offline. The profiles have varying rising slopes depending on the Gamma energy and the E field. The timing error was determined from the measurement error for the intercept of the fitted slope and the fitted baseline. The Co57 Gammas have energies up to 706keV, comparable with PET applications. Current profiles of 100’s of  absorbed gamma were recorded to asses the jitter. Systematic error was investigated using distributions of the determined jitter over the range of Energies, interaction depths and biases. The timing jitter determined this way was close to 500ps, 4x better than the previous value and with a limiting factor thougth to be the preamplifier slew rate. These results indicate that faster values with an improved setup may be possible. These techniques are also expected to be transferrable to heavier Semiconductor radiation detectors such as the Thalium Halides and Peroskovites where the detection absorption efficiency is also much higher.

Keywords: CZT, TOF, Time of Flight, PET
2:36 PM R-01-04

Study of radiation-induced effects in 8x8x32 mm3 CdZnTe position-sensitive virtual Frisch-grid detectors in Low-Earth Orbit space instruments (#223)

A. E. Bolotnikov1, G. Carini1, A. Dellapennaa1, J. Fried1, G. Deptuch1, J. Haupt1, S. Herrmann1, I. Kotov1, A. Moiseev2, 3, G. Pinaroli1, A. Rusek1, M. Sasaki2, 3, M. Sivertz1, L. D. Smith3, E. A. Yates2

1 Brookhaven National Laboratory, Instrumentation Division, Upton, New York, United States of America
2 CRESST/NASA/GSFC, Greenbelt, Maryland, United States of America
3 University of Maryland, College Park, MD 20771, USA, College Park, Maryland, United States of America


Arrays of CdZnTe (CZT) position-sensitive virtual Frisch-grid (VFG) detectors with individual detector dimensions of 8x8x32 mm3 have been recently proposed for use in future gamma-ray space telescopes. One of the concerns of using such detectors in low Earth orbits (LEO) is the potential effects of cosmic radiation on detector performance: polarization and radiation damage caused by charged cosmic rays, mainly protons. Here, we report on the results from investigations of the detrimental effects of 100-500 MeV protons on the performance of the 32-mm long CZT detectors. The measurements were carried out at the NASA Space Radiation Laboratory (NSRL) on the BNL campus—the facilities for studying space radiation effects. We observed no polarization in such long CZT crystals even at proton fluxes several times greater than that expected in orbit. However, we did observe a reduction in the CZT electron lifetime after exposure at high proton fluences previously observed by other researchers and attributed to CZT radiation damage caused by energetic protons.

Keywords: CdZnTe detectors, crystal defects, CZTposition-sensitive Frisch-grid detectors, radiation effects
2:51 PM R-01-05

High-Resolution High-µτ Single Crystal CsPbBr3 Gamma Detectors (#379)

A. Datta1, R. Toufanian1, P. Becla1, S. Swain1, K. Becla1, S. Motakef1

1 CapeSym, Inc., R&D, Natick, Massachusetts, United States of America


Efficient gamma spectroscopy has a wide range of applications in homeland security and nuclear nonproliferation fields. CZT radiation detectors are currently the only commercially available room-temperature semiconductor detectors that are suitable for these applications. However, even with decades of research and development efforts, the production yield of these detectors is low. This results in a continued high CZT detector price which is detrimental for widespread applications. A new class of solid-state ionizing radiation detectors based on perovskite single crystals such as cesium lead bromide (CsPbBr3) is emerging as excellent spectroscopic gamma detectors and a strong competitor to CZT and TlBr, both in terms of innate properties and potentially significantly lower production cost. In addition, CsPbBr3 does not suffer from the highly deleterious effects of halide electro-migration in TlBr devices. We present results on crystal growth of CsPbBr3 using different techniques, including vertical Bridgman, Czochralski, and solution-based processes. Single crystal detector volumes as large as 250cm3 were obtained. Energy resolutions as low as 2% were obtained using CsPbBr3 detectors fabricated from these crystals for the 662keV gamma line. The detectors exhibited very high mobility-lifetime (µτ)h values of 1.7x10-2 cm2/V for hole carriers.

AcknowledgmentThis material is based upon work supported by the U.S. Department of Energy, Office of DNN R&D Award Number DE-SC0020900
Keywords: Gamma Detector, Semiconductor Detector, Perovskite, High Resolution Detector
3:06 PM R-01-06

Imaging and Spectral Performance of the High Energetic X-Ray Imaging Telescope (HREXI) System and Detector Modules (#1265)

B. Allen1, J. Grindlay1, J. Hong1, D. Violette1, S. Barthelmey2, P. Goodwin2

1 Center for Astrophysics | Harvard-Smithsonian, Cambridge, Massachusetts, United States of America
2 Goddard Spaceflight Center, Greenbelt, Maryland, United States of America


A prototype pixelated CdZnTe (CZT) detector system utilizing the NuSTAR ASIC and 3 mm thick Redlen CZT has been re-optimized for efficient integration into a wide-field coded aperture telescope for use in high-energy astrophysics, primarily over the 3 -- 200 keV energy range.  The new detector readout system, which builds on our continuing detector development program for large scalable spaceflight-qualified CZT arrays, has been completed using our new frontend detector crystal array (DCA) that supports a 2 × 2 array of 20 mm × 20 mm, 3 mm thick pixelated CZT detector with a pixel pitch of 604.8 um arranged in a 32 × 32 grid surrounded by a thin guard ring that is deposited on the outer edge of the detector anode surface.  The new readout system controls the ASICs mounted to our DCA frontend board using a CPLD and a single FPGA; where the FPGA interfaces with up to 4 CPLD/DCA pairs and provides the primary communications interface for this subsection of the complete detector plane.

A prototype FPGA module board (FMB) board utilizing this architecture has been created for the readout and testing of a single DCA as well as to precisely evaluate system power requirements prior to production of the next version which will realize the readout of a full 2 × 2 array of DCAs, or 4 × 4 individual CZT detectors (approximately 64 cm2 total detector area).  This prototype also includes a single Zynq SoC device which serves as the primary detector plane interface to ground support equipment (GSE) or spacecraft through USB, Ethernet, LVDS or a RS-422 link while also enabling the implementation of an on-board imaging capability for the detector plane for the real-time detection and localization of transient X-ray sources.

Pending successful demonstration of this architecture a larger array using multiple modules will be demonstrated in preparation for the earliest possible flight opportunity.

AcknowledgmentThis work was suppored under NASA Grant NNX17AE62G.
Keywords: Spaceflight, Imaging, CZT, Large Area, Scanning
3:21 PM R-01-07

Space charge dynamics in CdZnTeSe radiation detectors (#465)

J. Pipek1, M. Betušiak1, E. Belas1, R. Grill1, P. Praus1, A. Musiienko1, J. Pekárek1, U. N. Roy2, 3, R. B. James3

1 Charles University, Institute of Physics, MFF, Prague 2, Czech Republic
2 Brookhaven National Laboratory, New York, New York, United States of America
3 Savannah River National Laboratory, Aiken, South Carolina, United States of America


The space charge dynamics in cadmium zinc telluride selenide (CdZnTeSe) crystals were studied using a laser-induced transient current technique with pulsed and DC bias. The internal electric field profile was determined by Monte Carlo simulations of electron and hole transient currents combined with a numerical solution of the drift-diffusion equation coupled with Poisson’s equation. The formation of a positive space charge originating from the hole injection combined with a recombination level was found. The experiment was successfully fit by a simple model dominated by a single deep recombination level. Electron and hole drift mobilities of μe = 830 cm2/Vs and μh = 40 cm2/Vs, respectively, were determined. Good quality of prepared detector at pulsed bias with electron and hole mobility-lifetime products of (μτ)e = 1.9 × 10-3 cm2/V and (μτ)h = 1.4 × 10-4 cm2/V, respectively, were observed.


This work was supported by the Grant Agency of the Charles University under contract No. 1234119, by the grant and the Grant Agency of the Czech Republic under contract No. 18-12449S, and by the U.S. Department of Energy, Office of Defense Nuclear Nonproliferation Research and Development. The author UNR acknowledges partial support of LDRD funding from SRNL.

Keywords: Semiconductor detector, CdZnTeSe, Space charge, Time-of-flight technique

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