Monoenergetic Γ-rays Research Articles

Gamma-ray lines in 15 years of Fermi-LAT data: New constraints on Higgs portal dark matter

Monoenergetic γ-ray spectral lines are among the cleanest signatures of dark matter annihilation. We analyze 15 years of Fermi-LAT data, find no spectral lines, and place strong constraints on dark matter annihilation to monoenergetic γ-rays. Additionally, we produce the first double-line analysis of the coupled signals from γγ and Zγ lines, which proves particularly powerful for dark matter masses above ∼150 GeV. From our constraints on a double-line feature, we investigate and constrain some minimal models where the Galactic Center Excess can be fit by dark matter annihilation through the Higgs boson into Standard Model particles. Published by the American Physical Society 2024

New measurement of thick target yield for narrow resonance at in the 13C()14N reaction**Project supported by the National Natural Science Foundation of China (Grant No. 11655003).

High energy γ-rays can be used in many fields, such as nuclear waste transmutation, flash photographics, and astrophysics. The 13C()14N resonance reaction was used to generate high energy and mono-energetic γ-rays in this work. The thick-target yield of the 9.17-MeV γ-ray from the resonance in this reaction was determined to be (4.7±0.4)/proton, which was measured by a HPGe detector. Meanwhile, the angular distribution of 9.17-MeV γ-ray was also determined. The absolute efficiency of HPGe detector was calibrated using 56Co and 152Eu sources with known radioactive activities and calculated by GEANT4 simulation.

Real gauge singlet scalar extension of the Standard Model: A possible candidate for cold dark matter

The simplest extension of Standard Model (SM) is considered in which a real SM gauge singlet scalar with an additional discrete symmetry Z 2 is introduced to SM. This additional scalar can be a viable candidate of cold dark matter (CDM) since the stability of S is achieved by the application of Z 2 symmetry on S. Considering S as a possible candidate of CDM, Boltzmann’s equation is solved to find the freeze-out temperature and relic density of S for Higgs mass 120 GeV in the scalar mass range 5 GeV to 1 TeV. As HHSS coupling δ 2 appearing in Lagrangian depends upon the value of scalar mass m S and Higgs mass m h, the m S − δ 2 parameter space has been constrained by using the Wilkinson microwave anisotropy probe (WMAP) limit on the relic density of DM in the Universe and the results of recent ongoing DM direct search experiments, namely CDMS-II, CoGeNT, DAMA, EDELWEISS-II, XENON-10 and XENON-100. From such analyses, two distinct mass regions are found (a lower and higher mass domain) for such a DM candidate that satisfy both the WMAP limit and the experimental results considered here. The possible differential direct detection rates and annual variation of total detection rates have been estimated for this scalar DM candidate S for two detector materials, namely Ge and Xe. Finally, the γ-ray flux has been calculated from the galactic centre due to annihilation of two 130 GeV scalar DM into two monoenergetic γ-rays.

GEANT4 simulations of the DANCE array

The detector for advanced neutron capture experiments (DANCE) at Los Alamos National Laboratory (LANL) is used for neutron capture cross sections measurements. Its high granularity of 160 BaF2 detectors in a 4π geometry allows for highly efficient detection of prompt γ-rays following a neutron capture. The performance of the detector was simulated using the GEANT4 Monte Carlo code. The model includes all 160 BaF2 crystals with realistic dimensions and geometry. The 6LiH shell, beam pipe, crystal wrapping material, aluminum holders, photomultiplier material and materials of the calibration sources were included in the simulation. Simulated γ-ray energy and total γ-ray energy spectra gated on cluster and crystal multiplicities were compared to measured data using 88Y, 60Co, 22Na calibration sources. Good agreement was achieved. A total efficiency and peak-to-total ratio as a function of γ-ray energy was established for mono-energetic γ-rays.

Energy resolution measurements of benzene, toluene and cyclohexane scintillators for monoenergetic γ-rays

Energy resolution and difference of the maximum energy of Compton electrons from the half-height of the Compton edge was measured experimentally for benzene (C 6H 6), cyclohexane (C 6H 12) and toluene scintillators for monoenergetic γ-rays using a γ-γ coincidence technique. For 0.5–1.2 MeV γ-rays, the energy resolution for C 6H 6, C 6H 12 and toluene scintillators varies from 23.8−12.6%, 28.6−2.5% and 23.5−4.6%, respectively. The corresponding energy difference between the maximum Compton electron energy and the half height of the Compton edge for C 6H 6, C 6H 12 and toluene scintillators varies from 13.2−7.6%, 17.7−10.2% and 10.2−6.8%, respectively. The energy resolution of the C 6H 6 detector agrees within 5–10% of that obtained with an identical C 6D 6 scintillator.

Temperature-cycling acceleration factors for aluminum metallization failure in VLSI applications : C. F. Dunn and J. W. McPherson. 28th A. Proc. Reliab. Phys. Symp. (IEEE), 252 (March 1990)

Pulse shape distributions resulting from the interaction of γ-rays in planar germanium detectors were studied as a function of field intensity, γ-ray energy, and detector width. It was observed that at 2300 V/cm the initial rate of charge collection approached 10 nsec/mm. Due to a slow component the total charge collection was about 30% longer. At 1000 V/cm the collection time was somewhat longer, and at 250 V/cm it was considerably longer. These observations appeared to be independent of γ-ray energy in the range of 0.6–3 MeV and detector widths of 3–11 mm. Events interacting near the center of the detector result in fast rising pulses and those interacting near one of the electrodes have a risetime which is approximately twice as long, thus giving rise to a distribution of pulse shapes. With low energy γ-rays all shapes occur with equal probability, but at higher energy the pulses tend to have a more uniform shape. Due to the spread in risetimes, signals from monoenergetic γ-rays do not cross a given pulse height level at the same time and therefore produce timing uncertainties. With a 1 cm detector timing uncertainties of more than 30 nsec have been observed at the 50% level, and less than 5 nsec at the 5% level. It therefore appears that for accurate timing of all signals, the timing discriminator should be set at the lowest level consistent with the system noise. The variations in risetime can also affect the energy resolution. If a 1 cm detector is used in conjunction with a pulse shaping network consisting of a 1 μsec RC differentiator and integrator, the variations in risetimes may cause an amplitude spread on the order of 0.03%. At γ-ray energies of 10 MeV this is comparable to the spread due to statistics.

X-rays expected from supernova 1987A compared with the source discovered by the Ginga satellite

The X-ray astronomy satellite Ginga has detected X-rays from the region of supernova 1987 A1. The location and hard spectrum of this X-ray source make it a strong candidate for SN1987A1,2. Among the possible mechanisms of X-ray emission from SN1987A3,4, including the collision of the ejecta with circumstellar matter, non-thermal radiation from a pulsar, is Compton scattering of monoenergetic γ-rays from the radioactive decay 56Ni→56Co→ 56Fe (refs 3, 5–7). It is clear that radioactive decays are powering the optical emission of SN1987A because its luminosity is now declining exponentially with the 56Co decay rate8,9. We have constructed hydrodynamic models of SN1987A and calculated the optical light curve and the X-ray light curve and spectrum from 56Co decay. For the optical light curve, the model agrees better with the observations if some 56Co is mixed into outer layers rather than being confined to the deepest layer of the ejecta. Such mixing has much larger effects on the X-ray light curve. Without the mixing of 56Co, X-rays would not be observable by Ginga until ˜250 d after the explosion. With mixing the X-rays emerge much earlier. X-ray emission from radioactive decay may therefore qualitatively account for the hard component of X-rays from SN1987A observed by Ginga, if 56Co has been mixed into the outer layers. The soft component of the spectrum cannot be explained by the radioactive model and must be due to another mechanism.

Use of the random sum peak in the determination of the resolving time of NaI(TI) scintillation detectors

Photopeak and random sum peak due to monoenergetic γ-rays from 203Hg, 54Mn, 51Cr and 137Cs can be used to determine the resolving time of resolving time of NaI(TI) scintillation detectors. The method, which proved to be simple and reliable, is described.

A Monte Carlo program for evaluating the response of a scintillation counter to monoenergetic gamma rays

A simple technique is described for calculating the response of a Nal scintillation counter to monoenergetic γ-rays. The method employs empirically determined counter parameters and γ-ray cross-sections in a Monto Carlo routine and has been successfully applied in the analysis of internal bremsstrahlung spectra.

Angular distributions of 238U photofission fragments

Abstract Angular distributions of fragments from the photofission of 238 U were measured for discrete excitation energies in the range 5.6–9 MeV. Monoenergetic γ-rays from radiative neutron capture were used to produce the excitation and solid-state particle-track recorders were used as fragment detectors. From the measured angular distributions, the barrier heights and curvatures for three low-energy fission channels in the transition state nucleus were deduced.

Calculated relative efficiency for coaxial and planar Ge(Li) detectors

With the aid of a Monte Carlo computer program, the relative efficiency to monoenergetic γ-rays of coaxial and planar Ge(Li) detectors has been calculated. Considering a point source, placed on the extended axis of the detector, at a fixed distance, radiations of different energies are generated within the solid angle subtended by the crystal. The gamma-rays impinging on the detector are followed until a fraction whatsoever of their energy escapes from the active region of the crystal. If the γ-ray releases all its energy in the active region, a photopeak is counted and then its efficiency is calculated. At the end of the program the efficiency for the double-escape peak is also obtained. Following this procedure the photopeak efficiency was calculated for three Ge(Li) detectors, having volumes of: 2.0 cm 3 (planar), 5.3 cm 3 and 30 cm 3 (coaxial) from ≈ 100 keV up to 4000 keV. By means of these calculated efficiency curves, the well measured gamma-ray relative intensities in sources as 22Na, 88Y, 207Bi, 133Ba and ThC″ could be reproduced to within 1%–3%.

A simple and versatile gamma-ray source for the calibration of high-energy Ge(Li) spectra

A simple and inexpensive source of mono-energetic high-energy γ-rays of many different energies, suited for the energy-calibration of Ge(Li) spectra, is described.

Cross sections for the photofission of 232Th, induced by mono-energetic gamma rays of 12 different energies

Thorium-loaded nuclear emulsions have been exposed to mono-energetic γ-rays obtained from (n, γ) reactions on the following elements: S, Dy, Y, Ca, Ti, Be, Mn, Pb, Fe, Al, Cu and Ni. The photo-fission cross section of 232Th has been measured at 12 energies in the range 5.4–9 MeV. For the same energies, the ratios of the 232Th cross section with respect to 238U are also given.

Angular distribution of 238U photofission fragments for 12 different mono-energetic γ-rays

Mono-energetic γ-rays of 12 different energies in the energy range 5.4–9 MeV have been used to irradiate 238U. The results of measurements of angular distributions of photofission fragments are reported and discussed. An analysis assuming penetration barrier function has been performed, and energies of the K-levels have been obtained as well as other nuclear parameters.

A Simple Calculation for Air-Scattered Gamma-Rays

A simple formula for air-scattered γ-rays is proposed. The proposed formula is derived using a single-scattering approximation, with exponential attenuation and buildup factor for scattered γ-ray energy. The results of calculation obtained with the formula are compared with those by Monte Carlo method, and by single-scattering calculation without exponential attenuation and buildup, for line beams of mono-energetic γ-rays emitted from a point source. For higher energies, the air-scattered flux and dose rate given by this simple approximation agree fairly well with the Monte Carlo calculations at all beam angles and source-detector distances. The accuracy is within about 10%. The flux and dose rate for γ-rays emitted isotropically from the point source have also been calculated, and are presented as a function of distance.

A Simple Calculation for Air-Scattered Gamma-Rays

A simple formula for air-scattered γ-rays is proposed. The proposed formula is derived using a single-scattering approximation, with exponential attenuation and buildup factor for scattered γ-ray energy. The results of calculation obtained with the formula are compared with those by Monte Carlo method, and by single-scattering calculation without exponential attenuation and buildup, for line beams of mono-energetic γ-rays emitted from a point source. For higher energies, the air-scattered flux and dose rate given by this simple approximation agree fairly well with the Monte Carlo calculations at all beam angles and source-detector distances. The accuracy is within about 10%. The flux and dose rate for γ-rays emitted isotropically from the point source have also been calculated, and are presented as a function of distance.

Pulse shape distributions from gamma-rays in lithium drifted germanium detectors

Pulse shape distributions resulting from the interaction of γ-rays in planar germanium detectors were studied as a function of field intensity, γ-ray energy, and detector width. It was observed that at 2300 V/cm the initial rate of charge collection approached 10 nsec/mm. Due to a slow component the total charge collection was about 30% longer. At 1000 V/cm the collection time was somewhat longer, and at 250 V/cm it was considerably longer. These observations appeared to be independent of γ-ray energy in the range of 0.6–3 MeV and detector widths of 3–11 mm. Events interacting near the center of the detector result in fast rising pulses and those interacting near one of the electrodes have a risetime which is approximately twice as long, thus giving rise to a distribution of pulse shapes. With low energy γ-rays all shapes occur with equal probability, but at higher energy the pulses tend to have a more uniform shape. Due to the spread in risetimes, signals from monoenergetic γ-rays do not cross a given pulse height level at the same time and therefore produce timing uncertainties. With a 1 cm detector timing uncertainties of more than 30 nsec have been observed at the 50% level, and less than 5 nsec at the 5% level. It therefore appears that for accurate timing of all signals, the timing discriminator should be set at the lowest level consistent with the system noise. The variations in risetime can also affect the energy resolution. If a 1 cm detector is used in conjunction with a pulse shaping network consisting of a 1 μsec RC differentiator and integrator, the variations in risetimes may cause an amplitude spread on the order of 0.03%. At γ-ray energies of 10 MeV this is comparable to the spread due to statistics.

Results on the cross-section of238U-fission induced by low-energy monoenergetic γ-rays

Results on the cross-section of238U-fission induced by low-energy monoenergetic γ-rays

Pulse Shape Distributions from Gamma-Rays in Lithium Drifted Germanium Detectors

Pulse shape distributions resulting from the interaction of γ-rays in germanium detectors were studied as a function of field intensity, γ-ray energy, and detector width. It was observed that at 2300 V/cm the initial rate of charge collection approached 10 nsec/mm. Due to a slow component the total charge collection was about 30% longer. At 1000 V/cm the collection time was somewhat longer, and at 250 V/cm it was considerably longer. These observations appeared to be independent of γ-ray energy in the range of 0.6 - 3 MeV, and detector widths of 3 - 11 mm. Events interacting near the center of the detector result in fast rising pulses and those interacting near one of the electrodes have a risetime which is approximately twice as long, thus giving rise to a distribution of pulse shapes. With low energy γ-rays all shapes occur with equal probability, but at higher energy the pulses tend to have a more uniform shape. Due to the spread in risetimes, signals from monoenergetic γ-rays do not cross a given pulse height level at the same time and therefore produce timing uncertainties. With a 1 cm detector timing uncertainties of more than 30 nsec have been observed at the 50% level, and less than 5 nsec at the 5% level. It therefore appears that for accurate timing of all signals, the timing discriminator should be set at the lowest level consistent with the system noise. The variations in risetime can also affect the energy resolution.

Sources of quasi-monoenergetic γ - radiation—II

The use of Ba 133 as a source of approximately monoenergetic γ-rays is discussed and the preparation of suitable sources is described.