Fore-aft asymmetry of the 2H(n,γ)3H at very low energies

We have used the recent effective field theory (EFT) which is constructed from two-and three-nucleon interactions, using minimal substitution in the momentum dependence of these interactions. We present the calculations of the fore-aft asymmetry of γ-rays in the reaction ²H(n,γ)³H which are based on EFT up to next-to-next-to leading order (N²LO). The results are compared with the recently reported calculations and measurements of the fore-aft asymmetry of γ-rays from neutron-deuteron radiative capture. The calculated fore-aft asymmetry of the nd radiative capture process above deuteron breakup threshold is in good agreement with the available experimental data up to 20 MeV.     

Low-Energy Direct Capture in the ^12C（α, γ）^16O Reaction

The spectra of light nuclei provide the first test of nuclear interaction models. The reaction amount determines the relative abundance of most elements in red giant stars, neutron stars, and black holes. Due to the fact that this reaction occurs at low energies, the experimental measurement is very difficult and perhaps impossible. In this work, the radiative capture of the ^12C（α, γ）^16O reaction at very low-energies is taken as a case study. Using the M3Y potential we calculate the astrophysical Factor for transition E1 and E2. In comparison with other theoretical methods and available recent experimental data, excellent agreement is achieved for the astrophysical S-factor of this process.     

Maxwellian Averaged Neutron Capture Cross Sections in 56Fe and 57Fe

Measurements of the keV-neutron capture cross sections and radiative γ-ray spectrum of 56Fe and 57Fe are performed based on a 7 Li（p,n）7 Be reaction neutron source. The incident neutron spectrum on a capture sample is measured by means of a time-of-flight （TOF） method with a 6Li-glass detector. The radiative capture 7-rays emitted from an iron CS Fe or 57 Fe） or standard gold （197Au） sample are detected by a large anti-Compton NaI（TI） spectrometer covered with a heavy shield. The capture yields of samples are obtained by applying a pulse-height weighting technique to the corresponding capture γ-ray pulse-height spectrum. The Maxwellian averaged neutron capture cross sections of 56Fe and 5T Fe are derived according to the present capture cross section results.     

On the detectability of Galactic dark matter annihilation into monochromatic gamma-rays

Monochromatic γ-rays are thought to be the smoking gun signal for identifying dark matter annihilation. However, the flux of monochromatic γ-rays is usually suppressed by virtual quantum effects since dark matter should be neutral and does not couple with γ-rays directly. In this work, we study the detection strategy of the monochromatic γ-rays in a future space-based detector. The flux of monochromatic γ-rays between 50 GeV and several TeV is calculated by assuming the supersymmetric neutralino as a typical dark matter candidate. The detection both by focusing on the Galactic center and in a scan mode that detects γ-rays from the whole Galactic halo are compared. The detector performance for the purpose of monochromatic γ-ray detection, with different energy and angular resolution, field of view, and background rejection efficiencies, is carefully studied with both analytical and fast Monte-Carlo methods.     

Astrophysical S-factor of the 12C（α,γ） 16O reaction at solar energies

The astrophysical S-factor of the 4He＋12C radiative capture is calculated in the potential model at the energy range 0.1-2.0 MeV. Radiative capture 12C（α,γ） 16O is extremely relevant for the fate of massive stars and determines if the remnant of a supernova explosion becomes a black hole or a neutron star. Because this reaction occurs at low energies, the experimental measurements are very difficult and perhaps impossible. In this paper, radiative capture of the 12C（α,γ） 16O reaction at very low energies is taken as a case study. In comparison with other theoretical methods and available experimental data, good agreement is achieved for the astrophysical S-factor of this process.     

Astrophysical S-factor of the ~(12)C(α, γ)~(16)O reaction at solar energies

The astrophysical S-factor of the4He+12C radiative capture is calculated in the potential model at the energy range 0.1-2.0 MeV.Radiative capture12C(α,γ)16O is extremely relevant for the fate of massive stars and determines if the remnant of a supernova explosion becomes a black hole or a neutron star.Because this reaction occurs at low energies,the experimental measurements are very difficult and perhaps impossible.In this paper,radiative capture of the12C(α,γ)16O reaction at very low energies is taken as a case study.In comparison with other theoretical methods and available experimental data,good agreement is achieved for the astrophysical S-factor of this process.     

Shanghai laser electron gamma source and its applications

Shanghai Laser Electron Gamma Source, a high intensity beam line of γ-ray, is expected to generate γ-rays up to the maximum energy of 22 MeV by Compton backscattering between a CO₂ laser and electrons in the 3.5 GeV storage ring of the Shanghai Synchrotron Radiation Facility. The luminosity of SLEGS γ-ray beam is estimated to be 7×10⁷ A^－1W^－1s^－1 in a optimized setup. Indirect measurement of cross section of the key nuclear-astrophysics reaction ¹²C(α,γ)¹⁶O and γ-ray-triggered transmutation of long-lived radioactive wastes are discussed based on the estimated SLEGS γ-ray beam properties.     

Systematical law of (n, γ) reaction cross sections of even-even nuclei

We have derived a formula for the neutron radiative capture cross section in the framework of a statistical model approach to nuclear reactions. Based on this formula, new systematics are established between the (n, γ) reaction cross section and the energy level density of a compound nucleus or a relative neutron excess of an even-even target nucleus for neutron incident energy above the resonance region to MeV. Good agreement with experimental data suggests that this new systematical law is helpful to analyze the experimental data.     

A capture-gated fast neutron detection method

To address the problem of the shortage of neutron detectors used in radiation portal monitors(RPMs),caused by the ~3He supply crisis, research on a cadmium-based capture-gated fast neutron detector is presented in this paper. The detector is composed of many 1 cm × 1 cm × 20 cm plastic scintillator cuboids covered by 0.1 mm thick film of cadmium. The detector uses cadmium to absorb thermal neutrons and produce capture γ-rays to indicate the detection of neutrons, and uses plastic scintillator to moderate neutrons and register γ-rays. This design removes the volume competing relationship in traditional ~3He counter-based fast neutron detectors, which hinders enhancement of the neutron detection efficiency. Detection efficiency of 21.66% ± 1.22% has been achieved with a 40.4 cm × 40.4cm × 20 cm overall detector volume. This detector can measure both neutrons and γ-rays simultaneously. A small detector(20.2 cm × 20.2 cm × 20 cm) demonstrated a 3.3 % false alarm rate for a ~(252)Cf source with a neutron yield of 1841 n/s from 50 cm away within 15 s measurement time. It also demonstrated a very low(0.06%) false alarm rate for a 3.21 × 10~5 Bq ~(137)Cs source. This detector offers a potential single-detector replacement for both neutron and the γ-ray detectors in RPM systems.     

Matching Condition in γ-γ Annihilation Absorption

Two-photon annihilation (γ-γ reaction) is an important absorption mechanism in γ-ray physics and γ-ray astronomy. Using the markedly simplified direction-averaged cross section of annihilation σ^-(ω,ω’) for a normal isotropic ambient radiation field around the γ-ray source, we obtain a matching condition for the energies of two interacting photons, which ensures the attainment of the maximum annihilation probability. This is a new result that is helpful to obtain a better understanding for the absorption behaviour in the γ-γ annihilation process,and this predicts some possible line-like absorption structures in the emergent γ-ray continuous spectra. Some inferences of the matching condition are also presented.     

THE NUCLEAR STRUCTURE AND BACKBENDING PHENOMENON FOR 114-130Xe ISOTOPES

In view of interacting boson fermion formalism, a microscopic sdIBM-2 +2q.p. model is used to describe the ground-state band, β-band, γ-band and two-quasi-particle band for ^114-130Xe isotopes. The theoretical investigations indicate that the backbending is caused by crossing of the two-quasi-proton band and the ground-state band. This result seems to provide a possible way for understanding the backbending phenomenon of ^114-130Xe isotopes.     

In searches for daemons

A possibility is considered of detecting Planckian particles carrying an electric charge Z≈10 and supposedly forming the dark matter of the Galactic disk, whence they are captured by combined action of the Sun and the Earth into strongly elongated Earth-crossing orbits. The flux of such dark electric matter objects, daemons, at the Earth’s orbit may reach f _⊕≈3×10⁻⁷cm⁻²s⁻¹ at a velocity about 52 km/s. Negatively charged daemons are capable of catalyzing the fusion of light (Z _n<10) nuclei. The rate of capture (and fusion) of nuclei should be particularly high in a metallic phase. A detection system is described that consists of beryllium plates 45 mm thick and 1200 cm² in area coated with a ZnS(Ag) scintillator. It is assumed that the products of the fusion reaction 2⁹Be → ¹⁸O that are ejected in amounts of up to about 10⁴ from the points of daemon entrance and exit would give rise to scintillations with a delay of about 1μs. An exposure of the system for 300 h revealed no event. The reason for the negative result can be (1) too optimistic an estimate of the flux (the inclusion of some factors could lower it by 1.5–3 orders of magnitude) and (2) the poisoning of the catalyst by capture of nuclei with Z _n≥10. The time required for the recovery of the daemon catalytic properties is estimated from the analysis of the energy release in the Sun at no less than 3×10⁻⁷ s. The analysis of the total available data suggests that the daemon flux at the Earth is about 3×10⁻⁸ cm⁻² s⁻¹. The experiments will be continued. From Yadernaya Fizika, Vol. 63, No. 6, 2000, pp. 1112–1117. Original English Text Copyright ? 2000 by Drobyshevski. This article was submitted by the author in English.     

Measurement of anomalous nuclear reaction in deuterium-loaded metal

This paper reports on an experiment for testing natural nuclear fusion at low temperature searching for evidence of the origin of ³He from natural nuclear fusion in deep Earth. The experiment was carried out using deuterium-loaded titanium foil samples and powder sample. Detection of charged particle was carried out using a low-level charged particle spectrometer. An Al foil was used as an energy absorber for identification of charged particle. Although the counting rate is very low in the experiment, the emission of energetic particle from the sample is observed and the particle is identified as a proton having energy about 2.8 MeV after exiting the titanium sample. This work provides a positive result for the emission of charged particle in the deuterium-loaded titanium foil samples at low temperature, but a negative result for the deuterium-loaded titanium powder sample. The average reaction yield is deduced to be (0.46±0.08) protons/h for the foil samples. With the suggestion that the proton originates from d--d reaction, we calculate the reaction rate for d--d reaction, and the obtained result is 1.4× 10^-24 fusion/d--d\cdot sec. The negative result of the deuterium-loaded titanium powder sample suggests that the reaction yield might be correlated with the density or microscopic variables of deuterium-loaded titanium materials. The negative result also indicates that d--d reaction catalysed by μ-meson from cosmic ray can be excluded in the samples in this experiment.     

Hadronic Scenarios for Gamma-Ray Emission from Three Supernova Remnants Interacting with Molecular Clouds

GeV γ-rays detected with the large area telescope on board the Fermi Gamma-ray space telescope in the direc- tion of HB21, MSH 17-39 and G337.0-0.1 have been recently reported. The three supernova remnants （SNRs） show interactions with molecular clouds, and they are effective gamma-ray emitters as the relativistic protons accelerated by the SNR shocks inelastically colliding with the dense gas in the clouds. The origin of the observed γ-rays for the three remnants is investigated in the scenario of the diffusive shock acceleration. In the model, a part of the SNR shock transmits into the nearby molecular clouds, and the shock velocity is greatly reduced. As a result, a shock with a relatively low Alfven Mach number is generated, and the spectra of the accelerated protons and thee＇γ-ray photons produced via proton-proton interaction can be obtained. The results show that the observed γ-ray spectra for the three SNRs interacting with the molecular clouds can be reproduced. It can be concluded that the hadronic origin of the γ-rays for the three SNRs is approved, and the ability of SNR shocks to accelerate protons is also supported.     

Calculation of astrophysical reaction rate of 82Ge(n,γ)83Ge

The neutron capture reaction on a neutron-rich near closed-shell nucleus ⁸²Ge may play an important role in the r-process following the fallout from nuclear statistical equilibrium in core-collapse supernovae. By carrying out a DWBA analysis for the experimental angular distribution of ⁸²Ge(d, p)⁸³Ge reaction we obtain the single particle spectroscopic factors, S_2,5/2 and S_0,1/2 for the ground and first excited states of ⁸³Ge=⁸²Ge⊙n, respectively. And then these spectroscopic factors are used to calculate the direct capture cross sections for the ⁸²Ge(n, γ)⁸³Ge reaction at energies of astrophysical interest. The optical potential for neutron scattering on unstable nucleus ⁸²Ge is not known experimentally. We employed a real folding potential which was calculated by using the proper ⁸²Ge density distribution and an effective nucleon-nucleon force DDM3Y. The neutron capture reactions on neutron-rich closed-shell nuclei are expected to be dominated by the direct capture to bound states. We will show that the direct capture rates on these nuclei are sensitive to the structure of the low-lying states.     

A study on the decay of ^72As

The excited states of the ⁷²Ge nucleus were investigated in radioactive decay of ⁷²As. Three new transitions with 1996.58, 2125.59 and 2255.49keV have been found for the first time. One γ-ray with 912.09keV has been placed in the decay scheme for the first time, and the placement of 1938.88, 2116.79, 2785.59, 2833.03, 2950.69 and 3338.00keV γ-rays are confirmed again in the present work. One new level at 2027.72keV excitation energy is proposed. The level scheme was established and for a number of levels spin-parity assignments are suggested on the basis of logft values and γ-branching ratios.     

Average Energy Loss Measured in Single and Double Electron Capture Collisions of He^2＋ on Ar at Low Velocities ＊

Employing the recoil ion momentum spectroscopy we investigate the collision between He^2＋ and argon atoms. By measuring the recoil longitudinal momentum the energy losses of projectile are deduced for capture reaction channels. It is found that in most cases for single- and double-electron capture, the inner electron in the target atom is removed, the recoil ion is in singly or multiply excited states （hollow ion is formed）, which indicates that electron correlation plays an important role in the process. The captured electrons prefer the ground states of the projectile. It is experimentally demonstrated that the average energy losses are directly related to charge transfer and electronic configuration     

Halo Effect on Direct Neutron Capture Process

We calculate the capture cross sections of the ^10Be(n,γ) ^11Be reaction by means of the asymptotic normalization coefficient method and demonstrate the halo effects on the capture cross sections for the direct radiative neutron capture where a p-, s- or d-wave neutron is captured into an s-orbit or p-orbit in ^11Be by emitting an E1 γ-ray, respectively. The result shows that the enormous enhancement of the capture cross section is just due to the large overlap of the incident neutron wave with the extended tail of the ha/o, which is clearly illustrated by the reduced transition amplitude function.     

Leptonic Origin of TeV Gamma-Ray Emission from Crab Nebula

We study the nonthermal emission of the Crab nebula in the bands from radio to TeV γ-ray on a simplified timedependent injection model. In this model, relativistic electrons in the Crab nebula consists of two components and their injected spectrum is a broken power law with different indices and a break energy. The relativistic electrons emit nonthermal photons through synchrotron and inverse Compton scattering off soft photon fields inside the nebula. The resulting spectrum calculated with the model is well consistent with the observed data ranging from radio to very high energy γ-rays for the Crab nebula, where the emission from radio to medium γ-rays is from electron＇s synchrotron emission, whereas the emission above ～ 100 MeV primarily comes from the inverse Compton scattering of the relativistic electrons on synchrotron photons.