MeV Γ-rays Research Articles

First Constraints on the Photon Coupling of Axionlike Particles from Multimessenger Studies of the Neutron Star Merger GW170817.

We use multimessenger observations of the neutron star merger event GW170817 to derive new constraints on axionlike particles (ALPs) coupling to photons. ALPs are produced via Primakoff and photon coalescence processes in the merger, escape the remnant, and decay back into two photons, giving rise to a photon signal approximately along the line of sight to the merger. We analyze the spectral and temporal information of the ALP-induced photon signal and use the Fermi Large Area Telescope (Fermi-LAT) observations of GW170817 to derive our new ALP constraints. We also show the improved prospects with future MeV γ-ray missions, taking the spectral and temporal coverage of Fermi-LAT as an example.

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.

Measurement of proton induced absolute production cross-section of 6.13, 6.92 and 7.12 MeV γ-rays from 16O(p,p ′γ )16O reaction

In this article, we report the absolute production cross-section of 6.13, 6.92 and 7.12 MeV γ-rays from the 16O(p,p ′γ )16O reaction for incident proton energy range of 8-16 MeV. Angular distributions of the three γ-rays have been measured for seven angles at 9 MeV proton energy. A detailed phenomenological optical model potential (OMP) was set up to analyse the cross-section data. The OMP parameters were optimised using elastic, polarization and total reaction data available in the literature for protons and neutrons. Low-lying states of 16O were coupled, the optical potential was deformed using deformation parameters, and several resonances were included in the calculations to account for the nuclear structure effects. The potentials so generated have been used to calculate the differential and total cross sections for both 16O(p,p ′ )16O and 16O(p,p ′γ )16O reactions. Our calculated cross-sections are in fairly good agreement with our measured data for 6.13, 6.92 and 7.12 MeV γ-rays. However, there still exist discrepancies in reproduction of the finer details of the cross sections. The comparisons of the calculations with the data bring forth the rather complex roles of channel couplings, resonances in the p+16O system and target deformation in the variation of the cross sections with projectile energy. The increased contribution of nuclear structure effects in light mass nuclei, leads to an apparent loss of predictive power of the theoretical calculation, as we approach the low-energy region of less than 10 MeV projectile energy.

Lineshape response of plastic scintillator to pair production of 4.44 MeV [formula omitted]’s

We measure the distribution of energy deposited in a 40 × 88 mm plastic scintillator by e+e− pair production of 4.44 MeV γ-rays. We observe the double-escape peak of 3.42 MeV from pair production by tagging 511 keV annihilation radiation in two high-Z scintillators. The source is a standard commercial neutron source using α-emitting 241Am encapsulated with 9Be, which has a reaction branch feeding the first Iπ=2+ state of 12C making the 4.44 MeV γ-rays. We demonstrate the extraction of the double-escape peak from the large neutron-produced backgound, and explore some of the features and difficulties of this technique with our apparatus.

Design and construction of a 9 MeV [formula omitted]-ray source based on capture of moderated plutonium–beryllium neutrons in nickel

We have designed and constructed a high-energy γ-ray source for detector characterisation and calibration. The source is a composite type based on a plutonium–beryllium neutron emitter embedded in a paraffin moderator, which is homogeneously mixed with nickel powder. The 9 MeV γ-ray source produces approximately 450 photons per second in 4π when 2.2×105 neutrons per second are emitted, corresponding to a surface flux of 9 MeV γ-rays of approximately 2.5×10−6 cm−2 per emitted neutron. Here we discuss the properties and design of this source, including the characterisation of homogeneity and high-energy γ-ray emission spectra.

Thick-target yield of [formula omitted][formula omitted] ray from the resonant reaction [formula omitted]Li[formula omitted]Be at E[formula omitted] = [formula omitted

High energy γ-ray plays an important role in the study of the nuclear industry and nuclear physics. (p,γ) resonant reaction is a classic way to produce quasi-monochromatic γ-ray. The determination of (p,γ) yield is an important prerequisite for using this γ-ray source to carry out subsequent work. In this work, the 7Li(p,γ)8Be resonant reaction at Ep = 441 keV is utilized to produce 17.6 MeV γ-ray using the 2×1.7 MV tandem accelerator at CIAE. The full yield curve is measured for the first time. The maximum thick-target-yield of 17.6 MeV γ-ray is determined to be (3.2 ± 0.2)×10−9γ/p. This would lead to the γ-ray intensity of 2×108 /s when using 10 mA proton beam which has been typically available to date. This intensity is comparable to the one from the laser-Compton scattering facilities in operation. Thus can be used for study of photonuclear reactions.

Gamma-ray light curves and spectra of classical novae

ABSTRACT The nucleosynthesis in classical novae, in particular that of radioactive isotopes, is directly measurable by its γ-ray signature. Despite decades of observations, MeV γ-rays from novae have never been detected – neither individually at the time of the explosion, nor as a result of radioactive decay, nor the diffuse Galactic emission from the nova population. Thanks to recent developments in modelling of instrumental background for MeV telescopes such as INTEGRAL/SPI and Fermi/GBM, the prospects to finally detect these elusive transients are greatly enhanced. This demands for updated and refined models of γ-ray spectra and light curves of classical novae. In this work, we develop numerical models of nova explosions using sub- and near-Chandrasekhar CO white dwarfs as the progenitor. We study the parameter dependence of the explosions, their thermodynamics and energetics, as well as their chemical abundance patterns. We use a Monte Carlo radiative transfer code to compute γ-ray light curves and spectra, with a focus on the early time evolution. We compare our results to previous studies and find that the expected 511-keV-line flash at the time of the explosion is heavily suppressed, showing a maximum flux of only $10^{-9}\, \mathrm{ph\, cm^{-2}\, s^{-1}}$ and thus making it at least one million times fainter than estimated before. This finding would render it impossible for current MeV instruments to detect novae within the first day after the outburst. Nevertheless, our time-resolved spectra can be used for retrospective analyses of archival data, thereby improving the sensitivity of the instruments.

Measurement of the low energy 25Mg(p,γ)26Al resonances

The cosmic 1.809 MeV γ-ray emitted by the radioactive nucleus 26Al in the Galaxy is one of the key observation targets of the γ-ray astronomy. The 26Al is mainly produced by the 25Mg(p,γ)26Al reaction in the stellar Mg-Al reaction cycle. At the astrophysical relevant temperatures, the reaction rates of 25Mg(p,γ)26Al are dominated by several narrow resonances at low energy. This work reports a measurement of the low energy 25Mg(p,γ)26Al resonances at Jinping Underground Nuclear Astrophysics experimental facility (JUNA) in the China Jinping Underground Laboratory (CJPL).

Axion-like Particles from Nearby Type Ia Supernovae

Axion-like particles (ALPs) are a class of hypothetical pseudo-scalar particles and can be created in hot astrophysical plasma through the interaction between photons. I calculate the production of ALPs in type Ia supernovae. It is found that many ALPs lighter than a few MeV can be produced in type Ia supernovae. Once produced, heavy ALPs decay into photons during propagation in the interstellar space. I calculate the flux of the decay photons and find that it may be detected by future MeV γ-ray telescopes if a type Ia supernova explodes near the Solar System.

First result from the Jinping Underground Nuclear Astrophysics experiment JUNA: precise measurement of the 92 keV 25Mg(p, [formula omitted])26Al resonance

The 25Mg(p, γ)26Al reaction plays an important role in the study of cosmic 1.809 MeV γ-ray as a signature of ongoing nucleosynthesis in the Galaxy. At astrophysical temperature around 0.1 GK, the 25Mg(p, γ)26Al reaction rates are dominated by the 92 keV resonance capture process. We report a precise measurement of the 92 keV 25Mg(p, γ)26Al resonance in the day-one experiment at Jinping Underground Nuclear Astrophysics experiment (JUNA) facility in the China Jinping Underground Laboratory (CJPL). The resonance strength and ground state feeding factor are determined to be 3.8±0.3 ×10−10 eV and 0.66±0.04, respectively. The results are in agreement with those reported in the previous direct underground measurement within uncertainty, but with significantly reduced uncertainties. Consequently, we recommend new 25Mg(p, γ)26Al reaction rates which are by a factor of 2.4 larger than those adopted in REACLIB database at the temperature around 0.1 GK. The new results indicate higher production rates of 26gAl and the cosmic 1.809 MeV γ-ray. The implication of the new rates for the understanding of other astrophysical situations is also discussed.

Heavy axion-like particles and MeV decay photons from nearby type Ia supernovae

Abstract Axion-like particles (ALPs) are hypothetical bosons which may couple with photons. Since many ALPs can be emitted from hot and dense astrophysical plasma, nearby supernovae (SNe) are a possible probe into their properties, including the ALP mass ma and the coupling constant gaγ between ALPs and photons. I calculate the ALP emission from a type Ia SN (SN Ia) model with near-Chandrasekhar mass, finding that ALP luminosities from SNe Ia reach ∼1043(gaγ/10−10 GeV−1)2 erg s−1 if ma ≲ 1 MeV. Heavy ALPs emitted from SNe are unstable and decay into photons. I predict the time delay and the flux of decay photons that reach Earth from a nearby SN Ia, finding that the decay photons may provide a constraint on gaγ which is as stringent as the SN 1987A limit if an SN Ia is located 1 kpc away or closer and next-generation MeV γ-ray satellites observe it ∼1–10 yr after the explosion.

Formula omitted]-particle induced yield of 6.13 MeV [formula omitted]-rays in carbon

Results from a preliminary accelerator-based experiment conducted at the Harwell Tandem Van de Graaff generator to estimate the thick target integrated over angle yield of 6.129 MeV γ-rays from α-particles in the MeV range stopping in natural carbon are briefly outlined. The results should be useful in planning future detailed experiments to generate data for applications and also to benchmark thin target cross section evaluations. The estimated yields referred to a natural 13C abundance of 1.09 atom % at 5.597, 5.801, and 5.999 MeV in units of 6.129 MeV γ-rays per 108α-particles are: 1.04, 1.62 and 3.31, respectively. An indicative overall relative uncertainty at the 68 % confidence level is estimated to be about 6%, although we caution that, being undertaken only as a feasibility study, the checks and balances we would usually conduct were not performed.

First spatially resolved measurements of the D-3He α-particle source with the upgraded JET gamma-ray camera.

The Joint European Torus (JET) gamma-ray camera has been recently upgraded with the installation of new gamma-ray detectors, based on LaBr3(Ce) scintillation crystals, which add spectroscopic capability to the existing system allowing measurements with good energy resolution (5% at 0.622MeV), a dynamic range from hundreds of keV up to about 30MeV, and high counting rate capabilities of MCps. First gamma-ray measurements during the C38 campaign of the JET have been successfully carried out, in particular, in D-3He plasmas from three-ion ion cyclotron resonance heating experiments, where the detection of 16.4MeV γ-rays from D + 3He → γ + 5Li reactions with the gamma-ray camera upgrade allowed determining the spatial profile of alpha particles born in D + 3He fusion reactions.

Reckoning of nuclear radiation attenuation capabilities for binary GeO2-Tl2O, GeO2-Bi2O3, and ternary GeO2-Tl2O–Bi2O3 glasses utilizing pertinent theoretical and computational approaches

Abstract In this work, a total of eight thallium germanate, bismuth germanate, and bismuth thallium germanate glasses were explored for nuclear radiation shielding purposes. By employing the WinXCOM dependent Phy-X/PSD program, linear attenuation coefficient (μ) and mass attenuation coefficient (μ/ρ) values have been figured out within γ-ray energy range of 0.015–15 MeV and acquired μ/ρ quantities are in well accord with simulated Geant4 and Penelope codes μ/ρ results, accordingly. Some other relevant γ-ray attenuation parameters like effective atomic number (Zeff), effective electron density (Neff), half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP) were evaluated with the aid of Phy-X/PSD μ/ρ results. All μ/ρ, Zeff, Neff, HVL, TVL, and MFP parameters rely upon both samples' chemical composition and γ-ray energy. In place of GeO2, the inclusion of Tl2O and/or Bi2O3 in all selected samples demonstrates the enhanced γ-ray attenuation capacity with increasing Zeff and lower HVL, TVL, and MFP values. Besides, utilizing geometric progression (G‒P) fitting approach, within 0.015–15 MeV γ-ray energy range exposure buildup factors (EBFs) and energy absorption buildup factors (EABFs) have been estimated at discrete penetration depths (up to 40 mfp) and larger EBFs and EABFs are attained at higher energies with greater penetration depths. The ternary 16GeO2-62Tl2O–22Bi2O3 (mol%) glass, among all the tested samples, by owing comparatively larger μ, μ/ρ, and Zeff, lower HVL, TVL, MFP, EBFs, and EABFs, validate its' superior γ-ray attenuation ability as even HVL and MFP quantities of this sample are lower than some of the commercial shielding glasses, alloys, polymers, and concretes respective values when compared. Additionally, for all samples, neutron total cross-section (σT) values are derived within the neutron energy range of 10−8‒10 MeV by exerting Geant4 code. At 10−8 and 10 MeV neutron energies, the obtained ‘σT’ values are varied within 0.3589–0.4245 cm−1 and 0.13–0.1439 cm−1 ranges, respectively, for all studied glasses.

Evidence for a Coronal Shock Wave Origin for Relativistic Protons Producing Solar Gamma-Rays and Observed by Neutron Monitors at Earth

Abstract We study the solar eruptive event on 2017 September 10 that produced long-lasting >100 MeV γ-ray emission and a ground level enhancement (GLE72). The origin of the high-energy ions producing late-phase gamma-ray emission (LPGRE) is still an open question, but a possible explanation is proton acceleration at coronal shocks produced by coronal mass ejections. We examine a common shock acceleration origin for both the LPGRE and GLE72. The γ-ray emission observed by the Fermi-Large Area Telescope exhibits a weak impulsive phase, consistent with that observed in hard X-and γ-ray line flare emissions, and what appear to be two distinct stages of LPGRE. From a detailed modeling of the shock wave, we derive the 3D distribution and temporal evolution of the shock parameters, and we examine the shock wave magnetic connection with the visible solar disk. The evolution of shock parameters on field lines returning to the visible disk mirrors the two stages of LPGRE. We find good agreement between the time history of >100 MeV γ-rays and one produced by a basic shock acceleration model. The time history of shock parameters magnetically mapped to Earth agrees with the rates observed by the Fort Smith neutron monitor during the first hour of GLE72 if we include a 30% contribution of flare-accelerated protons during the first 10 minutes, having a release time following the time history of nuclear γ-rays. Our analysis provides compelling evidence for a common shock origin for protons producing the LPGRE and most of the particles observed in GLE72.

Shielding capabilities study of light-gray, pale-pink and orange-pink Zacatecan quarries against ionizing photons using EDXRF and XCOM code

In this work the shielding capacity of three quarries widely used in the construction industry in Mexico has been determined. The reported features include the mass interaction coefficients, the linear attenuation coefficients and the average value layers. The Energy Dispersed X-Ray Fluorescence (EDXRF) shows that an element such as oxygen (contained in Portland concrete and gypsum, but not in quarries), which alone is irrelevant to shield ionizing energies, may become relevant to explain the shielding capacity of materials. The total linear attenuation coefficients and the half value layers were calculated for photon energies related to the medical field. Our results show that light-gray, pale-pink and orange-pink Zacatecan quarries shield ionizing photons below 70 keV three times better that gypsum and that they shield even better than Portland concrete. The experimental photon transmission of 0.662 MeV γ-rays in terms of the thickness of the G1, G2 and G3 quarries, adjusts without significant differences to the provisions of the attenuation law.

Radiation Diagnostics of Pipelines and Equipment of Oil and Gas Production Complexes

An alert indicating the formation of salt deposits in the pipelines of oil and gas production complexes reduces the financial losses associated with the removal of these deposits and the loss of production. A method of taking into account the presence of the native radionuclide 232Th and its decay product 208Tl in the deposits is proposed for performing radiation diagnostics of pipelines. The appearance of the deposits is identified according to the 2.614 MeV γ-rays. The thickness of the deposits is determined according to the attenuation of the γ-rays from an external thorium dioxide source placed on the outer surface of a pipe. Calculations confirmed the presence of 1–2 mm thick deposits with probability 0.9 and a false positive rate of 0.01 in 1 h measurements with background 3 counts/sec. A 232Th-based external source with activity 105 and 106 Bq makes it possible to determine deposit thicknesses 2.5–3 and 1–2 mm, respectively, with measurement time 1 h and error about 15%.

Response of a lead-free borosilicate-glass microchannel plate to 14-MeV neutrons and γ-rays

In microchannel plate applications, such as in space telescopes, night-vision devices, or time-of-flight particle detection, reducing the sensitivity to signals from background sources, such as γ-rays, is beneficial for the system design and performance. The response of a single-stage lead-free borosilicate-glass microchannel plate to 14-MeV neutrons and γ-rays produced via (n, γ) reactions in surrounding structures was investigated at OMEGA. The average efficiency values for secondary electron production were found to be (5.1 ± 0.7) × 10−3 for 14-MeV neutrons and (4.9 ± 1.1) × 10−3 for ⟨1.5⟩-MeV γ-rays.

Hard X-ray Bremsstrahlung of relativistic Runaway Electrons in JET

One of the main requirements to the Disruption Mitigation System (DMS) in International Thermonuclear Experimental Reactor (ITER) is a reliable capability to avoid/suppress a detrimental runaway electron (RE) generation during disruptions. An understanding of the physics of RE is a key factor for design of ITER DMS with necessary properties on RE suppression. RE interacting with plasma particles and hitting the plasma-facing components (PFCs) produce a bremsstrahlung in MeV energy range (hard X-rays (HXR) and γ-rays) and photo-neutrons. Measurements of produced HXR/γ-rays and photo-neutrons provide detailed information on RE generation and serve as a main tool for runaway physics study in JET. This report presents recent progress in development of the JET diagnostic techniques for registering of the HXR/γ-rays emission and improvement of HXR data analysis methods for RE studies. The HXR spectra have been measured with the sets of HXR spectrometers. This data was numerically processed using special de-convolution procedure allowing a study of evolution of the RE Distribution Function (REDF). Maximal and mean energies of RE populations have been calculated. As well, the detection of spatial distribution of HXR sources in JET plasmas with the JET neutron/γ-rays profile monitor allowed the mapping of RE beams spatial evolution during RE plateaus. In order to increase the HXR/γ-rays diagnostic performance in future JET experiments, the vertical slow spectrometers will be replaced by high-speed LaBr3(Ce) spectrometers allowing measurements with counting rate up to 5*106 sec−1. Also spectrometer with tangential LoS will be replaced by a couple of LaBr3(Ce) and CeBr3 spectrometers. CsI(Tl) detectors in γ-cameras will be substituted by LaBr3(Ce) and CeBr3 crystals coupled with up-to-date SiPM light detectors, which allowed increasing the counting rate of the γ-camera detectors by an order of 10.

Properties of the CsI(Tl) detector elements of the CALIFA detector

In the R3B experiment at FAIR, charged particles with energies up to 600 MeV and forward boosted γ-rays with energies up to 20 MeV need to be detected in scattering experiments. Calorimeters for nuclear physics experiments of this kind, using relativistic radioactive ion beams, require high energy resolution and high efficiency for simultaneous detection of strongly Doppler shifted γ-rays and high-energy charged particles. A calorimeter design that can meet these requirements, using CsI(Tl) scintillators, results in detector elements that may exhibit light output variations with crystal depth, which can limit the attainable resolution. In this paper we present results from a systematic study of 478 detector modules of CALIFA, the R3B calorimeter, in order to determine and minimize such variations. To facilitate further systematic studies we also present results for the total absorption length of the scintillation light, using spectrophotometry, light crosstalk between adjacent detector modules, and surface topography of the CsI(Tl) crystals from atomic force microscopy.