Γ-ray Detector Research Articles

Unveiling the Monoclinic Phase in CsPbBr3-xClx Perovskite Crystals, Phase Transition Suppression and High Energy Resolution γ-Ray Detection.

All-inorganic CsPbBr3 and CsPbCl3 perovskites are promising materials for high-performance solar cells and advanced radiation detection technologies with high stability. Here we report that CsPbBr3-xClx (x = 0-3) crystals exhibit eutectoid behavior for the melting points and phase transition temperatures. The well-known halide perovskite cubic phase transition temperature shifts near room temperature (∼37 °C for CsPbBr2Cl). We conducted an extensive crystallographic analysis on single crystals of 7 different compositions, including the end members CsPbBr3 and CsPbCl3. Contrary to previous beliefs, we discovered they exhibit a monoclinic structure with space group symmetry P21/m at room temperature, rather than the orthorhombic Pnma. This new structural model is more precise and features a unit cell volume that is four times larger than that of the orthorhombic model. From high-quality single crystals of CsPbBr2Cl, grown by the Bridgman method, we constructed γ-ray detectors achieving an energy resolution of 7.2% at 200 V for 57Co radiation. Thermally stimulated current spectroscopy of the CsPbBr2Cl samples revealed that the defect densities in crystals from different regions of the ingot were relatively uniform, with values of ∼4.72 × 1012 and ∼5.09 × 1012 cm-3. These findings indicate that low deep-level defect densities can be achieved that are consistent with the notable performance of the CsPbBr2Cl perovskite as a high-energy γ radiation detector.

Microstructure evolution of CdZnTe crystals irradiated by heavy ions

Consideration of irradiation effects is important for in-orbit operation and radiation protection in aerospace applications. The configuration of irradiation defects and their impact on deteriorating the carrier transport properties of CZT crystals need to be clarified. In this study, the microdefect evolution mechanism of CdZnTe (CZT) crystals under 10 MeV Chlorine (Cl) ion irradiation at flux of 1×1010∼1×1012 n·cm-2 are investigated. The stacking faults first appear in the CZT crystal at 4.5×10-4 displacement per atom (dpa), which are categorized into slip-type, gap-type and vacancy-type. In order to hinder the further expansion of stacking fault, S-shaped stacking fault dipole appears. When the dpa reaches 4.5×10-2, the local phase transition occurs in the damage zone to form CuPt-A ordered phase with ZnTe/CdTe periodic arrangement because the fluctuation in local composition and strain caused by cascade collisions. The deterioration of electric field distribution and charge collection caused by irradiation damage layer leads to the decrease of γ-ray detection ability. The energy resolution (ER) of the CZT detector for γ-ray can be maintained at 30.6% when the ion flux accumulates to 1×1012 n·cm-2, revealing high irradiation hardness. Consequently, these findings provide a theoretical basis for the radiation damage recovery of CZT detectors, further demonstrating that CZT crystals are the most competitive new generation of room-temperature nuclear radiation detection materials, and can provide radiation protection strategies for similar compound semiconductor materials.

Is Gamma-Ray Burst 221009A Really a Once-in-10,000 yr Event?

Gamma-ray bursts (GRBs) brighter than the GRB 221009A, the brightest yet observed, have previously been estimated to occur at a rate of one per 10,000 yr, based on the extrapolation of the distribution of fluences of the long-GRB population. We show that bursts this bright could instead have a rate as high as approximately one per 200 yr if they are from a separate population of narrow-jet GRBs. This population must have a maximum redshift of about z ≈ 0.38 in order to avoid overproducing the observed rate of fainter GRBs. We show that it will take ≳100 yr to confirm this new population based on observing another GRB from it with a γ-ray detector; observing an orphan optical afterglow from this population with Vera Rubin Observatory or an orphan radio afterglow with the Square Kilometer Array will also take similarly long times to observe, and it is unclear if they could be distinguished from the standard GRB population. We show that the nearby narrow-jet population has more favorable energetics for producing ultra-high-energy cosmic rays than standard GRBs. The rate of bursts in the Milky Way bright enough to cause mass extinctions of life on Earth from the narrow-jet population is estimated to be approximately one per 500 Myr. This GRB population could make life in the Milky Way less likely, with implications for future searches for life on exoplanets.

Photodiodes Made of Cascade Perovskite Single Crystals with Passivation Layers for High-Energy-Resolution γ-ray Spectroscopy.

Lead halide perovskite single crystals (LHPSC) are promising for room-temperature γ-ray spectroscopy in radiation detection. While MA(CH3NH3)-based LHPSCs are the most straightforward and cost-effective to synthesize from solution, their performance in γ-ray spectroscopy is hindered by significant noise and ion migration at high bias, which degrades their energy resolution (ER). The work introduced an n-type/intrinsic/n-type photodiode incorporating passivation layers of MA-based LHPSCs, grown through solution-process epitaxial growth. This single-polarity device demonstrated an outstanding ER of 3.6% for 662 keV γ-ray photons. Overall, this work provides useful information for developing room-temperature γ-ray detectors based on solution-processed lead halide perovskites.

Formation of GW230529 from Isolated Binary Evolution

In this paper, we explore the formation of the mass-gap black hole-neutron star (mgBHNS) merger detected in gravitational wave (GW) event, i.e., GW230529, from the isolated binary evolution channel, and study potential signatures of its electromagnetic counterparts. By adopting the “delayed” supernova prescription and reasonable model realizations, our population synthesis simulation results can simultaneously match the rate densities of mgBHNS and total BHNS mergers inferred from the population analyses, along with the population distribution of the BH mass in BHNS mergers reported by the LIGO–Virgo–KAGRA Collaboration. Because GW230529 contributes significantly to the inferred mgBHNS rate densities, we suggest that GW230529 can be explained through the isolated binary evolution channel. Considering the AP4 (DD2) equation of state, the probability that GW230529 can make tidal disruption is 12.8% (63.2%). If GW230529 is a disrupted event, its kilonova peak apparent magnitude is predicted ∼23–24 mag, and hence, can be detected by the present survey projects and Large Synoptic Survey Telescope. Since GW230529 could be an off-axis event inferred from the GW observation, its associated gamma-ray burst (GRB) might be too dim to be observed by γ-ray detectors, interpreting the lack of GRB observations. Our study suggests the existence of mgBHNS mergers formed through the isolated binary evolution channel due to the discovery of GW230529, indicating that BHNS mergers are still likely to be multimessenger sources that emit GWs, GRBs, and kilonovae. Although mgBHNS mergers account for ∼50% of the cosmological BHNS population, we find that ≳90% of disrupted BHNS mergers are expected to originate from mgBHNS mergers.

Novel compositionally disordered (Pb,Sr)WO4 single-crystalline scintillation material for X- and gamma-ray scanners

Heavy, bright, and fast single-crystalline scintillation material (Pb,Sr)WO4 was produced and characterized for the first time. Incongruently melted material was obtained by the solution-melt method under the conditions of spontaneous crystallization. It has a density of 7.3 g/cm3 and an effective charge of Zeff = 71. The scintillation kinetics are characterized by a decay constant of 490 ns, while the light yield of scintillation is measured to be 13 500 ph/MeV, both at room temperature. A fabrication of the new low-temperature melting single crystalline tungstate family’s material opens the door for better and cheaper scintillators for X-ray and γ-ray detectors, in particular for radiographic scanners and medical imaging devices.

Growth and characterization of highly efficient Cs[formula omitted]Cu[formula omitted]I[formula omitted] single crystal for [formula omitted]-ray detection

Metal halide perovskites, particularly zero-dimensional (0D) variants, have garnered significant attention as scintillator materials for various applications such as γ-ray spectroscopy, X-ray imaging, and security. Among these, Cs3Cu2I5 has emerged as a promising candidate owing to its exceptional characteristics, such as good energy resolution, high light output, and high stopping power. Although there is sufficient data available on the scintillation properties of Cs3Cu2I5 Single Crystal (SC) grown using various methods, there still remains a scarcity of data on the scintillation properties of SCs grown using solvent evaporation method at room temperature. In the present work, Cs3Cu2I5 SCs have been grown using the solvent evaporation method at room temperature and characterised for their structural, optical, and scintillation properties. The SC shows an orthorhombic structure with a bandgap of 3.58 eV. The optical properties of the SC reveal the existence of Self-Trapped Exciton (STE). The SC exhibits an energy resolution of 5.80 ±0.05% at 662 keV and a light output of 41,000 photons/MeV, making it suitable for γ-rays detection. The intrinsic photopeak efficiencies of Cs3Cu2I5 SC for γ-rays are reported for the first time. GEANT4 simulation toolkit has been used to perform realistic simulations, and the simulated and experimental efficiencies are compared. Simulations show that Cs3Cu2I5 scintillator has twice the efficiency of the NaI:Tl scintillator.

High transparency Ce3+-doped oxyfluoride glass scintillator for X-ray imaging and γ-ray detection

High transparency Ce3+-doped dense gadolinium aluminum borosilicate (GSx) glass scintillator was synthesized in reducing atmosphere by melt-quenching process. The transmittance of the glasses exceeds 80%, and the light attenuation length is between 5-20 cm within the range of 400–600 nm. GSx glass shows an photoluminescence (PL) in range of 350–550 nm, with the strongest emission peak around 420 nm. The PL decay time of GSx glasses is around 37 ns, with a maximum PL quantum yield of 44.05%. The integrated X-ray excited luminescence (XEL) intensity of GSS glass is 52.5% compared with BGO crystal. For X-ray imaging, GSL glass based imaging system shows a high spatial resolution of 9 lp/mm, which is comparable to CsI:Tl X-ray detectors. Under γ-ray, the highest light yield of GSS glass is 1235 ph/MeV with an energy resolution of 24.0% at 662 keV, close to that of BSO crystal. The scintillation decay time of GSx glasses is consisted of fast (∼100 ns) and slow (∼560 ns) components. In thermally stimulated luminescence (TSL), GSS glass exhibits a strong TSL peak at approximately 440 K, with low intensity shoulders at about 520 K, implying different types of defects and traps. Therefore, GSx glass has promising prospects for X-ray imaging and high-energy physics applications.

Scintillator application of CsPbBr3 quantum dots-embedded SiO2 glasses

CsPbBr3 quantum dots-embedded SiO2 glasses were synthesized by the spark plasma sintering method as novel scintillators for γ-ray detectors. Their optical and scintillation properties were investigated to examine the scintillation performance. The X-ray diffraction patterns observed a halo peak of the SiO2 glass phase and diffraction peaks of CsPbBr3. An emission peak due to CsPbBr3 quantum dots was detected at around 515 nm in both photoluminescence (PL) and scintillation spectra. The PL and scintillation decay time curves included a component of nanosecond order, resulting from CsPbBr3 quantum dots. Under γ-ray irradiation from 137Cs, the light yield (LY) of the 0.2% CsPbBr3-embedded SiO2 glass was 150 photons MeV−1.

Geant4 simulations for the [formula omitted]-ray detectors of gSPEC at GSI/FAIR

A design study for the γ-ray detector array of the gSPEC project, which aims at measuring nuclear moments at GSI/FAIR, is presented. Foreseen setups, involving DEGAS and the new gDEGAS triple cluster detectors for γ-ray spectroscopy are simulated using the Geant4 framework. The main characteristics associated to these detector assemblies with the envisaged configurations, namely the photo-peak efficiency and the angular resolution, are discussed. A new correction procedure for a better reconstruction of the time-perturbed angular distribution is proposed.

A γ-Ray-emitting Blazar at Redshift 3.64: Fermi-LAT and OVRO Observations of PKS 0201+113

High-redshift (z > 3) γ-ray blazars are rare, but they are crucial for our understanding of jet evolution, γ-ray production and propagation, and the growth of supermassive black holes in the early Universe. A new analysis of Fermi-LAT data reveals a significant (5σ), spectrally soft (Γ ≃ 3.0) γ-ray source in a specific 4 month epoch, cospatial with PKS 0201+113 (z = 3.64). Monitoring of PKS 0201+113 at 15 GHz by the Owens Valley Radio Observatory 40 m telescope from 2008 to 2023 shows a prominent flare that dominates the radio light curve. The maximum of the radio flare coincides with the γ-ray flare, strongly suggesting an association (p-value = 0.023) between the γ-ray and the radio sources. PKS 0201+113 is only the third γ-ray blazar to be identified with z > 3.5, and it is the first such object to be identified by the detection of quasi-simultaneous γ-ray and radio flares. The jet properties of this peculiar blazar have been investigated. A detailed study of a two-zone leptonic model is presented that fits the broadband spectral energy distribution. An alternative scenario is also briefly discussed.

Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh95

Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research () Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian. Published by the American Physical Society 2024

Cold-Sintered All-Inorganic Perovskite Bulk Composite Scintillators for Efficient X-ray Imaging.

Cost-effective bulk scintillators with high density, large-area, and long-term stability are desirable for high-energy radiation detections. Conventional bulk polycrystalline or single-crystal scintillators are generally synthesized by high-temperature approaches, and it is challenging to realize simultaneously high detectivity/responsivity, spatial resolution, and rapid time response. Here, we report the cold sintering of bulk scintillators (at 90 °C) based on an "emitter-in-matrix" principle, in which emissive CsPbBr3 nanocrystals are embedded in a durable and transparent Cs4PbBr6 matrix. These bulk scintillators exhibit high light yield (33,800 photons MeV-1), low detection limit (79 nGyair s-1), fast decay time (9.8 ns), and outstanding spatial resolution of 8.9 lp mm-1 to X-ray radiation and an energy resolution of 19.3% for γ-ray (59.6 keV) detection. The composite scintillator also shows exceptional stability against environmental degradation and cyclic X-ray radiation. Our results demonstrate a cost-effective strategy for developing perovskite-based bulk transparent scintillators with exceptional performance and high radioluminescence stability for high-energy radiation detection and imaging.

Evidence of the γ-ray counterpart of nova FM Cir from Fermi–LAT

ABSTRACT We report the results of an analysis of X-ray and γ-ray data from the nova FM Cir taken by Swift and Fermi–LAT. The γ-ray emission from FM Cir can be identified with a significance level of ∼3σ within ∼40 d after the nova eruption (2018 January 19) when we bin the light curve per day. The significance can exceed the 4σ confidence level if we accumulate a longer time (i.e. 20 d) to bin the light curve. The γ-ray counterpart could be identified with a Test Statistic (TS) above 4 until ∼180 d after the eruption. The duration of the γ-ray detection is longer than those reported in previous studies of other novae detected in the GeV range. Significant X-ray emission was observed after the γ-ray flux level fell below the sensitivity limit of Fermi–LAT. The hardness ratio of the X-ray emission decreased rapidly with time, and the spectra were dominated by blackbody radiation from the hot white dwarf. Except for the longer duration of the γ-ray emission, the multiwavelength properties of FM Cir closely resemble those of other novae detected in the GeV range.

Ionic Conduction-Based Polycrystalline Oxide Gamma Ray Detection - Radiation-Ionic Effects.

Newly discovered opto-ionic effects in metal oxides provide unique opportunities for functional ceramic applications. The authors generalize the recently demonstrated grain boundary opto-ionic effect observed in solid electrolyte thin films under ultraviolet (UV) irradiation to a radiation-ionic effect that can be applied to bulk materials and used for gamma-rays (γ-rays) detection. Near room temperature, lightly doped Gd-doped CeO2, a polycrystalline ion conducting ceramic, exhibits a resistance ratio change ≈103 and reversible response in ionic current when exposed to 60Co γ-ray (1.1 and 1.3 MeV). This is attributed to the steady state passivation of space charge barriers at grain boundaries, that act as virtual electrodes, capturing radiation-induced electrons, in turn lowering space charge barrier heights, and thereby exclusively modulating the ionic carrier flow within the ceramic electrolytes. Such behavior allows significant electrical response under low fields, that is, < 2 V cm-1, paving the way to inexpensive, sensitive, low-power, and miniaturizable solid-state devices, uniquely suited for operating in harsh (high temperature, pressure, and corrosive) environments. This discovery presents opportunities for portable and/or scalable radiation detectors benefiting geothermal drilling, small modular reactors, nuclear security, and waste management.

Simultaneous Gamma-Neutron Vision device: a portable and versatile tool for nuclear inspections

This work presents GN-Vision, a novel dual γ-ray and neutron imaging system, which aims at simultaneously obtaining information about the spatial origin of γ-ray and neutron sources. The proposed device is based on two position sensitive detection planes and exploits the Compton imaging technique for the imaging of γ-rays. In addition, spatial distributions of slow- and thermal-neutron sources (<100 eV) are reconstructed by using a passive neutron pin-hole collimator attached to the first detection plane. The proposed gamma-neutron imaging device could be of prime interest for nuclear safety and security applications. The two main advantages of this imaging system are its high efficiency and portability, making it well suited for nuclear applications were compactness and real-time imaging is important. This work presents the working principle and conceptual design of the GN-Vision system and explores, on the basis of Monte Carlo simulations, its simultaneous γ-ray and neutron detection and imaging capabilities for a realistic scenario where a 252Cf source is hidden in a neutron moderating container.

Gamma/Hadron Separation Method for the HADAR Experiment

Ground-based arrays of imaging atmospheric Cherenkov telescopes (IACTs) are the most sensitive γ-ray detectors for energies of approximately 100 GeV and above. One such IACT is the High Altitude Detection of Astronomical Radiation (HADAR) experiment, which uses a large aperture refractive water lens system to capture atmospheric Cherenkov photons (i.e., the imaging atmospheric Cherenkov technique). The telescope array has a low threshold energy and large field of view, and can continuously scan the area of the sky being observed, which is conducive to monitoring and promptly responding to transient phenomena. The process of γ-hadron separation is essential in very-high-energy (>30 GeV) γ-ray astronomy and is a key factor for the successful utilization of IACTs. In this study, Monte Carlo simulations were carried out to model the response of cosmic rays within the HADAR detectors. By analyzing the Hillas parameters and the distance between the event core and the telescope, the distinction between air showers initiated by γ-rays and those initiated by cosmic rays was determined. Additionally, a Quality Factor was introduced to assess the telescope’s ability to suppress the background and to provide a more effective characterization of its performance.

Activation level of the concrete building and pressure vessel in JAEA-Tokai tandem accelerator

ABSTRACT The activation level of the JAEA-Tokai tandem accelerator facility was investigated experimentally in advance of the future decommissioning. JAEA-Tokai tandem accelerator facility has a higher terminal voltage of 18 MV and a larger total floor area, Compared to other electrostatic accelerators with terminal voltage of 1 MV to 6 MV. Therefore, determination for ‘where,’ ‘what,’ and ‘how many’ nuclides are produced in the facility is crucial. Thermal neutrons generated by beam losses associated with accelerator operations contribute significantly to the activation of equipment and facilities. The accumulated activities of60Co and152Eu; the most considerable radionuclides at the decommissioning, can be deduced by the thermal neutron fluence rate during the accelerator operation. In this study, thermal neutron fluence measurement on the surface of the pressure vessel and concrete building was conducted with conventional methods using dosimeters and metal foil detectors as well as a new method using a portable γ-ray detector. The thermal neutron fluence in the facility during the accelerator operation ranges from 101 to 104 n/cm2/s. The sum of deduced activities of60Co and152Eu in 50 years is much lower than the clearance level of 0.1 Bq/g in all areas except in the irradiation room.

The invisible black widow PSR J1720-0534: implications for the electron density towards the North Polar Spur

Abstract Radio emission from pulsars can be used to map out their distances through dispersion measure (DM), which quantifies the amount of radio pulse dispersion. However, this method relies on accurately modeling the free electron density in the line of sight. Here, we present a detailed study of the multi-wavelength emission from PSR J1720-0534, a black widow compact binary millisecond pulsar discovered in 2021, which the latest electron density model of the Galaxy (YMW16; Yao et al. 2017) places at only 191 pc. We obtained and analyzed deep multi-wavelength observations in the γ-ray (Fermi-LAT, 2008-2022), optical (LCO, 2.7-h), near-infrared (NOT, 3.5-h) and X-ray (Swift-XRT, 10 ksec) bands. We found no significant detection of γ-ray, optical, near-infrared, or X-ray counterparts around the radio-timing position of PSR J1720-0534, which we thus nickname ‘the invisible black widow’. Employing the most constraining near-infrared limit (J &amp;gt; 23.4 mag), we established a lower limit on the source distance, d &amp;gt; 1.1 kpc, assuming conservative properties for the black widow companion star. This distance lower limit differs drastically (by a factor of more than five) from the YMW16 DM distance estimate. We attribute this difference to the inclusion in the YMW16 model of a large and dense component towards the North Polar Spur. Considering our results and recent parallax distances to other pulsars in this direction, we argue that such a local and large component in the electron density model of the Galaxy is unnecessary.

Response of LaBr2.85Cl0.15:Ce, LaBr[formula omitted]:Ce and NaI:Tl crystals to fast and thermal neutrons

This communication reports the measurement of direct response for fast and thermal neutrons of a newly marketed scintillation crystal LaBr2.85Cl0.15:Ce, along with the widely used LaBr3:Ce and NaI:Tl crystals. It continues our investigation on the possible utility of LaBr2.85Cl0.15:Ce crystal for the detection of high-energy γ-rays and neutrons. This is the first report of the neutron response of the LaBr2.85Cl0.15:Ce crystal. The neutron response was measured for the three detectors using a calibrated Am-Be source, which emits both neutrons and γ-rays. To eliminate the events due to the interaction of the 4.4 MeV γ-ray emitted from Am-Be, the γ-ray response of all three crystals was simulated using the Monte Carlo simulation toolkit GEANT4. Events due to 2.22 MeV γ-ray produced by the capture of thermal neutrons in the paraffin moderator were also eliminated with the aid of simulations. In addition, the response due to fast neutrons was also simulated using GEANT4 and compared with the measured spectrum. This is the first report of the simulation of fast neutron response of LaBr2.85Cl0.15:Ce using GEANT4. The fast neutron detection efficiency of the three detectors has been obtained from the measured spectra.