Anticoincidence Shield Research Articles

Capability demonstration of a 3D CdZnTe detector on a high-altitude balloon flight

In collaboration between the University of Michigan and Los Alamos National Laboratory, a 3D position-sensing CdZnTe (CZT) detector prototype was built and integrated into a high-altitude balloon platform to evaluate its performance in a space-like mixed-radiation environment. The detector prototype, Orion Eagle, was designed to operate in near-vacuum environments without any temperature regulation. Orion Eagle was hand-launched from NASA’s Columbia Scientific Balloon Facility (CSBF) at Fort Sumner, NM on September 26, 2021, and successfully operated throughout a 9-hour flight, which reached 38.5 km in altitude. The flight met its objectives, successfully detecting atmospheric gamma rays and galactic cosmic rays, and raising the Technical Readiness Level from 4 to 6 for large-volume 3D CZT detector technology for space applications. Ionization tracks produced by charged particles create spatial signatures in the detector that are distinguishable from discrete gamma-ray interactions. Therefore, the 3D position-sensing capabilities using pixelated electrodes on a CZT detector can help enable discrimination of background charged particles from gamma-ray events without an anticoincidence shield. The potential for background rejection capability, ambient-temperature operation, gamma-ray coded-aperture and Compton imaging, and near High Purity Germanium (HPGe) energy resolution motivate the use of large-volume 3D CZT imaging spectrometers in future space missions.

The design and performance of the XL-Calibur anticoincidence shield

The XL-Calibur balloon-borne hard X-ray polarimetry mission comprises a Compton-scattering polarimeter placed at the focal point of an X-ray mirror. The polarimeter is housed within a BGO anticoincidence shield, which is needed to mitigate the considerable background radiation present at the observation altitude of ∼40 km. This paper details the design, construction and testing of the anticoincidence shield, as well as the performance measured during the week-long maiden flight from Esrange Space Centre to the Canadian Northwest Territories in July 2022. The in-flight performance of the shield followed design expectations, with a veto threshold <100 keV and a measured background rate of ∼0.5 Hz (20–40 keV). This is compatible with the scientific goals of the mission, where %-level minimum detectable polarisation is sought for a Hz-level source rate.

Radioactivity measurement of 85Kr by using anti-cosmic HPGe γ spectrometer

In order to improve the detection sensitivity of 85Kr, an anti-cosmic HPGe γ spectrometer was established and a specific Marinelli beaker was designed for 85Kr measurement. Comparing to the non-anticoincidence γ spectrum, the integral background counts rate range from 20 to 2400 keV was reduced by a factor of 5.17 using anticoincidence shielding. The minimum detectable activity of 85Kr was 10.5 Bq within 24 h measurement in standard mode and that of 3.99 Bq in anticoincidence mode. The activity concentration of atmospheric 85Kr was preliminarily measured to be an average of 1.30 Bq/m3 in Beijing and corresponding minimum detectable concentration was 0.2 Bq/m3.

Main results of the DAMPE space detector after 4 years in orbit

The DArk Matter Particle Explorer (DAMPE) is a high-performance space particle detector launched in orbit in 2015 by a collaboration of Chinese, Italian and Swiss scientific institutions, coordinated by the Chinese Academy of Sciences. It consists of a high-resolution segmented BGO electromagnetic calorimeter with a depth of 32 radiation lengths, a silicon-tungsten tracker-converter with an angular resolution below [Formula: see text], an anti-coincidence shield and ion detector, and a neutron detector. The detector characteristics and performance, and the latest observations of cosmic electrons up to 5 TeV, protons and nuclei up to 100 TeV and gamma-rays up to 10 TeV are presented.

XL-Calibur – a second-generation balloon-borne hard X-ray polarimetry mission

XL-Calibur is a hard X-ray (15-80 keV) polarimetry mission operating from a stabilised balloon-borne platform in the stratosphere. It builds on heritage from the X-Calibur mission, which observed the accreting neutron star GX 301 - 2 from Antarctica, between December 29th 2018 and January 1st 2019. The XL-Calibur design incorporates an X-ray mirror, which focusses X-rays onto a polarimeter comprising a beryllium rod surrounded by Cadmium Zinc Telluride (CZT) detectors. The polarimeter is housed in an anticoincidence shield to mitigate background from particles present in the stratosphere. The mirror and polarimeter-shield assembly are mounted at opposite ends of a 12 m long lightweight truss, which is pointed with arcsecond precision by WASP – the Wallops Arc Second Pointer. The XL-Calibur mission will achieve a substantially improved sensitivity over X-Calibur by using a larger effective area X-ray mirror, reducing background through thinner CZT detectors, and improved anticoincidence shielding. When observing a 1 Crab source for tdaydays, the Minimum Detectable Polarisation (at 99% confidence level) is ∼2%·tday−1/2. The energy resolution at 40 keV is ∼5.9 keV. The aim of this paper is to describe the design and performance of the XL-Caliburmission, as well as the foreseen science programme.

Observation of the Second LIGO/Virgo Event Connected with a Binary Neutron Star Merger S190425z in the Gamma-Ray Range

Observations of the gravitational-wave (GW) event S190425z registered by the LIGO/Virgo detectors with the Anti-Coincidence Shield (ACS) of the gamma-ray spectrometer SPI aboard the INTEGRAL observatory are presented. With a high probability (>99%) it was associated with a neutron star (NS) merger in a close binary system. This is only the second event of such type in the history of GW observations (after GW170817). A weak gamma-ray burst, GRB190425, consisting of two pulses in ~0.5 and ~5.9 s after the NS merging in S190425z was detected by SPI-ACS. The pulses had a priori reliability of 3.5 and 4.4 sigma as single events and 5.5 sigma as a combined event. Analysis of the SPI-ACS count rate history recorded these days (~125 ks in total) has shown that the rate of appearance of two close pulses with characteristics of GRB190425 by chance does not exceed 6.4 x 10^{-5} s^{-1}. We note that the time profile of GRB190425 has a lot in common with the profile of the GRB170817A burst accompanying the GW170817 event; that both the NS mergers were the closest (<150 Mpc) of all the events registered by the LIGO/Virgo detectors; and that there were no confident excesses of gamma-ray emission over the background detected in any of >30 black hole merger events recorded to the moment by these detectors. No hard X-ray flares were detected in the field of view of the SPI and IBIS-ISGRI gamma-ray telescopes aboard INTEGRAL. This, as well as the lack of detection of gamma-ray emission from GRB190425 by the GBM monitor of the Fermi observatory assuming its occultation by the Earth, can significantly reduce the localization area for the source of this GW event. The estimates of the parameters E_{iso} and E_{p} for GRB190425 are obtained and compared with the similar parameters for GRB170817A.

The DAMPE experiment and its latest results

The DArk Matter Particle Explorer (DAMPE) is a high-performance space particle detector launched in orbit on 17 December 2015 by a collaboration of Chinese, Italian and Swiss scientific institutions, coordinated by the Chinese Academy of Sciences. It consists of a high-resolution segmented BGO electromagnetic calorimeter with a depth of 32 radiation lengths, a silicon-tungsten tracker-converter that reaches an angular resolution below 0.2°, an anti-coincidence shield and ion detector made of segmented plastic scintillators and a neutron detector made of boron-doped plastic scintillators. An overview of the experiment and a summary of the latest results coming from the observation of cosmic rays up to 100 TeV, of gamma-rays up to 10 TeV and of cosmic electrons up to 5 TeV is presented.

New Gamma-Ray Bursts Found in the Archival Data from the IBIS/ISGRI Telescope of the INTEGRAL Observatory

A systematic search for cosmic gamma-ray bursts (GRBs) and other short hard X-ray events in the archival data from the IBIS/ISGRI telescope of the INTEGRAL observatory over 2003-2018 has been carried out. Seven previously unknown GRBs have been recorded in the telescope field of view; all of them have been localized with an accuracy < 2 arcmin. These events were not revealed by the INTEGRAL burst alert system (IBAS) designed for an automatic GRB search and alert. Four more such localized events missed by IBAS, but known previously, i.e., observed in other experiments, have been found. Eight hundred and eighty six GRBs outside the field of view that arrived at large angles to the IBIS/ISGRI axis have also been recorded. All of them were previously recorded in other experiments, primarily by the anticoincidence shield (ACS) of the SPI gamma-ray spectrometer onboard INTEGRAL, the PICsIT detector of the IBIS gamma-ray telescope, and the KONUS/WIND monitor. An order of magnitude more events without any confirmations in other experiments have been recorded. Both GRBs and solar flares or magnetospheric transient events can be among them. Catalogs with the basic parameters of confirmed and previously unknown GRBs recorded by IBIS/ISGRI have been compiled. The statistical distributions of bursts in various parameters have been constructed and investigated.

Testing merging of dark exotic stars from gravitational waves in the multi-messenger approach

We discuss possible implications of the recent detection by the LIGO and VIRGO collaboration of the gravitational-wave event GW170817, the signal of which is consistent with predictions in general relativity on the merging of neutron stars. A near-simultaneous and spatially correlated observation of a gamma-ray burst, the GRB 170817A signal, was achieved independently by the Fermi Gamma-ray Burst Monitor, and by the Anti-coincidence Shield for the Spectrometer of the International Gamma-Ray Astrophysics Laboratory. Motivated by this near temporal and spatial concomitance of events, which can occur by chance only with the probability [Formula: see text], we speculate on the possibility that new dark stars signals could be detected from the LIGO/VIRGO detectors. This proposal, which aims at providing a test for some models of dark matter, relies on the recent achievement of detecting, for visible ordinary matter, the merging of neutron stars both in the gravitational and the electromagnetic channel. A lack of correlation between the two expected signals would suggest a deviation from the properties of ordinary matter. Specifically, we focus on models of invisible dark matter, and in particular we study the case of mirror dark matter, within the framework of which a large amount of mirror neutron stars are naturally envisaged to occupy our dark matter halo. The observation of an electromagnetically hidden event inside the dark matter halo of our galaxy should provide a hint of new physics. There would be indeed no satisfactorily complete explanation accounting for the lack of electromagnetic signal, if only standard neutron star merging were considered to describe events that happen so close to us.

Gamma-ray observations of Nova Sgr 2015 No. 2 with INTEGRAL

Context. INTEGRAL observed Nova Sgr 2015 No. 2 (V5668 Sgr) around the time of its optical emission maximum on 21 March 2015. Studies at UV wavelengths showed spectral lines of freshly produced 7Be. This could also be measurable in gamma rays at 478 keV from the decay to 7Li. Novae are also expected to synthesise 22Na which decays to 22Ne, emitting a 1275 keV photon. About one week before the optical maximum, a strong gamma-ray flash on timescales of hours is expected from short-lived radioactive nuclei such as 13N and 18F. These nuclei are β+-unstable, and should yield emission of up to 511 keV, but this emission has never been observed from any nova. Aims. The SPectrometer on INTEGRAL (SPI) pointed towards V5668 Sgr by chance. We use these observations to search for possible gamma-ray emission of decaying 7Be, and to directly measure the synthesised mass during explosive burning. We also aim to constrain possible burst-like emission days to weeks before the optical maximum using the SPI anticoincidence shield (ACS), i.e. at times when SPI was not pointing to the source. Methods. We extracted spectral and temporal information to determine the fluxes of gamma-ray lines at 478 keV, 511 keV, and 1275 keV. Using distance and radioactive decay, a measured flux converts into the 7Be amount produced in the nova. The SPI-ACS rates are analysed for burst-like emission using a nova model light curve. For the obtained nova flash candidate events, we discuss possible origins using directional, spectral, and temporal information. Results. No significant excess for the 478 keV, the 511 keV, or the 1275 keV lines is found. Our upper limits (3σ) on the synthesised 7Be and 22Na mass depend on the uncertainties of the distance to V5668 Sgr: the 7Be mass is constrained to less than 4.8 × 10−9 (dkpc−1)2 M⊙, and the 22Na mass to less than 2.4 × 10−8 (dkpc−1)2 M⊙. For the 7Be mass estimate from UV studies, the distance to V5668 Sgr must be greater than 1.2 kpc (3σ). During the three weeks before the optical maximum, we find 23 burst-like events in the ACS rate, of which 6 could possibly be associated with V5668.

Statistical Study of Mercury's Energetic Electron Events as Observed by the Gamma-Ray and Neutron Spectrometer Instrument Onboard MESSENGER.

We present results from a statistical analysis of Mercury's energetic electron (EE) events as observed by the gamma‐ray and neutron spectrometer instrument onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. The main objective of this study is to investigate possible anisotropic behavior of EE events using multiple data sets from MESSENGER instruments. We study the data from the neutron spectrometer (NS) and the gamma‐ray spectrometer anticoincidence shield (ACS) because they use the same type of borated plastic scintillator and, hence, they have very similar response functions, and their large surface areas make them more sensitive to low‐intensity EE events than MESSENGER's particle instrumentation. The combined analysis of NS and ACS data reveals two different classes of energetic electrons: “Standard” events and “ACS‐enhanced” events. Standard events, which comprise over 90% of all events, have signal sizes that are the same in both the ACS and NS. They are likely gyrating particles about Mercury's magnetic field following a 90° pitch angle distribution and are located in well‐defined latitude and altitude regions within Mercury's magnetosphere. ACS‐enhanced events, which comprise less than 10% of all events, have signal sizes in the ACS that are 10 to 100 times larger than those observed by the NS. They follow a beam‐like distribution and are observed both inside and outside Mercury's magnetosphere with a wider range of latitudes and altitudes than Standard events. The difference between the Standard and ACS‐enhanced event characteristics suggests distinct underyling acceleration mechanisms.

Brane-world extra dimensions in light of GW170817

The search for extra dimensions is a challenging endeavor to probe physics beyond the Standard Model. The joint detection of gravitational waves (GW) and electromagnetic (EM) signals from the merging of a binary system of compact objects like neutron stars (NS), can help constrain the geometry of extra dimensions beyond our 3+1 spacetime ones. A theoretically well-motivated possibility is that our observable Universe is a 3+1-dimensional hypersurface, or brane, embedded in a higher 4+1-dimensional Anti-de Sitter (AdS$_5$) spacetime, in which gravity is the only force which propagates through the infinite bulk space, while other forces are confined to the brane. In these types of brane-world models, GW and EM signals between two points on the brane would, in general, travel different paths. This would result in a time-lag between the detection of GW and EM signals emitted simultaneously from the same source. We consider the recent near-simultaneous detection of the GW event GW170817 from the LIGO/Virgo collaboration, and its EM counterpart, the short gamma-ray burst GRB170817A detected by the Fermi Gamma-ray Burst Monitor and the INTEGRAL Anti-Coincidence Shield spectrometer. Assuming the standard $\Lambda$-Cold Dark Matter ($\Lambda$CDM) scenario and performing a likelihood analysis which takes into account astrophysical uncertainties associated to the measured time-lag, we set an upper limit of $\ell \lesssim 0.535\,$Mpc at $68\%$ confidence level on the AdS$_5$ radius of curvature $\ell$. Although the bound is not competitive with current Solar System constraints, it is the first time that data from a multi-messenger GW-EM measurement is used to constrain extra-dimensional models. Thus, our work provides a proof-of-principle for the possibility of using multi-messenger astronomy for probing the geometry of our space-time.

Optimization of the design of X-Calibur for a long-duration balloon flight and results from a one-day test flight

X-ray polarimetry promises exciting insights into the physics of compact astrophysical objects by providing two observables: the polarization fraction and angle as function of energy. X-Calibur is a balloon-borne hard x-ray scattering polarimeter for the 15- to 60-keV energy range. After the successful test flight in September 2016, the instrument is now being prepared for a long-duration balloon (LDB) flight in December 2018 through January 2019. During the LDB flight, X-Calibur will make detailed measurements of the polarization of Vela X-1 and constrain the polarization of a sample of between 4 and 9 additional sources. We describe the upgraded polarimeter design, including the use of a beryllium scattering element, lower-noise front-end electronics, and an improved fully active CsI(Na) anticoincidence shield, which will significantly increase the instrument sensitivity. We present estimates of the improved polarimeter performance based on simulations and laboratory measurements. We present some of the results from the 2016 flight and show that we solved several problems, which led to a reduced sensitivity during the 2016 flight. We end with a description of the planned Vela X-1 observations, including a Swift/BAT-guided observation strategy.

CeBr3 scintillators for 4He prompt gamma spectroscopy: Results from a Monte Carlo optimization study

Range uncertainties limit the potential of charged particle therapy. In vivo and online range verification techniques could increase the confidence in the dose delivery distribution and lead to more conformal treatments. Prompt gamma imaging and prompt gamma spectroscopy (PGS) have been demonstrated for such a purpose. The successful application of these techniques requires the development of a dedicated detector system optimized to the radiation energy ranges and the intensity. In this work, we investigated a detector system based on CeBr3 crystals capable of performing spectroscopy of the prompt gamma radiation induced by 4 He beams. We performed Monte Carlo simulations to optimize the detector system. The study was carried out both with the Geant4 toolkit and the FLUKA package. The simulated system consisted of a primary crystal for spectroscopy and secondary crystals for noise reduction in anticoincidence (AC). For comparison purposes, we considered a configuration without AC crystals. We first defined the dimensions of the primary cerium bromide (CeBr3 ) crystal and the secondary bismuth germanate (BGO) or CeBr3 crystals. We then evaluated their detection performance for monoenergetic gamma radiation up to 7MeV in such way that the probability of the photo-peak detection was maximized in comparison to the number of escape peak and Compton events. We simulated realistic prompt gamma radiation spectra induced by 4 He beams on homogeneous targets (water, graphite, and aluminum) and on implants (water with an aluminum insert). Finally, we tested the performances of the optimized systems in the detection of the realistic gamma spectra. The quantitative analysis was accomplished by comparing the signal-to-noise ratio between the different configurations and the ability to resolve the discrete reactions. We present the optimized dimensions for the primary CeBr3 crystals with and without AC shielding. The specific values are given over a wide range of crystal volumes. The results show an optimal primary CeBr3 crystal with an approximately diameter to length ratio of 1 without AC shielding and 0.5 with AC shielding. The secondary BGO and CeBr3 should have a transverse dimension of 3 and 4.56cm, respectively. The analysis of the prompt gamma spectra from 4 He beams highlighted the presence of specific discrete reactions not observed in 1 H studies, for example, 12 C transition 0+ (7.65MeV) →2+ (4.44MeV). This reaction is responsible for the generation of the 3.21MeV prompt gamma peak. The optimized primary crystal provides a significant increase in the signal-to-noise ratio together with an improved resolution of the discrete gamma lines, especially in the high-energy region. The detection configuration with an optimized anticoincidence crystal improved the signal-to-noise ratio up to a factor of 3.5. This work provides the optimal geometry for primary and secondary crystals to be used in range verification through PGS. The simulations show that such a PGS system may allow for the simultaneous detection of the discrete lines from a thin metal implant within a water phantom.

The DAMPE experiment: 2 year in orbit

The DArk Matter Particle Explorer (DAMPE) is a space mission within the strategic framework of the Chinese Academy of Sciences, resulting from a collaboration of Chinese, Italian, and Swiss institutions, and is a new addition to the growing number of particle detectors in space. It was successfully launched in December 2015 and has commenced nominal science operations since shortly after launch. Lending technologies from its predecessors such as AMS and Fermi-LAT, it features a powerful segmented electromagnetic calorimeter which thanks to its 31 radiation lengths enables the study of charged cosmic rays in the energy domain of up to 100 TeV and gamma rays of up to 10 TeV. The calorimeter is complemented with a silicon-tungsten tracker converter which yields a comparable angular resolution as current space-borne pair-conversion gamma-ray detectors. In addition, the detector features a top anti-coincidence shield made of segmented silicon plastic scintillators and a boron-doped plastic scintillator on the bottom of the instrument to detect delayed neutrons arising from cosmic ray protons showering in the calorimeter. An overview of the mission and a summary of the latest results in the domain of charged cosmic rays, gamma rays and heavy ions will be presented.

Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory

The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anticoincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the GeV--EeV energy range using the ANTARES, IceCube, and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within $\pm500$ s around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We further carried out an extended search in the direction of the source for high-energy neutrinos within the 14-day period following the merger, but found no evidence of emission. We used these results to probe dissipation mechanisms in relativistic outflows driven by the binary neutron star merger. The non-detection is consistent with model predictions of short GRBs observed at a large off-axis angle.

Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A

Abstract On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is 5.0 × 10 − 8 . We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of ( + 1.74 ± 0.05 ) s between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between − 3 × 10 − 15 and + 7 × 10 − 16 times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1–1.4 per year during the 2018–2019 observing run and 0.3–1.7 per year at design sensitivity.

Response function simulation of the anti-coincidence detector based on NaI crystal with a complex shape in registration systems for the experiments SAGE and BEST

Response function simulation using Geant 4 for the detector based on NaI crystal of complex shape in registration systems for the SAGE and BEST experiments is presented. Cylindric NaI crystal has a large well for placing up to eight proportional counters. The detector is using as anti-coincidence shield for counters and an instrument for analysis of different γ-rays sources. The result of detector response function simulation for different background sources and their registration efficiency are given.

Low-level gamma-ray spectrometry for the determination of 210Pb

A well High purity germanium (HPGe) gamma spectrometer with NaI(Tl) Compton anticoincidence shield recently installed at DTU Nutech and specially designed for low-level measurements was used for the 210Pb determination in environmental samples. The system is compared to standard stand-alone HPGe spectrometers. The choice between high efficiency well and planar detectors as well as optimum sample size depending on available sample quantity are discussed. Results show that the only comparative advantage of the well anticoincidence system is when just small sample sizes are available.

Modeling of low-energy charged particles passage through GAMMA-400 gamma-telescope thermal insulation and two- layer plastic scintillation detectors used as anticoincidence shield

The results of low-energy charged particles passage through GAMMA-400 gamma- telescope thermal insulation and two-layer plastic scintillation detectors used as anticoincidence shield are presented. An existing GEANT4 GAMMA-400 model is used. Effects of thermal insulation on charged particle passage are investigated. These results will be used to testing the effect of low-energy charged particles flux on GAMMA-400 gamma-quanta registration capabilities. Sufficiently large energy deposition in two-layer plastic anticoincidence scintillation detectors might interfere with high-energy particle registration and identification. However, GAMMA-400 detection capabilities are not affected by this, as the energy deposition in the lower layer of S3 is less than 1.5 MeV in all simulated cases. This value is less than threshold for high energy particles identification start (2.5 MeV). It makes impossible to incorrectly identify a low-energy charged particle energy deposition as backsplash from a high-energy gamma-quantum.