Gamma-ray Angular Distributions Research Articles

Gamma spectroscopy of even-even Ytterbium isotopes

The even-even Ytterbium isotopes lack spectroscopic information with the increase of the neutron number and they are well deformed nuclei, presenting rotational properties. In this mass region of the nuclear chart predictions have shown rare phenomena related to nuclear structure, such as shape coexistence. In this work the population of excited states were investigated in the even-even Yb isotopes via the 2n-transfer reaction 168-174Yb (18O, 16O) 170-176Yb. The measurements were carried out at the 9 MV Tandem accelerator at the Horia Hulubei National Institute of Physics and Nuclear Engineering (IFIN-HH) in Romania. The deduced gamma-ray angular distributions in the ground state bands are found to correspond with transitions, as expected

Angular distribution of $$\gamma $$ rays emitted by oriented nuclei: the case of $$^{92}$$Mo formed in the reaction $$^6$$Li+$$^{89}$$Y

Gamma-ray angular distributions in oriented $$^{92}$$ Mo produced via the $$^{6}$$ Li+ $$^{89}$$ Y reaction were studied in this work. The characteristic $$\gamma $$ rays in $$^{92}$$ Mo were measured by means of the GALILEO array, which is composed of 25 Compton-suppressed HPGe detectors arranged in a nearly 2 $$\pi $$ geometry. A detailed analysis of the spin-alignment attenuation factors ( $$\alpha _2$$ ) for different excited states in $$^{92}$$ Mo was performed, by analyzing the measured angular distribution coefficients of several pure-E2 transitions. The relationship between $$\alpha _2$$ and the spin was established in $$^{92}$$ Mo and the 244-keV transition between the 5 $$^-_1$$ and 4 $$^+_1$$ states resulted to have a E1 + M2 character with a mixing ratio ( $$\delta $$ ) of $$-0.05^{+0.05}_{-0.06}$$ , consistent with shell model calculations.

Precise resonance energies measured for energy calibration of particle accelerator using thin silicon–nitride foils

In this work resonance parameters of the 28Si(p,p′γ)28Si (Eγ = 1779 keV) and 14N(p,p′γ)14N (Eγ = 2313 keV) reactions were measured between 3 and 4 MeV proton energies for absolute proton beam energy calibration of particle accelerators. For the measurements commercially available self-supporting thin silicon–nitride films and a HPGe gamma-detector were used which are readily available in most accelerator laboratories. Based on our measurement and on the assessment of literature data, the following resonance energies and widths are recommended: 3100.6 ± 0.9 keV (Γ = 11.9 ± 0.4 keV) and 3338.1 ± 1.0 keV (Γ = 11.0 ± 0.5 keV) in 28Si(p,p′γ)28Si and 3903.1 ± 1.7 keV (Γ = 98 ± 1 keV) and 3991.6 ± 1.1 keV (Γ = 10.8 ± 0.5 keV) in 14N(p,p′γ)14N. In addition to the resonance measurements, absolute thick target yields and gamma-ray angular distributions were measured for the 28Si(p,p′γ)28Si (Eγ = 1779 keV) reaction in the vicinity of Ep = 3.10 and 3.34 MeV for ion beam analysis purposes using a thick silicon wafer target.

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.

Shape and angular distribution of the 4.439-MeV γ -ray line from proton inelastic scattering off C12

The emission of the 4.438-MeV gamma-ray line in proton inelastic scattering off 12C has been investigated in detail. For this, two independent descriptions of the correlated scattering and emission process have been developed, one for the direct reaction mechanism and the other for the compound-nucleus (CN) component. Direct reactions were calculated in the framework of the coupled-channels formalism, while the CN component was described as a superposition of separate resonances with definite spin and parity, treated with the angular momentum coupling theory. Both components were incoherently added and compared to a comprehensive data set on measured line shapes and gamma-ray angular distributions in the proton energy range Ep = 5.44 - 25.0 MeV. In the range Ep ~ 14 - 25 MeV, good agreement with data was obtained with a dominating direct reaction component. At lower energy, an important CN component was required to describe line shape and angular distribution data. In general, a good decription of the data could be found for a CN component with spin and parity corresponding to a known nearby resonance. The new calculation improves significantly the agreement with line shape data compared to previous ones. Based on these results, predictions for line shapes and gamma-ray angular distributions up to Ep = 100 MeV were made and applied to gamma-ray emissions in solar flares and proton radiotherapy.

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.

Measurement of Angular Distributions of Gamma Rays from the Inelastic Scattering of 14.1-MeV Neutrons by Carbon and Oxygen Nuclei

The results obtained by measuring the angular and energy distributions of gamma rays originating from the inelastic scattering of 14.1-MeV neutrons by carbon and oxygen nuclei are presented. The measurements in question were performed by the tagged-neutron method in a beam of an ING-27 standard portable neutron generator. The angular distributions of gamma rays emitted by the 2+ state of 12С at 4.43 MeVand the 3− state of 16O at 6.13 MeV were obtained.

Studying collective nuclear excitations with fast neutrons: a comparison of 76Ge and 76Se

The low-lying, low-spin level structures of 76Ge and 76Se were studied with the (n,n'γ) reaction. Gamma-ray excitation function and angular distribution measurements were performed, and level spins, level lifetimes, γ-ray intensities, and multipole mixing ratios were determined. Large observed B(E2) values support the identification of low-lying band structures.

Level structure of 164Dy from the (n, n′γ) reaction

By employing a beam of reactor fast neutrons, gamma-ray spectra and angular distributions of gamma rays with respect to the neutron-beam axis were measured in the reaction 164Dy(n, n′γ). The scheme of levels and gamma transitions in 164Dy was composed on the basis of data published earlier and new levels, rotational bands, gamma transitions, and multipole-mixing parameters. It is concluded that the scheme of J = 0–4 levels is complete up to the excitation energy of 1.95 MeV. The commonly accepted rule in constructing K n π = 02 + and 11 + rotational bands is found to be violated. The nature of the 2+ level at the energy of 1796.68 keV is discussed.

Improvements in the PIGE technique via gamma-ray angular distribution

Particle induced gamma-ray emission (PIGE) is an ion beam technique used for isotopic elemental analysis of materials, based on gamma-ray spectroscopy. In the traditional PIGE setup, the gamma-ray detector is positioned at the neutral angles 55° or 125° with respect to the beam direction in order to measure gamma-rays with different angular distributions. Although these angles permit measurements without an a-priori knowledge of the specific angular distributions, this choice is not efficient if one wants to identify a specific element since a longer acquisition time is needed.In this work, we propose to optimize the PIGE measurements by choosing the detector angle position due to the previous knowledge of the gamma-ray multipolarity and the nuclear reaction. We present the angular distribution calculations for the isotopes most frequently identified by PIGE analysis, specially in Cultural Heritage objects. Calculations demonstrate that a gain in the intensity up to 70% can be achieved allowing the elemental identification in shorter times. This result is promising and represents a more efficient alternative to perform PIGE measurements.

Measurement of gamma-ray production cross sections for nuclear reactions 14N(d,pγ)15N and 28Si(d,pγ)29Si

In this work the differential cross sections for gamma-ray emission from the 14N(d,pγ)15N (Eγ=1885, 2297, 7299 and 8310keV) and from the 28Si(d,pγ)29Si (Eγ=1273, 2028, 2426 and 4934keV) were measured simultaneously with the 14N(d,p4,5,6,7)15N differential cross sections and 14N(d,d)14N elastic scattering cross section using a HPGe detector at 55° and an ion implanted Si detector at 135° with respect to the beam direction in the deuteron energy range 0.65–2.0MeV. The target was a thin silicon-nitride film. Gamma-ray angular distribution measurements were performed to determine the possible anisotropy of the gamma-ray emission, and the measured cross section values were converted into total gamma-ray producing cross sections for most of the gamma-ray emissions. The average uncertainties of nitrogen and silicon gamma-ray production cross sections are 5% and 12%, respectively and 8% concerning the particle production cross section of natN(d,d0)natN and 14N(d,p4,5,6,7)15N reactions.

Ambiguities in the rate of oxygen formation during stellar helium burning in the12C(α,γ) reaction

The rate of oxygen formation determines the C/O ratio during stellar helium burning. It is the single most important nuclear input of stellar evolution theory including the evolution of Type II and Type Ia supernova. Yet the low energy cross section of the fusion of 4He + 12C denoted as the 12C(a,g)16O reaction still remains uncertain after forty years of extensive work. We analyze and critically review the most recent measurements of complete angular distributions of the outgoing gamma-rays at very low energies (Ecm > 1.0 MeV). Our analysis of the angular distribution measured with the EUROGAM/GANDI arrays lead us to conclude considerably larger error bars than published hence they are excluded from the current sample of "world data". We show that the current sample of "world data" of the measured E2 cross section factors below 1.7 MeV cluster to two distinct groups that lead to two distinct extrapolations of SE2(300) ~ 60 or ~ 154 keVb. We point to a much neglected discrepancy between the measured E1-E2 phase difference (phi_12) and unitarity as required by the Watson theorem, suggesting systematic problem(s) of some of the measured gamma-ray angular distributions. The ambiguity of the extrapolated SE2(300) together with a previously observed ambiguity of SE1(300) represent the current state of the art of the field and they must be resolved by future measurements of complete and detailed angular distributions of the 12C(a,g) reaction at very low energies (Ecm < 1.0 MeV).

Nuclear structure of30S and its implications for nucleosynthesis in classical novae

The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. To investigate the level structure of 30S above the proton threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam gamma-ray spectroscopy experiments were performed. Differential cross sections of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born approximation calculations were performed to constrain the spin-parity assignments of the observed levels. An energy level scheme was deduced from gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction. Spin-parity assignments based on measurements of gamma-ray angular distributions and gamma-gamma directional correlation from oriented nuclei were made for most of the observed levels of 30S. As a result, the resonance energies corresponding to the excited states in 4.5 MeV - 6 MeV region, including the two astrophysically important states predicted previously, are measured with significantly better precision than before. The uncertainty in the rate of the 29P(p,gamma)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via 1D hydrodynamic nova simulations.

Investigation of γ radiation from 178Hf in the respective (n, n′γ) reaction

The spectra and angular distributions of gamma rays were measured in the reaction 178Hf(n, n′γ) induced by a beam of fast reactor neutrons. Data onmultipole mixtures in gamma transitions and a lot of new information about gamma transitions of energy 1.5 to 3.0 MeV were obtained. A comparison of these results with information known from the respective (n, γ) reaction made it possible to refine the schemes of deexcitation of 178Hf levels at energies above 1.5 MeV, to determine more precisely features of these levels, and to introduce new levels and rotation bands at excitation energies of about 2MeV.

Development and Evaluation of a Fast Calculation Method for Gamma Ray Skyshine Dose Using Data Libraries

A fast calculation method for gamma ray skyshine dose was developed. Four data libraries including anisotropy factors and buildup factors in the gamma ray transport calculation in air and the buildup flux energy spectrum and edge correction factor in the calculation of the precise energy spectrum of gamma ray flux penetrating through the upper shields were used. The anisotropy factors were generated on the basis of line beam response functions obtained by Hirayama et al. using the EGS4 code. The other three data libraries were generated by the invariant embedding method. Multilayer shields and angular distributions of gamma rays from sources were assumed to have a rotational symmetry with respect to the center axis of the shields along which the sources were located. Accuracy of the method was evaluated through comparison with the measured dose in the skyshine benchmark experiment and doses calculated by other dependable methods. It was found that the present method could simulate the measured dose with a discrepancy of 50% or less, and that transport of gamma rays in air due to a conical beam could be solved within an error of about 10–20%, except for the cases in which the beam angle lies in the range < 10 deg. The present method has two advantageous features: the skyshine dose can be obtained very quickly and very easily by general users.

Multipole mixtures in gamma transitions from the reaction 92Mo(n, n′γ)

Angular distributions of gamma rays from the reaction 92Mo(n,n′γ) with respect to the axis of the fast-reactor-neutron beam were measured. The known scheme of levels and gamma transitions in 92Mo was supplemented. The multipole-mixture parameters δ were found for gamma transitions between levels. The relationship between the parameters δ and the structure of excited states of 92Mo is discussed.

On the K π = 0+ rotational bands in the 178Hf nucleus

The results obtained by studying the angular distributions of gamma rays with respect to the neutron-beam axis in the reaction 178Hf(n, n′γ) involving the deexcitation of the Kπ = 0+ rotational bands of 178Hf are presented.New information about themultipole-mixing parameter δ in gamma transitions from the levels of these bands is obtained. The Kπ = 04+ band is constructed anew. The relationship between the parameter δ for the (2+0n−2+01) gamma transition and the energy gap Δn = Elev(2+0n) − Elev(0+0n), on one hand, and the quasiparticle structure of the rotational band, on the other hand, is discussed for 178Hf on the basis of the quasiparticle-phonon model.

Mechanisms of excitation of T-odd correlations for prescission gamma rays and structure of these correlations

Conditions for the appearance and observation of prescission gamma rays emitted by a fissioning nucleus prior to its separation into fission fragments were investigated within quantum-mechanical fission theory. It is shown that these conditions are realizable in the gamma decay of isovector electric giant dipole resonances in a fissile nucleus that are excited because of nonadiabaticity of the collective deformation motion of the nucleus at the ultimate stages of its prefission evolution. Angular and energy distributions of prescission gamma rays emitted by unpolarized fissioning nuclei are analyzed. Features of T-odd correlations in angular distributions of gamma rays arising in the fission of unpolarized target nuclei that is induced by polarized cold neutrons are investigated, and it is shown that these correlations are similar in nature to T-odd ROT correlations discovered earlier for alpha particles emitted in the ternary fission of nuclei.

Investigation of 88Sr in the reaction Sr(n, n′γ)

With the aid of a beam of fast reactor neutrons, the gamma-ray spectrum and angular distributions of gamma rays with respect to the neutron-beam axis are measured in the reaction Sr(n, n′γ) along with the lifetimes of 88Sr levels. Values of the multipole-mixture parameter δ are found for gamma transitions between levels.

Determination of the21+→01+transition strengths inNi58andNi60

Gamma-ray angular distribution measurements following the ${}^{\mathrm{nat}}$Ni($n,{n}^{'}\ensuremath{\gamma}$) reaction were carried out at 1.6 and 1.8 MeV neutron energies. Through the Doppler-shift attenuation method, the lifetime of the ${2}_{1}^{+}$ state in $^{58}\mathrm{Ni}$ is determined as $\ensuremath{\tau}=1.{00}_{\ensuremath{-}0.10}^{+0.15}$ ps, which yields a $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value of $9.{4}_{\ensuremath{-}1.2}^{+1.0}$ W.u. From previous measurements and this work, average values of $\ensuremath{\tau}=0.94(3)$ ps and $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})=10.0(4)$ W.u. are recommended as standards for normalization. In addition, a longer lifetime of $\ensuremath{\tau}=1.{30}_{\ensuremath{-}0.20}^{+0.30}$ ps has been determined for the ${2}_{1}^{+}$ state in $^{60}\mathrm{Ni}$, which yields an $E2$ strength of $10.{7}_{\ensuremath{-}2.5}^{+1.7}$ W.u. Our results support an enhancement of proton-core excitations and related quadrupole and pairing strengths in the light Ni isotopes, in agreement with mean-field and shell-model calculations.