Angular Distribution Of Gamma Rays Research Articles

Measurement of the Yield and Angular Distributions of Gamma Rays Originating from the Interaction of 14.1-MeV Neutrons with Chromium Nuclei

The reaction induced by the inelastic scattering of 14.1-MeV neutrons on chromium nuclei is studied by means of the tagged-neutron method at the TANGRA (TAgged Neutrons and Gamma RAys) facility deployed at Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, and based on the ING-27 standard neutron generator. The energies of visible gamma transitions occurring in various reactions of neutron interaction with chromium nuclei and their partial cross sections are determined. The results obtained by measuring the angular distribution of gamma rays for $${}^{52}$$ Cr are analyzed and are compared with respective results of other experimental studies available in the literature.

Neural Network Estimation for Attenuation Coefficients for Gamma-Ray Angular Distribution

Spins of nuclear states (J) and multipolarities of gamma rays are usually investigated by the angular distribution of gamma rays emitted from aligned states formed by nuclear reactions. In the case of partial alignment, attenuation coefficients are used in angular distribution function. These coefficients are tabulated in literature for different J values. However, these coefficients involve $$r$$ -fold tensor products. Furthermore, as the calculation of these coefficients implicitly involves highly complicated integral quantities, they are very difficult to handle explicitly for larger $$r$$ values. In this respect, universal nonlinear function approximator layered feedforward neural network (LFNN) can be applied to construct consistent empirical physical formulas (EPFs) for physical phenomena. In this paper, we consistently estimated the attenuation coefficients by constructing suitable LFNNs. The LFNN-EPFs fitted the literature coefficient data very well. Moreover, magnificent LFNN test set predictionson unseen data confirmed the consistent LFNN-EPFs for the determination of coefficients.

Consistent Empirical Physical Formula Construction for Gamma Ray Angular Distribution Coefficients by Layered Feedforward Neural Network

Multipolarities of gamma rays and spins-parities of nuclear states are usually investigated by the angular distribution of gamma rays emitted from aligned states formed by nuclear reactions. For different multipolarities of the transitions, the distribution shows different characteristics. The distribution is obtained by using angular distribution formula which has literature tabulated coefficients for different spins and multipolarities. However, these coefficients involve -fold tensor products and they are highly nonlinear in nature. Furthermore, as the calculation of these coefficients implicitly involves highly complicated integral quantities, they are very difficult to handle explicitly for larger values. In this respect, as we theoretically proved in a previous paper, universal nonlinear function approximator layered feedforward neural network (LFNN) can be applied to construct consistent empirical physical formulas (EPFs) for nonlinear physical phenomena. In this paper, by concentrating on the integer spins of nuclear states and dipole and quadrupole type multipolarities of the transitions, we consistently estimated the coefficients by constructing suitable LFNNs. The LFNN-EPFs fitted the literature coefficient data very well. Moreover, magnificent LFNN test set forecastings over previously unseen data confirmed the consistent LFNN-EPFs for the determination of coefficients. In this sense, we can conclude that the LFNN consistently infers nonlinear physical laws governing the angular distribution of gamma rays, which are otherwise difficult to obtain by conventional coefficient calculation methods.

Novel gamma-ray signatures of PeV-scale dark matter

The gamma-ray annihilation and decay products of very heavy dark matter particles can undergo attenuation through pair production, leading to the development of electromagnetic cascades. This has a significant impact not only on the spectral shape of the gamma-ray signal, but also on the angular distribution of the observed photons. Such phenomena are particularly important in light of the new HAWC experiment, which provides unprecedented sensitivity to multi-TeV photons and thus to very heavy dark matter particles. In this study, we focus on dark matter in the 100 TeV–100 PeV mass range, and calculate the spectral and angular distribution of gamma-rays from dwarf galaxies and from nearby galaxy clusters in this class of models.

Synchrotron radiation, pair production, and longitudinal electron motion during 10-100 PW laser solid interactions

At laser intensities above 1023 W/cm2, the interaction of a laser with a plasma is qualitatively different to the interactions at lower intensities. In this intensity regime, solid targets start to become relativistically underdense, gamma-ray production by synchrotron emission starts to become an important feature of the dynamics and, at even higher intensities, electron-positron pair production by the non-linear Breit-Wheeler process starts to occur. In this paper, an analysis is presented of the effects of target density, laser intensity, target preplasma properties, and other parameters on the conversion efficiency, spectrum, and angular distribution of gamma-rays by synchrotron emission. An analysis of the importance of Breit-Wheeler pair production is also presented. Target electron densities between 1022 cm−3 and 5 × 1024 cm−3 and laser intensities covering the range between 1021 W/cm2 (available with current generation laser facilities) and 1024 W/cm2 (upper intensity range expected from the ELI facility are considered. Results are explained in terms of the behaviour of the head of the laser pulse as it interacts with the target.

No evidence for gamma-ray halos around active galactic nuclei resulting from intergalactic magnetic fields

We analyze the gamma-ray halo around stacked AGNs reported in Ap.J.Lett., 2010, 722, L39. First, we show that the angular distribution of gamma-rays around the stacked AGNs is consistent with the angular distribution of the gamma-rays around the Crab pulsar, which is a point source for Fermi/LAT. This makes it unlikely that the halo is caused by an electromagnetic cascade of TeV photons in the intergalactic space. We then compare the angular distribution of gamma-rays around the stacked AGNs with the point-spread function (PSF) of Fermi/LAT and confirm the existence of an excess above the PSF. However, we demonstrate that the magnitude and the angular size of this effect is different for photons converted in the front and back parts of the Fermi/LAT instrument, and thus is an instrumental effect.

Parity violation in neutron–proton capture—The NPDGamma experiment

The NPDGamma collaboration has recently completed the first phase of a measurement to determine the size of the weak nucleon–nucleon interaction from cold neutron capture on a liquid hydrogen target. In the framework of the nearly 30 year old DDH model [B. Desplanques, J.F. Donoghue, B.R. Holstein, Annals of Physics 124 (1980) 449], the measured process is explained in terms of the weak pion–nucleon coupling, while the framework of modern effective field theory parameterizes the measured process in terms of the S 1 3 - P 1 3 , long range transition (essentially the Danilov parameter ρ t ) [S.L. Zhu et al., Nuclear Physics A 748 (2005) 435; C.-P. Liu, Phys. Rev. C 75 (2007) 065501]. The couplings in terms of either model are directly proportional to the parity violating up-down asymmetry in the angular distribution of gamma rays with respect to the neutron spin direction in the reaction n ⇒ + p → d + γ . The asymmetry has a predicted size of 5 × 10 - 8 and the aim of the NPDGamma collaboration is to measure it to 20%. The first phase of the measurement was completed at the Los Alamos National Laboratory Neutron Science Center Spallation Source with a preliminary result of ( - 1.1 ± 2.1 stat . ± 0.2 sys . ) × 10 - 7 . Here, we report on the measurements and the results obtained so far. The experiment is currently being installed at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, for the remainder of its run time.

Parameterization of the Angular Distribution of Gamma Rays Produced byp‐pInteraction in Astronomical Environments

We present the angular distribution of gamma rays produced by proton-proton interactions in parameterized formulae to facilitate calculations in astrophysical environments. The parameterization is derived from Monte Carlo simulations of the up-to-date proton-proton interaction model by Kamae et al. (2005) and its extension by Kamae et al. (2006). This model includes the logarithmically rising inelastic cross section, the diffraction dissociation process and Feynman scaling violation. The extension adds two baryon resonance contributions: one representing the {Delta}(1232) and the other representing multiple resonances around 1600 MeV/c{sup 2}. We demonstrate the use of the formulae by calculating the predicted gamma-ray spectrum for two different cases: the first is a pencil beam of protons following a power law and the second is a fanned proton jet with a Gaussian intensity profile impinging on the surrounding material. In both cases we find that the predicted gamma-ray spectrum to be dependent on the viewing angle.

Calculation of the characteristics of the external irradiation of a human being as a result of 137Cs contamination of soil

Monte Carlo estimates of the effect of certain characteristics of the external irradiation of a human being standing on the surface of soil contaminated with 137Cs are presented. The spectrum and angular distribution of gamma rays in air and the effect of the height of the individual’s position above the soil surface, the area of the contaminated surface, the contamination depth in the soil, the snow cover, and the walls of a room are estimated. The effect of a change in certain computational parameters on the results is examined. It is shown that the density of the phantom material and soil have the strongest effect on the computational results.

Commissioning of the NPDGamma Detector Array: Counting Statistics in Current Mode Operation and Parity Violation in the Capture of Cold Neutrons on B 4 C and (27) Al.

The NPDGamma γ-ray detector has been built to measure, with high accuracy, the size of the small parity-violating asymmetry in the angular distribution of gamma rays from the capture of polarized cold neutrons by protons. The high cold neutron flux at the Los Alamos Neutron Scattering Center (LANSCE) spallation neutron source and control of systematic errors require the use of current mode detection with vacuum photodiodes and low-noise solid-state preamplifiers. We show that the detector array operates at counting statistics and that the asymmetries due to B4C and (27)Al are zero to with- in 2 × 10(-6) and 7 × 10(-7), respectively. Boron and aluminum are used throughout the experiment. The results presented here are preliminary.

Angular distribution of two-photon positron annihilation in low energy positron scattering by the hydrogen molecular ion

Calculations are carried out to determine the angular distribution of gamma rays resulting from positron annihilation when low-energy positrons are scattered by the hydrogen molecular ion. Angular distributions calculated using wavefunctions from a variational Kohn calculation are compared with those obtained using the Coulomb - Born approximation. The angular distribution function calculated with the most accurate wavefunction gives a half width half maximum value of 3.42 mrad for incident positrons with momentum .

A stochastic model for transient magnetic fields as observed by perturbed angular distribution of gamma rays

A stochastic model is introduced to study the transient magnetic field (TF) experienced by the nuclei of fast ions traversing a ferromagnetic medium. The field is assumed to arise primarily from the bound electrons of the ion, polarized by the internal magnetic field of the ferromagnetic specimen. Spin-flip scattering is considered to be the dominant mechanism for polarization transfer from the host to the ion. Electron capture and loss mechanisms are also taken into account in a phenomenological manner. An analytical expression is derived for the TF which depends on the electron capture and loss cross-sections. The result for the perturbation factor is shown to be more general than that derived by Abragam and Pound and reduces to their result in the appropriate limit.

Calibration of the transient field for Pt ions in gadolinium and magnetic moments of the 21+ states in 196,198Pt.

The precession of the angular distribution of gamma rays deexciting the ${2}_{1}^{+}$ states of $^{194,196,198}\mathrm{Pt}$ and $^{148}\mathrm{Nd}$ nuclei have been measured by the transient field method. Average values of the transient field acting at Pt and Nd ions recoiling through gadolinium have been obtained from these data, and are shown to validate the Rutgers parametrization in the recoil velocity range 1.9\ensuremath{\le}(v/${\mathit{v}}_{0}$)=4.6. The g(${2}_{1}^{+}$) factors of $^{196,198}\mathrm{Pt}$ relative to g${(}^{194}$Pt)=0.302(16) have also been deduced: g${(}^{196}$Pt)=0.302(24) and g${(}^{198}$Pt)=0.350(30), in good agreement with other transient field measurements.

The angular distribution of gamma-rays from thermal high-spin giant-dipole-resonances on superdeformed states

The microscopic approach with thermal RPA based on thermal CHFB ensemble is applied to the analysis of the angular distribution coefficient of γ-rays, a 2( E γ ), in addition to the spectrum shapes of σ abs ( E γ ), both for the ground band with small prolate deformation and for the superdeformed band in 132Ce. The critical γ-ray energy where a 2( E γ ) changes its sign is much lower for the superdeformed band than for the ground band. Thermal energy-weighted sum-rule gives an account for the decrease of the peak height of σ abs ( E γ ) with increasing temperature.

Nuclear orientation study of the decay of208At (T 1/2=1.63 h) and209At (T 1/2=5.41 h) implanted in iron host

We have measured the angular distribution of gamma-rays in 208,209Po following the decay of the mass-separated isotopes 208,209At polarized at low temperatures in an iron host. Multipole mixing ratios were deduced for 14 and 9 gamma-ray transitions in 208Po and 209Po, respectively, and unambiguous spin-assignments were made for several levels in both nuclei.

Measurement of the angular distribution of gamma rays emitted in the three photon annihilation of positrons and electrons

We have measured the angular distribution of gamma rays emitted in three photon annihilation of positrons and electrons by the triple fast coincidence method. The experimental data are in agreement with the quantum electrodynamics (QED) prediction within the error.

Investigation of low-spin states of140Ce in the (n,n'γ) reaction and within the shell model

Low-spin levels of 140Ce were studied by means of the (n,n' gamma ) reaction using reactor fast neutrons. Excited states up to an excitation energy of 3.5 MeV and with spin values up to 6 were found to be populated. Energies, intensities and angular distribution of gamma rays attributed to 140Ce have been measured. In addition to verifying known level characteristics, a spin assignment Jpi =4+ was found for the 2515.8 keV level. The existence of levels at 2628.9, 3001.3, 3395.7 and 3473.8 keV excitation energy was confirmed. Multipole mixing ratios have been extracted for nine of the most intense gamma -ray transitions. The experimental level energies and several electromagnetic properties are compared with shell-model predictions.

Investigation of low-spin states of138Ba in the (n,n' γ) reaction and within the shell model

Low-spin levels of 140Ce were studied by means of the (n,n' gamma ) reaction using reactor fast neutrons. Excited states up to an excitation energy of 3.5 MeV and with spin values up to 6 were found to be populated. Energies, intensities and angular distribution of gamma rays attributed to 140Ce have been measured. In addition to verifying known level characteristics, a spin assignment Jpi =4+ was found for the 2515.8 keV level. The existence of levels at 2628.9, 3001.3, 3395.7 and 3473.8 keV excitation energy was confirmed. Multipole mixing ratios have been extracted for nine of the most intense gamma -ray transitions. The experimental level energies and several electromagnetic properties are compared with shell-model predictions.

Program Summary

The angular distributions of gamma rays following inelastic neutron scattering near threshold to the first excited states of the target nuclei were investigated experimentally and theoretically.Measurements used NaI(Tl) crystal detectors and natural targets of iron and cerium. Data were obtained for the angular distribution of gamma rays following inelastic neutron scattering by 56Fe at the neutron center-of-mass energies E = 0.87, 0.90, 0.93, 0.95 and 0.99 MeV and by 140Ce at E = 1.64, 1.67, 1.71, 1.75 and 1.87 MeV.The predictions for the gamma-ray angular distributions of the two following theories are determined: (i) the Satchler-Scheldon theory and (ii) the theory of Moldauer, specialized to the pure compound nucleus process and employing the “uncorrelated amplitude” assumption. Near threshold the predictions of the two theories are nearly the same.Theory and experiment are in good agreement for cerium at all energies at which angular distributions were obtained and for iron at E = 0.99 MeV but not at lower energies.Two general conclusions are drawn about measurements of the angular distribution of gamma rays following inelastic neutron scattering in medium and heavy nuclei at energies near threshold; (i) such measurements are not useful in deciding between the theories of Satchler-Sheldon and Moldauer, but (ii) they provide data for a sensitive test of the Hauser-Feshbach statistical assumptions.

Fragmented g9/2isobaric analogue resonance in the52Cr(p, )53Mn reaction

Resonance consistent with fragmented g9/2 analogue resonances have been found in 53Mn corresponding to the Ex=3.715 MeV level in the 53Cr parent nucleus. The resonance was located through the 53Cr(p, gamma )53Mn reaction. Total gamma spectra were measured with a Ge(Li) detector in 2 keV steps in the expected proton energy range. Excitation functions for the different primary transitions were constructed. The g9/2 IAR was found with nine components at Ep=4115, 4134, 4140, 4157, 4165, 4176, 4182, 4188 and 4197 keV. The angular distribution of gamma rays was measured on the five strongest resonances, which were suggested to have spin and parity Jpi =9/2+ based on the gamma excitation functions, branching ratios and angular distributions. The absolute gamma transition strength distribution was fitted with a strength function. The position of the IAR, Ea, the spreading width Gamma s, and the analogue-halfway coupling matrix element were determined from the fit. The Gamma gamma 0 transition strength for the IAR was determined to be gamma gamma 0=21 eV.