keV Γ-rays Research Articles

Interface Energy-Level Reorganization for Efficient Perovskite γ-Ray Detectors.

Metal halide perovskites are promising candidates for gamma-ray (γ-ray) spectrum detectors. However, achieving high-resolution energy spectra in single-photon pulse-height analysis mode remains challenging, due to the inevitable leakage currents degrade the recognizable fingerprint energies which is critical for resolving γ-ray spectroscopy. We demonstrate under high bias voltage, a deficient contact barrier can lead to excessive surface charge injection, thereby increasing leakage current from electrodes to perovskites. Hence, we conceive to employ surface ligand engineering on perovskite single crystals to manipulate energy levels to suppress leakage current. In particular, anchoring a strong dipole ligand onto the perovskite induced surface charge-density displacement, leading to a downward band bending and heightened the corresponding contact barrier. Consequently, the strategy minimized the detectors' leakage current by an order of magnitude, to as low as 44 nA cm-2 at -100 V. The resulting detectors show a significant improvement in energy resolution, 3.9 % for 22Na 511 keV γ-rays has been achieved at room temperature. The resulting detector further resolves each fingerprint energy for 152Eu γ-spectrum, representing one of the best γ-rays perovskite detectors reported to date. Moreover, the detectors exhibited stabilized energy resolution without any degradation under a continuous electric field (1,000 V cm-1) for over 300 minutes, representing the longest longevity reported to date.

Multifunctional Ta4C3Tx MXene/HTPP - PBS composites with multi cross-linking systems to cope with complex nuclear environments

The development of multifunctional radiation protection materials is crucial to ensure the safety of personnel and equipment in complex nuclear environments. Herein, a flexible radiation protection material integrating self-healing, thermal management, and behaviour response was prepared from Ta4C3Tx MXene, Hydrogen-terminated phenyl polysiloxane, and Polyborosiloxane through esterification, “thiol-ene click” hydrosilylation reaction using L(+)-Cysteine as a bridge. The results showed that when Ta4C3Tx MXene reached 20 wt%, the tensile strength of composite was 0.6321 MPa with the self-healing rate at 90.22 %. And the gauge factor of the material reached 25.83 at 100 % strain. This compensated for the gap between low strain and high sensitivity. Additionally, the multilayer structure of Ta4C3Tx MXene and the absorption properties of Tantalum enable the material to attenuate γ-rays through absorption and scattering mechanisms. The attenuation capability of Ta2O5 and Ta4C3Tx MXene fillers for 59.6 KeV γ-rays was compared at the same Tantalum content. When the Tantalum content reaches 23.81 wt%, the Ta4C3Tx MXene composite contains 20 wt% filler and has an attenuation coefficient of 0.757. Similarly, the Ta2O5 composite contains 22.5 wt% filler and has an attenuation coefficient of 0.734. These results are significant for improving temperature and behaviour monitoring of workers in low-temperature nuclear environments.

Novel LaCl3:Yb2+ crystal scintillator for X-ray spectrometer

This work investigated the growth, optical properties, and scintillation performance of a LaCl3 single crystal doped with Yb2+ ions. The crystal was grown using the vertical Bridgman method. The photoluminescence spectrum resembled the X-ray induced luminescence spectrum, indicating emission from the 5d→4f transition of Yb2+. LaCl3:Yb2+ exhibited an energy resolution of 14.3% and a light output of 24,940 ph/MeV under 662 keV γ-ray excitation. Additionally, the scintillation decay profiles were measured using alpha particles and gamma rays from 241Am and 137Cs sources, respectively. These results suggest that Yb2+ could be a promising luminescence center for high light yield scintillation detectors.

Electronic properties and quantitative mapping of magnetic moments of rare-earth hard magnet SmCo5: First principles computations and inelastic scattering

Looking at the limitations of neutron spectroscopy in exploring properties of rare earth hard magnet SmCo5, inelastic scattering for charge and magnetic Compton profiles are attempted. The experimental momentum densities using 661.65 keV γ-ray energy are compared with the theoretical Compton profiles (CPs) deduced using linear combination of atomic orbitals (LCAO) with different exchange and correlation potentials and also spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) calculations. The anisotropies in the computed CPs, along the principal directions, show high momentum densities along the c-axis [00.1] of SmCo5 than [10.0] and [11.0] directions. An overall better agreement of CP computed using LCAO-GGA and that from experiment is observed which shows more appropriateness of GGA-PBE scheme for the exchange and correlation energies for SmCo5. The small value of charge transfer from Sm → Co and positive value of overlap Mulliken population dictate dominance of covalent bonding in SmCo5. Moreover, available experimental data on c-axis oriented magnetic CP (MCP) of SmCo5 have been compared with the present SPR-KKR calculations. It is seen that present SPR-KKR based MCP is in resemblance with the available experimental MCP. A decomposition of experimental MCP in to its constituent profiles depict that the spin momentum of Co and Sm are aligned anti-parallel while the diffuse contribution aligns opposite to the absolute spin moment. Comparison of amplitude and direction of site specific spin moments in SmCo5 is made with the present SPR-KKR and available experimental and theoretical data.

Intensely bonded high filling bismuth oxide with chloroprene rubber to achieve lead-free flexible materials for γ-rays shielding

Achieving lead-free flexible materials with excellent γ-ray shielding as well as good mechanical properties are of significance to radiation protection safety and wear comfort of wearable articles. In this paper, polydopamine (PDA) is coated on Bi2O3 particles to form a typical core–shell structure Bi2O3@PDA, which is used to intensely bond bismuth oxide (Bi2O3) with chloroprene rubber (CR). It promotes the interface interaction between Bi2O3 and CR matrix, leading to the uniform dispersion of the filler and rich interfacial compatibility in CR/Bi2O3@PDA composite with as high as 50 wt% filling. Furthermore, 50 wt% CR/Bi2O3@PDA composite displays 53.6% shielding rate for 105 keV γ-rays. Meanwhile, its tensile strength and elongation at break are 9.6 MPa and 1424.8%, respectively, which are without sacrificing too much in comparison with the neat rubber. We propose a versatile route to prepare superior integrated properties of flexible materials, which can be used as wearable articles for radiation shielding.

Single-layer Compton camera based on a 1 mm thick pixelated CDTE detectors

Compton camera is a novel γ-camera paradigm that relies upon the kinematics of Compton scattering for image reconstruction. A Conventional Compton camera uses two layers of sensors - the Absorber and the Scatterer. This work reports the proof of concept of a single-layer Compton camera (SLCC) where simultaneous Compton pairs events are registered in a single High-Z semiconductor sensor. The Hybrid pixel detector (HPD) is 1 mm thick, 256 x 256 square pixels with 55 μm pixel pitch CdTe sensor bonded to a Timepix3 readout ASIC. The superior spectroscopic imaging and fast timing capabilities of the Timepix3 readout ASIC coupled with a microscopic and highly pixelated CdTe enable simultaneous event detection of multi-energies occurring at multiple positions. The concept was exemplified by measuring the 122 KeV γ-ray emitted from a 57Co radioisotope source at two positions. Data were captured in the Timepix3 data-driven mode with the KATHERINE readout system via Gigabyte Ethernet data transfer. A bespoke Compton kinematics criterion algorithm implemented in Python 3 IDE was used for data analysis and Compton’s image reconstruction. Numerous events (5.2 million) were captured for 30-minute acquisitions. However, due to the thin nature of CdTe, fewer events (≈ 0.01 %) met the Compton event selection criteria. Nevertheless, the algorithm accurately pinpointed the radioisotope’s location, demonstrating proof of concept of the SLCC system.

Luminescence and scintillation properties of fast Ce,Mg:Lu2YGaxAl5-xO12 ceramic scintillators fabricated from co-precipitated powders

Ce,Mg:Lu2YGaxAl5-xO12 (x = 1.5, 2, 2.5, 3) ceramic scintillators were fabricated by oxygen sintering combined with air annealing using nano-powders synthesized by the co-precipitation method. The Ce3+ 5d1 → 4f (2F5/2, 2F7/2) luminescence band was blue shifted with increasing Ga content due to the decrease in the crystal field splitting of the 5d levels. At room temperature (RT), the decrease of photoluminescence decay time and scintillation decay time was observed with increasing Ga content. At 662 keV γ-rays, the sample Ga2 exhibited high light yield (LY) of 28,700 photons/MeV, fast scintillation decay times of 17.7 ns (17 %) + 45.7 ns (83 %), and good time resolution of ∼220 ps. At RT, the decrease of LY value for the samples Ga2.5 and Ga3 could be attributed to the larger thermal ionization of the excited Ce3+ centers.

Structural, morphological, thermal, mechanical, positron annihilation, and γ-ray shielding studies of nano-tungsten oxide/polyvinyl alcohol composites

Tungsten oxide nanoparticles were synthesized. Metal/polymer composites of nano-sized WO3 and poly vinyl alcohol were blended by the casting method with concentrations of WO3. The structural, morphological, thermal, and mechanical characteristics of the prepared samples were investigated. The γ-ray attenuation properties of the synthesized composites were examined using γ-ray spectrometers, and the γ-ray mass absorption coefficients were measured using 662 keV γ-ray of 137Cs radioactive source. The defects and microstructure changes of the composites were probed using positron annihilation lifetime and Doppler broadening techniques. The shielding performance and thermal stability improved with increasing the concentration of WO3, and some of the mechanical properties, in particular the elongation at break, deteriorate. The contribution of WO3 has a strong effect on reducing the relative fractional free volume, which in turn helps to increase the γ-ray absorption of the composites. The use of a 50–70 % WO3/PVA composite is recommended.

Test of 116CdWO4 and Li2MoO4 scintillating bolometers in the CROSS underground facility with upgraded detector suspension

In preparation for the CROSS experiment to search for double-beta (2β) decay of 100Mo, we upgraded a low-background facility at the Canfranc underground laboratory (Spain) by installing a magnetic damping-based detector suspension inside a pulse-tube cryostat. We tested the suspension in low-temperature (15 mK) measurements with two scintillating bolometers made of large-volume crystals of 116CdWO4 (reference of the set-up) and Li2MoO4 (R&D of the CLYMENE project in view of the CUPID 2β experiment), each coupled to a thin Ge bolometric light detector. Despite the evidence of a residual pulse-tube-induced noise, picked up by cabling, we achieved high performance with all tested devices. In particular, the energy resolution for 2615 keV γ-ray measured with both 116CdWO4 and Li2MoO4 bolometers is ∼6 keV FWHM, among the best-reported results for thermal detectors based on such compounds representing a great interest to searches for 2β decay in 116Cd (Q-value is 2813 keV) and 100Mo (3034 keV) respectively. Highly efficient particle identification (α vs. β/γ) is achieved also with the scintillating bolometer made of a low light yield crystal (Li2MoO4), thanks to the low noise (10 eV RMS) exhibited by the light detector exploiting the Neganov-Trofimov-Luke effect for signal amplification. We also found a rather high level of radiopurity in the Li2MoO4 crystal; only traces of 210Po and 226Ra were detected (∼0.1 mBq/kg each), while the 228Th activity is expected to be at least an order of magnitude lower, as well as a 40K activity is below 6 mBq/kg.

Long-term stability of hydroxyapatite bone phantoms for the calibration of in vivo x-ray fluorescence spectrometry-based systems of bone lead and strontium quantification

Hydroxyapatite (HAp) phantoms have been proposed as an alternative to plaster of Paris (poP) phantoms for the calibration of x-ray fluorescence-based systems for the in vivo quantification of bone lead and strontium which employ a coherent normalization procedure. The chemical composition of the material becomes critical in the calculation, or omission, of the coherent correction factor (CCF) required in this normalization procedure. This study evaluated the long-term chemical stability of HAp phantoms. Phantoms were prepared and allowed to age for a two week period and over a seven year period in ambient conditions. The chemical composition of the phantoms was then assessed by powder x-ray diffraction. Two week old phantoms were found to be composed of HAp with only a small amount of contamination from CaHPO4·2H2O. Seven year old phantoms were found to have converted nearly completely to a carbonate-bearing apatite in the form of Ca10(PO4)6(CO3)0.75(OH)0.5 indicating that the HAp phantom material likely reacts with carbon dioxide in air over time forming a carbonate-bearing apatite. The influence of this chemical conversion was assessed at the level of relevant cross-sections. Calibration under the assumption that the material is HAp when in fact it is a carbonate-bearing apatite would result in not more than a 0.2%–2% bias in the total mass attenuation coefficient within the photon energy range of 0–100 keV. Differential scattering cross-section for coherent scattering was found to differ between HAp and carbonate-bearing apatite by 0.9%–2% for both a 35.5 keV and 88.0 keV γ-ray. This variation in the differential scattering cross-section for coherent scattering may introduce a ca. 2% bias in the CCF used within the coherent normalization-based calibration procedure. Using HAp phantoms as calibrators thus requires acknowledgement of this conversion in chemical form and possible introduction of uncertainty into the calibration procedure.

Hardware, methodology and applications of 2+D backscatter Mössbauer spectroscopy with simultaneous x-ray and γ-ray detection

A unique method is presented for the acquisition and analysis of 57Fe backscatter Mössbauer spectra with simultaneous detection of the resonant 14.4 keV γ-rays and the characteristic 6.4 keV x-rays, using a custom-built multi-parameter analyser constructed on the basis of commercial analogue to digital converters and high-speed digital latches. The system allows for the simultaneous registration of Doppler-modulation velocities and photon energies, with up to 4096 and 8192 digital channels respectively. This arrangement is in contrast to most related systems, which detect at a single narrow energy window per detector. Samples of arbitrary atomic structure, morphology and surface topography can be studied without altering the setup or the analysis procedure, provided that the samples are at least micrometre sized. The hardware and software that are used to acquire data with minimal dead time are described and the custom and self-contained methods for post-measurement energy discrimination, background correction and velocity-axis folding are discussed. The data are fit using a general Hamiltonian model for the nuclear energy levels of 57Fe and a quantum mechanical description of the angular momentum coupling is utilised, with consideration of the crystalline and chemical disorder of the sample under examination. Three examples of distinct magnetic systems, with thicknesses ranging from m to 6 mm, that were studied using this method are presented, these are: an amorphous CoFeB-based ribbon with ultra-soft coercivity for high-frequency applications, magnetically hard Nd-Fe-B thick films on Si substrates, examined in both as-deposited and annealed states, and a sample from the nickel-rich iron meteorite NWA 6259 that contains the atomically ordered, elevated coercivity, phase of FeNi, tetrataenite. The wide applicability and usefulness of this method is thus demonstrated on three distinct sample morphologies that required little to no surface preparation prior to examination.

High temperature X-ray and γ-ray spectroscopy with a diamond detector

A single crystal chemical vapour deposition diamond detector was electrically characterised and then investigated as a spectroscopic photon counting X-ray and γ-ray detector across the temperature range, T, −20 °C ≤ T ≤ 100 °C. The detector was connected to a custom-built charge-sensitive preamplifier of low electronic noise and illuminated in turn by 55Fe radioisotope X-ray and 109Cd radioisotope X-ray and γ-ray sources. In combination, the radiation sources provided characteristic soft (e.g. 5.9 keV) and hard (e.g. 22.16 keV) X-rays and 88.03 keV γ-ray emissions. The Mn Kα (5.9 keV) and Kβ (6.49 keV) X-ray emissions from the 55Fe radioisotope X-ray source were detected (and separated from the zero energy noise peak) at temperatures of −20 °C ≤ T ≤ 60 °C; the Ag Kα (22.16 and 21.99 keV) and Kβ (24.94, 24.99, and 25.46 keV) X-ray emissions and 88.03 keV γ-ray emissions were detectable across the entire temperature range investigated (−20 °C ≤ T ≤ 100 °C). The detector and the preamplifier were operated without cooling across the entire temperature range. The energy resolution (full width at half maximum) at 22.16 keV (Ag Kα1) was 4.57 keV ± 0.26 keV at 100 °C and 2.70 keV ± 0.18 keV at −20 °C. Noise analysis indicated that the combination of dielectric noise and any incomplete charge collection noise present dominated the other noise components at 5.9 keV. When the detector was illuminated with the 109Cd radioisotope X-ray and γ-ray source, a high count rate introduced parasitic effects (possibly baseline shift) which reduced the optimum shaping time of the spectrometer.

Analyzing the neutron and γ-ray emission properties of an americium–beryllium tagged neutron source

Americium–beryllium (AmBe), a well-known tagged neutron source, is commonly used for evaluating the neutron detection efficiency of detectors used in ultralow background particle physics experiments, such as reactor neutrino and diffuse supernova neutrino background experiments. In particular, AmBe sources are used to calibrate neutron tagging by selecting the 4438 keV γ-ray signal, which is simultaneously emitted with a neutron signal. Therefore, analyzing the neutron and γ-ray emission properties of AmBe sources is crucial. In this study, we used the theoretical shape of a neutron energy spectrum, which was divided into three parts, to develop models of the energy spectrum and verify the results using experimental data. We used an AmBe source to measure the energy spectra of simultaneously emitted neutrons and γ-rays and determine the emission ratio of the neutrons with and without γ-ray emission. The measured spectrum was consistent with that obtained from the simulated result, whereas the measured emission ratio was significantly different from the corresponding simulated result. Here, we also discuss the feasibility of determining the neutron emission rates from the spectra divided into three parts.

Reversible capacitive Frisch grid TlBr detectors

A reversible capacitive Frisch grid detector was fabricated using a thallium bromide (TlBr) crystal with a symmetrical electrode design. The device operates by switching the polarity of the applied voltage, which is necessary for a stable TlBr detector operation. A 2 mm × 2 mm × 5 mm bar-shaped TlBr crystal was used to construct the detector, which exhibited an (full width at half maximum) energy resolution of 1.9% for 662 keV γ-rays measured using a depth correction method at RT. The TlBr detector also showed a stable operation for 8 h of with hourly bias switching.

Measurement of the non-linearity in the [formula omitted]-ray response of the GAGG:Ce inorganic scintillator

A characteristic of every inorganic scintillator crystal is its light yield, i.e., the amount of emitted scintillation photons per unit of energy deposited in the crystal. Light yield is known to be usually non-linear with energy, which impacts the spectroscopic properties of the scintillator.Cerium-doped gadolinium–aluminium–gallium garnet (GAGG:Ce) is a recently developed scintillator with several interesting properties, which make it very promising for space-based γ-ray detectors, such as in the HERMES nanosatellite mission. In this paper we report an accurate measurement of the GAGG:Ce non-linearity in the 20–662 keV γ-ray energy interval, using a setup composed of three samples of GAGG:Ce crystals read out by Silicon Drift Detectors (SDDs).

Appropriateness of HSE06 exchange-correlation energies for post transition metal sesquioxides Ga2O3 and In2O3: Peculiarities in electronic states, momentum densities and thermoluminescence

Compton scattering measurements using 59.54 keV γ-rays have been reported for sesquioxides Ga2O3 and In2O3. To precisely compare the experimental and theoretical momentum densities, different exchange and correlation potentials within density functional theory and its hybridisation with Hartree-Fock (PBESOL0 and HSE06) have been considered. χ2 fitting analysis depicts HSE06 as a better choice for both sesquioxides. Present band structures, density of states and UV–vis measurements unambiguously support the use of HSE06 for such oxides and resolves issues related to appropriateness of exchange and correlation potentials. Higher covalent character in Ga2O3 than In2O3 using Mulliken's population is well explained by equal-valence-electron-density scaled CPs. Most prominent and firstly reported features in band structures of In2O3 are presence of parabolic trapping centres at Γ, H and N points with three direct band gaps of similar energy (3.37 eV), which may lead to its higher luminescence properties including potential applications in thermoluminescence dosimeters.

Monte Carlo simulation and study of REE/PET composites with wide γ-ray protection

In this paper, rare earth element (REE)/polyester composites were designed with lanthanum oxide, gadolinium oxide, and lutetium oxide as ray shielding agents, and polyethylene terephthalate (PET) as the base. Monte Carlo simulation was carried out using FLUKA software. We found that the radiation protection performance of the composite is affected by the type and amount of REE; a higher amount of REE equated to a better radiation protection performance of the composite. When the thickness of the composite and total thickness of the REE is constant, the number of superimposed layers inside the composite does not affect its shielding performance. Compared with a single-type REE/PET composite, a mixed-type REE/PET composite has a wider range of γ-ray absorption and better radiation protection performance. When the mass ratio of PET to REE is 2:8 and different types of REE are mixed with equal mass, several 0.2 cm-thick mixed-type REE/PET composites can shield >70% of 60 and 80 KeV γ-rays.

Hybrid SiC Pixel Detector for Charged-Particle Beam Monitor

We report on the hybrid SiC pixel detector for charged-particle beam monitors in high-energy physics experiments. To demonstrate comparable performances of the state-of-the-art Si pixel detectors, SiC pixel sensors with a die size of 25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were fabricated based on the p-n diode structure. We combined 12 × 12 diodes of a pixel size of 160 μm and 270 μm pitch with the dedicated readout ASIC by In/Au stud-bump technology. The front-end chip was designed in 0.35 μm CMOS technology, with consideration of a hybrid configuration. Each pixel circuit consists of a charge-sensitive amplifier and band-pass filter, optimized for the SiC sensor. The low noise performance achieved an equivalent noise charge of 55 ± 5e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–</sup> (rms). The spectrum of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">241</sup> Am shows an energy resolution of 1.72 keV (FWHM) at 17.8 keV γ-rays at room temperature. The obtained image with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Sr is a proof of a single MIP detection capability with all pixels. Those results prospect a future application of the SiC pixel sensors to high-intensity proton extinction monitors in the COMET muon experiment at Japan Proton Accelerator Research Complex.

A SiPM-based dual and triple coincidence system for positron annihilation lifetime measurement

Positron annihilation lifetime (PAL) spectroscopy is a powerful non-destructive method to study defects in materials. Silicon photomultipliers (SiPMs) have emerged as promising photodetector alternatives for PAL systems. However, further research is needed to fully optimize SiPM arrays for PAL applications. In this study, a dual and triple coincidence system has been developed based on four 1 × 4 SiPM arrays with resistor-chain readout, and initial results of PAL measurement have been obtained. A pixel-by-pixel time shift correction method was proposed and successfully applied using triple γ coincidence for summing 128 PAL spectra in one measurement. The system provides position, timing, and energy information for both 1275 and 511 keV γ-rays. The use of SiPM arrays and the pixel-by-pixel time shift correction method have enabled precise and reliable measurements of PALs in single-crystal silicon and yttria-stabilized zirconia samples. The developed SiPM-array-based PAL system also offers a technical solution to measure angular correlations of positron annihilation radiation, with the potential for further improvements.

Evaluation of a resistor-chain-based SiPM detector for positron annihilation lifetime measurement

Silicon photomultipliers (SiPMs) have great potential to replace photomultiplier tubes (PMTs) and exceed their performance in positron annihilation parameter-measurement systems. However, due to the limited active area of a single SiPM, it only covers a small γ-ray emission acceptance range and provides position information over a very small region. Using a SiPM array is a good way to overcome these problems. In this study, a resistor-chain-based SiPM detector was designed and evaluated for positron annihilation lifetime (PAL) measurements. This detector uses a 1 × 4 scintillator array, a 1 × 4 SiPM array, and a resistor-chain readout circuit to obtain position, energy, and timing information about 1275 and 511 keV γ-rays, with the readout pulses serving as both the position, energy, and timing signals. A comprehensive evaluation was conducted to assess the detector in terms of position profile, energy resolution, and time resolution. The position profiles showed that all the crystal elements in the lutetium fine silicate scintillator array were clearly resolved. The detector had an energy resolution of 11.3±0.9% and a time resolution of 198±9 ps. A total of 32 PAL spectra were obtained using two SiPM array detectors. The PAL in yttria-stabilized zirconia (YSZ) sample was accurately verified using the summed PAL spectrum. The developed SiPM detector provides good performance for PAL measurements and could be used to build a high-performance PAL spectrometer.