Γ-ray Energy Research Articles

Pseudo-redshifts of Gamma-Ray Bursts Derived from the L–T–E Correlation

The X-ray afterglow of many gamma-ray bursts (GRBs) exhibits a plateau phase before the normal power-law decay stage, which may be related to continued activities of the central engine. Tang et al. collected 174 such GRBs and confirmed the so-called L–T–E correlation which involves three key parameters, i.e., the isotropic γ-ray energy E γ,iso of the prompt phase, the end time T a of the plateau phase, and the corresponding X-ray luminosity L X. In this study, the L–T–E correlation is confirmed and updated as with a large sample consisting of 210 plateau GRBs with known redshifts. The tight correlation is then applied to derive the pseudo-redshift of other 130 plateau GRBs whose redshifts are not directly measured. Statistical analysis is also carried out on this pseudo-redshift sample.

Shock Breakout from Stellar Envelopes: The Relativistic Limit

We calculate the observed luminosity and spectrum following the emergence of a relativistic shock wave from a stellar edge. Shock waves propagating at 0.6 < Γsh β sh, where Γsh is the shock Lorentz factor, and β sh is its associated reduced velocity, heat the stellar envelope to temperatures exceeding ∼50 keV, allowing for a vigorous production of electron and positron pairs. Pairs significantly increase the electron-scattering optical depth and regulate the temperature through photon generation, producing distinct observational signatures in the escaping emission. Assuming Wien equilibrium, we find analytic expressions for the temperature and pair density profiles in the envelope immediately after shock passage, and compute the emission during the expansion phase. Our analysis shows that, in pair-loaded regions, photons are produced at a roughly uniform rest-frame energy of ∼200 keV, and reinforce previous estimates that the shock breakout signal will be detected as a short burst of energetic γ-ray photons, followed by a longer phase of X-ray emission. We test our model on a sample of low-luminosity gamma-ray bursts using a closure relation between the γ-ray burst duration, the radiation temperature, and the γ-ray isotropic equivalent energy, and find that some of the events are consistent with the relativistic shock breakout model. Finally, we apply our results to explosions in white dwarfs and neutron stars, and find that typical type Ia supernovae emit ∼1041 erg in the form of ∼1 MeV photons.

Nuclear Data Sheets for A=201

Evaluated nuclear structure and decay data for all nuclei with mass number A=201 (201Os, 201Ir, 201Pt, 201Au, 201Hg, 201Tl, 201Pb, 201Bi, 201Po, 201At, 201Rn, 201Fr, 201Ra) are presented. All available experimental data are compiled and evaluated, and best values for level and γ-ray energies, quantum numbers, lifetimes, γ-ray intensities and transition probabilities, as well as other nuclear properties, are recommended. Inconsistencies and discrepancies that exist in the literature are discussed. A number of computer codes (https://www-nds.iaea.org/public/ensdf_pgm/index.htm) developed by members of the NSDD network were used during the evaluation process. For example, the reported absolute γ-ray emission probabilities and their uncertainties in various decay data sets were determined using the GABS code. This work supersedes the earlier evaluation by F.G. Kondev (2007Ko06), published in Nuclear Data Sheets 108, 365 (2007).

Radiation shielding characterization of 83Bi209, 74W184, 50Sn119, ZnS, and CaCO3 using the modified Klein-Nishina formula

Radiation has many beneficial applications, particularly in healthcare and medicine. However, due to its hazards and adverse effects on human health, it is important to investigate materials for radiation shielding and protection purposes. In the present work, the electronic cross-sections, atomic cross-section, transfer cross-sections, Compton mass attenuation coefficients, and mass-energy transfer coefficients of 83Bi209, 74W184, 50Sn119, ZnS, and CaCO3 have been investigated using γ-ray energies ranging from 0.5 MeV to 18 MeV, by application of the Klein-Nishina formula. The results show that the electronic, atomic, and energy transfer cross-sections decrease with increasing γ-ray energy. The mass attenuation coefficients were observed to increase as the Z/A ratio increased. The mass energy-transfer coefficients decreased with an increasing Z/A ratio The Z/A ratio is an essential characteristic of a shielding material because it affects the scatter and absorption of γ-ray energy after a collision with an atom. The materials are found to be very suitable for radiation shielding and protection purpose. The investigated elements and compounds can also be used as lead alternative materials, to avoid environmental toxicity.

Spectral distribution and flux of [formula omitted]-ray beams produced through Compton scattering of unsynchronized laser and electron beams

Intense, quasi-monochromatic, polarized γ-ray beams with high and tunable energy produced by Compton scattering of laser photons against relativistic electrons are used for fundamental studies and applications. Following a series of photoneutron cross section measurements in the Giant Dipole Resonance (GDR) energy region performed at the NewSUBARU synchrotron radiation facility, we have developed the eliLaBr Monte Carlo simulation code for characterization of the scattered γ-ray photon beams. The code is implemented using Geant4 and is available on the GitHub repository (https://github.com/dan-mihai-filipescu/eliLaBr). Here we report the validation of the eliLaBr code on NewSUBARU LCS γ-ray beam flux and spectral distribution data and two applications performed with it for asymmetric transverse emittance profiles electron beams, characteristic for synchrotrons.The first application is based on a systematic investigation of transverse collimator offsets relative to the laser and electron beam axis. We show that the maximum energy of the LCS γ-ray beam is altered by vertical collimator offsets, where the edge shifts towards lower energies with the increase in the offset.Secondly, using the eliLaBr code, we investigate the effect of the laser polarization plane orientation on the properties of the LCS γ-ray beams produced with asymmetric emittance electron beams. We show that:1. The use of vertically polarized lasers contributes to the preservation of the LCS γ-ray beam maximum energy edge by increasing the precision in the vertical collimator alignment.2. Under identical conditions for the electron and laser beams phase-space distributions, the energy spectrum of the scattered LCS γ-ray beam changes with the laser beam polarization plane orientation. More precisely, the use of vertically polarized laser beams slightly deteriorates the LCS γ-ray beam energy resolution.

Study of timing performance parameters for a SiPM-based digital positron annihilation lifetime spectrometer

Abstract Positron annihilation lifetime spectroscopy (PALS) is a popular method for studying defects in materials. With the development of fast digital oscilloscopes and digitizers, the conventional analog positron annihilation lifetime (PAL) spectrometer is being replaced by a digital PAL spectrometer. Recently, newly conducted research has developed a PAL spectrometer using a silicon photomultiplier (SiPM) instead of a photomultiplier tube (PMT). Timing resolution of PAL spectrometer needs to be improved to identify the lifetimes of positrons. Many parameters affect the timing performance of a SiPM-based digital PAL spectrometer: bias voltage, pulse smoothing, and the constant fraction value of digital constant fraction discrimination (dCFD). Timing resolution depends on the radiation energy, but only a few studies have considered the energy difference of 1274 keV and 511 keV. In this study, we optimized the timing performance parameters of the SiPM-based digital PAL spectrometer by conducting the timing resolution measurements using two γ-ray sources (22Na and 60Co). With a 32 V bias voltage, 5th degree polynomial fitting method, and optimal constant fraction value, we optimized the timing resolution of our SiPM-based digital PAL spectrometer. Furthermore, the optimal constant fraction value depended on the γ-ray energy and we verified it by timing resolution measurement using 207Bi. We studied the reason why performance parameters have optimal conditions and the optimal constant fraction value varies depending on the γ-ray energy. With optimized performance parameters, we measured the lifetime spectrum of pure silicon to confirm the SiPM-based digital PAL spectrometer. The timing resolution function of the SiPM-based digital PAL spectrometer was 185.6 ps.

Characterization of the thickness of dead layer and cold finger for portable HPGe γ-spectrometer

The internal structure of the HPGe γ-spectrometer will change with increasing use time, which will significantly impact the accuracy of the modelling simulation results. In this paper, the characterization method of the structural parameters of the HPGe γ-spectrometer is investigated, and the characterization results are presented. Experimental measurements and Monte Carlo simulations are performed at four different positions using six radioactive point sources covering low, medium, and high energies of γ-rays, respectively. The thickness of the dead layer on the front and lateral surface and cold finger on the front and lateral surface are adjusted sequentially according to the characterization algorithm. The thickness of the dead layer on the front surface is corrected to 0.21 cm, and the dead layer on the lateral surface is corrected to 0.08 cm. The thickness of the cold finger on the front surface and lateral surface does not change. The maximum relative deviation of the Monte Carlo simulation results from the experimental results was reduced from 72.7% before correction to 4.3%.

The steady-state multi-TeV diffuse γ-ray emission predicted with galprop and prospects for the Cherenkov Telescope Array

ABSTRACT Cosmic rays (CRs) interact with the diffuse gas, radiation, and magnetic fields in the interstellar medium (ISM) to produce electromagnetic emissions that are a significant component of the all-sky flux across a broad wavelength range. The Fermi–Large Area Telescope (LAT) has measured these emissions at GeV γ-ray energies with high statistics. Meanwhile, the high-energy stereoscopic system (H.E.S.S.) telescope array has observed large-scale Galactic diffuse emission in the TeV γ-ray energy range. The emissions observed at GeV and TeV energies are connected by the common origin of the CR particles injected by the sources, but the energy dependence of the mixture from the general ISM (true ‘diffuse’), those emanating from the relatively nearby interstellar space about the sources, and the sources themselves, is not well understood. In this paper, we investigate predictions of the broad-band emissions using the galprop code over a grid of steady-state 3D models that include variations over CR sources, and other ISM target distributions. We compare, in particular, the model predictions in the very-high energy ( VHE; ≳100 GeV) γ-ray range with the H.E.S.S. Galactic plane survey (HGPS) after carefully subtracting emission from catalogued γ-ray sources. Accounting for the unresolved source contribution, and the systematic uncertainty of the HGPS, we find that the galprop model predictions agree with lower estimates for the HGPS source-subtracted diffuse flux. We discuss the implications of the modelling results for interpretation of data from the next generation Cherenkov Telescope Array (CTA).

Gamma-ray spectral variability of HBL 1ES 1959+650 during MJD 57400–58000 and its consequence on leptonic blazar emission model

ABSTRACT 1ES 1959+650, a high-energy peaked BL Lac object (HBL) with redshift z = 0.047, is known to exhibit flux and spectral variability in different energy bands. In this work, we primarily considered the simultaneous Fermi-LAT and Swift-XRT data of 1ES 1959+650 to study the flux and spectral variability in the energy ranges (0.1–300 GeV) and (0.6–10 keV), respectively. Using the Fermi-LAT light curve, a stretch of quiescent state and three high flux states of the source were identified. The flux and the spectral variability were studied using flare profiles and flux-index loops. In the γ-ray energies, 1ES 1959+650 clearly showed the evolution ‘softer-when-brighter’ whereas in the X-rays it showed the trend ‘harder-when-brighter’. 1ES 1959+650 also showed quick changes in spectral shape in the γ-ray band when the γ-ray flux was changing during the flares. The spectral energy distributions (SEDs) of the source were constructed using simultaneous data from Fermi-LAT, Swift-XRT, Swift-UVOT during its evolution. The TeV data from TACTIC imaging telescope were also used to construct the SED in the quiescent state. The spectral modelling of the SEDs revealed that due to the spectral variability of 1ES 1959+650, the standard leptonic one zone model cannot be used to explain the emission from this source. Instead a two zone leptonic model is needed to explain the observed SEDs from this blazar.

Radiation shielding properties of Cd-Bi-Pb-Zn-borate glasses: influence of Bi2O3 activation

We report the detail characterizations and γ-radiation protecting characteristics of some new types of cadmium (Cd)-bismuth (Bi)-lead (Pb)-zinc (Zn)-borate glasses of the form (70-x)B2O3-10ZnO-10PbO-10CdO-xBi2O3 (with x = 0 to 20 mol%) synthesized via melt-quenching process. The influence of various Bi2O3 contents on the γ-radiation shielding traits of the obtained glass samples was evaluated by exposing them at different γ-ray energies (0.356, 0.662, 1.173, and 1.33 MeV) which were recorded by the NaI detector. XRD analyses of the as-quenched specimens showed their glassy phase. A comparison between theoretically computed (Phy-X and XCOM software) and experimentally measured various shielding parameters of the glass samples were performed. Irrespective of the Bi2O3 contents, the values of the mass attenuation coefficient, effective atomic number and effective electron density of the prepared glass samples were reduced with the increase of γ-ray energies. Furthermore, the theoretically calculated values of all the shielding parameters were agreed well with the measured ones. Regardless of the γ-ray energy exposures, the shielding capacity of the studied glasses was improved with the increase of Bi2O3 doping contents. The proposed glass compositions were asserted to be useful for the γ-ray absorber applications.

A deep spectromorphological study of the γ-ray emission surrounding the young massive stellar cluster Westerlund 1

Context. Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they are increasingly considered as being responsible for a significant fraction of cosmic rays (CRs) that are accelerated within the Milky Way. Westerlund 1, the most massive known young stellar cluster in our Galaxy, is a prime candidate for studying this hypothesis. While the very-high-energy γ-ray source HESS J1646−458 has been detected in the vicinity of Westerlund 1 in the past, its association could not be firmly identified. Aims. We aim to identify the physical processes responsible for the γ-ray emission around Westerlund 1 and thus to understand the role of massive stellar clusters in the acceleration of Galactic CRs better. Methods. Using 164 h of data recorded with the High Energy Stereoscopic System (H.E.S.S.), we carried out a deep spectromorphological study of the γ-ray emission of HESS J1646−458. We furthermore employed H I and CO observations of the region to infer the presence of gas that could serve as target material for interactions of accelerated CRs. Results. We detected large-scale (∼2° diameter) γ-ray emission with a complex morphology, exhibiting a shell-like structure and showing no significant variation with γ-ray energy. The combined energy spectrum of the emission extends to several tens of TeV, and it is uniform across the entire source region. We did not find a clear correlation of the γ-ray emission with gas clouds as identified through H I and CO observations. Conclusions. We conclude that, of the known objects within the region, only Westerlund 1 can explain the majority of the γ-ray emission. Several CR acceleration sites and mechanisms are conceivable and discussed in detail. While it seems clear that Westerlund 1 acts as a powerful particle accelerator, no firm conclusions on the contribution of massive stellar clusters to the flux of Galactic CRs in general can be drawn at this point.

Diffuse non-thermal emission in the disks of the Magellanic Clouds

Context. The Magellanic Clouds, two dwarf galaxy companions to the Milky Way, are among the Fermi Large Area Telescope (LAT) brightest γ-ray sources. Aims. We present comprehensive modeling of the non-thermal electromagnetic and neutrino emission in both Clouds. Methods. We self-consistently model the radio and γ-ray spectral energy distribution from their disks based on recently published Murchison Widefield Array and Fermi/LAT data. All relevant radiative processes involving relativistic and thermal electrons (synchrotron, Compton scattering, and bremsstrahlung) and relativistic protons (neutral pion decay following interaction with thermal protons) are considered, using exact emission formulae. Results. Joint spectral analyses indicate that radio emission in the Clouds has both primary and secondary electron synchrotron and thermal bremsstrahlung origin, whereas γ rays originate mostly from π0 decay with some contributions from relativistic bremsstrahlung and Comptonized starlight. The proton spectra in both galaxies are modeled as power laws in energy with similar spectral indices, ~2.4, and energy densities, ~1 eV cm−3. The predicted 0.1–10 GeV neutrino flux is too low for detection by current and upcoming experiments. Conclusions. We confirm earlier suggestions of a largely hadronic origin of the γ-ray emission in both Magellanic Clouds.

Primary standardization of 212Pb activity by liquid scintillation counting

An activity standard for 212Pb in equilibrium with its progeny was realized, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. A Monte Carlo-based approach to estimating uncertainties due to nuclear decay data (branching ratios, beta endpoint energies, γ-ray energies, and conversion coefficients for 212Pb and 208Tl) led to combined standard uncertainties ≤ 0.20 %. Confirmatory primary measurements were made by LS efficiency tracing with tritium and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting. The standard is discussed in relation to current approaches to 212Pb activity calibration. In particular, potential biases encountered when using inappropriate radionuclide calibrator settings are discussed.

Measurement of [formula omitted] and [formula omitted] binding energy in Au+Au collisions at [formula omitted] = 3 GeV

Measurements of mass and Λ binding energy of Λ4H and Λ4He in Au+Au collisions at sNN=3 GeV are presented, with an aim to address the charge symmetry breaking (CSB) problem in hypernuclei systems with atomic number A = 4. The Λ binding energies are measured to be 2.22±0.06(stat.)±0.14(syst.) MeV and 2.38±0.13(stat.)±0.12(syst.) MeV for Λ4H and Λ4He, respectively. The measured Λ binding-energy difference is 0.16±0.14(stat.)±0.10(syst.) MeV for ground states. Combined with the γ-ray transition energies, the binding-energy difference for excited states is −0.16±0.14(stat.)±0.10(syst.) MeV, which is negative and comparable to the value of the ground states within uncertainties. These new measurements on the Λ binding-energy difference in A = 4 hypernuclei systems are consistent with the theoretical calculations that result in ΔBΛ4(1exc+)≈−ΔBΛ4(0g.s.+)<0 and present a new method for the study of CSB effect using relativistic heavy-ion collisions.

Radiation attenuation capacity improvement of various oxides via high density polyethylene composite reinforcement

This paper reports the improved gamma radiation attenuation ability of six composite shields prepared using high density polyethylene (HDP) reinforced Al2O3, Fe2O3, and PbO. The radioactive source 226Ra was used at different γ-ray energies (0.295, 0.352, 0.609, 1.12, and 1.747 MeV) and the transmitted γ-radiation from the studied shields was detected via a NaI(Tl) detector. The proposed shields' μ, MFP, HVL, TF, RPE, and dPb values were determined as a function of γ-ray energy. The experimental results were compared with those calculated using the XMuDat computer program. The measured values of all parameters were consistent with the theoretical results. It was demonstrated that the gamma radiation attenuation capacity of Al2O3, Fe2O3, and PbO can be significantly enhanced via HDP reinforcement.

Characterisation of a 1[formula omitted] LaBr2.85Cl0.15:Ce crystal for [formula omitted]-rays up to 4.4 MeV

This communication reports about complete characterisation of a small volume 1′′×1′′ cylindrical LaBr2.85 Cl0.15:Ce crystal supplied by Scionix Inc. for γ-rays up to 4.4 MeV. The various properties of the crystal studied, are, linearity of response for γ-rays, energy resolution up to 4.4 MeV, timing resolutions, quantification of internal activity, and full energy detection efficiencies for γ-rays from 276 to 4439 keV. Monte Carlo simulation toolkit GEANT4 was used to carry out realistic simulations of the detector’s response for γ-rays. Experimental γ-ray energy spectrum was reproduced in the simulations to estimate the full energy detection efficiency for γ-rays and compared with the measured value. We have obtained energy resolution of ∼3.8% at 662 keV using 2′′ ET-9266B PMT biased at −800 V with the energy signal drawn from the 8th dynode. Timing resolutions of 422 and 364 ps were obtained using 2′′ ET-9807B PMT for 22Na and 60Co, respectively. To the best of our knowledge, this is the first report on the performance of the newly manufactured and marketed LBC crystal. We do not find any significant difference in the performance of LBC from that of a standard Lanthanum Bromide (Ce activated) crystal of similar volume.

Algorithms of pulse shape analysis for Gammasphere under high count rate conditions

The implementation of digital electronics for the multi-detector Gammasphere array has provided an opportunity to perform experiments which exceed the technical capabilities of its analog counterpart. The pulse shape analysis of HPGe detectors is presented for the purpose of determining the γ-ray energy under high-counting rates and short integration times with the aim of improving the data throughput. A revised trapezoidal algorithm is delineated which is able to determine the γ-ray energies during the offline analysis without being constrained by predetermined parameters. The performance of this algorithm is discussed, and compared with that of the analog system. The measured energy resolution meets expectations for operations with high-counting rates and short integration times.

Formula omitted]-ray energy spectrum response tailing in CdZnTe detector

Affected by the characteristics of carrier transport, the γ-ray energy spectrum of the cadmium zinc telluride (CZT) detector usually has a low-energy tail phenomenon The traditional γ -ray energy spectrum response simulation model is mainly aimed at detectors with a uniform internal electric field, not suitable for non-uniform internal electric fields, and cannot accurately characterize the low-energy tailing phenomenon of the γ -ray energy spectrum of CZT detectors. In this study, for the quasi-hemispherical and coplanar-grid CZT detectors, the Geant4 program was used to establish the energy deposition model, and the γ-ray energy deposition and the carrier distribution in the two detectors were obtained. On this basis, the finite element analysis method was used to construct the internal electric field of the two detectors, and the charge collection efficiency model is established according to the transport law of carriers in the detectors. Finally, the above model was used to simulate the γ energy spectrum response of the four nuclides 241Am, 133Ba, 137Cs, and 60Co, and the simulation results were verified through experiments. The results show that the method in this paper can accurately describe the low-energy tail of the γ-ray energy spectrum of the two CZT detectors, and the obtained simulated γ-ray energy spectrum is basically consistent with the full-spectrum characteristics of the measured energy spectrum.

Assessment of γ-radiation shielding behavior of some mixed nature clays

Recently, clay materials have earned prominence as potential materials in the γ-radiation shielding and protection areas compared to other conventional materials. From this point, the present study is devoted to preparing a new composite of two types of clays, based on bentonite clay, as a natural, plentiful, and low-cost matrix. The chemical composition of prepared samples was indicated by Energy dispersive x-ray analysis (EDX). Morphology of clay samples was examined using scanning electron microscopy (SEM). The SEM images showed that the homogeneity and porosity of a cross section of samples. Measurements of the γ-ray shielding performance was analyzed and determined at numerous γ-ray photon energies emitted from five point sources of γ-rays using NaI(Tl) scintillation detector. Thus, the linear attenuation coefficient (LAC) was calculated by obtaining area under each peak of the energy spectrum observed from Genie 2000 software in the presence and absence of the clay sample. The experimental results obtained were compared theoretically with XCOM software. The comparison was examined the validity of experimental results. The other dependent radiation shielding parameters on the LAC such as a half attenuator layer (HAL), mean free path (MFP), Transmission factor (TF), and the radiation absorption ratio (RAR) were measured. It was confirmed that the γ-ray shielding properties were enhanced by mixing two types of clay comparing with the individual one. Clay materials would be good applicants for use in construction and civil engineering, as well as in the fabrication of building materials used in medical and nuclear establishments.

Bright attosecond polarized [formula omitted]-ray emission from the interaction of an intense laser pulse with non-uniform near-critical-density plasma

We study a scheme for the generation of attosecond (as) polarized γ-rays in the interaction of an intense laser with non-uniform near-critical-density (NCD) plasma. Longitudinal and transverse non-uniform plasma channels are used to enhance the efficiency of the γ-ray emission. As the laser pulse propagates in a non-uniform plasma channel, a large number of electrons are first trapped and accelerated to GeV energies and then collide head-on with a laser pulse reflected from a convex plasma mirror; then, γ-rays with energies up to several GeV are emitted. For the longitudinal non-uniform plasma, the γ-ray cutoff energy reaches 2.3 GeV, while it reaches approximately 2 GeV for the transverse non-uniform plasma and only 1.2 GeV for the uniform case. We found that by counting the photons with energy above 1 GeV, a sub-femtosecond γ-ray with a duration of approximately 760 as and divergence angle of 6° is generated in the longitudinal non-uniform plasma. This γ-ray has an unprecedented peak brightness of 5.7×1026photons/(s mm2mrad2 0.1%BW) (at 1 GeV). Based on the simulation data, we theoretically calculated the γ photon polarization probability and polarization degree. The results show that the photons are more likely to be emitted into a polarization state that is parallel to the polarization of the background field, and thus possess a positive polarization degree of approximately 0.6.