Gamma-ray Strength Functions Research Articles

Nuclear properties for nuclear astrophysics studies

The need for nuclear data for astrophysics applications challenges experimental techniques as well as the robustness and predictive power of present nuclear models. Most of the nuclear data evaluations and predictions are still performed on the basis of phenomenological nuclear models. In the last decades, important progress has been achieved in fundamental nuclear physics, making it now feasible to use more reliable, but also more complex microscopic or semi-microscopic models in the evaluation and prediction of nuclear data for practical applications. In the present contribution, the reliability and accuracy of recent nuclear theories are discussed for most of the quantities needed to estimate reaction cross sections and beta-decay rates, namely nuclear masses, nuclear level densities, gamma-ray strength, fission properties and beta-strength functions. It is shown that nowadays, mean-field models can be tuned at the same level of accuracy as the phenomenological models, renormalized on experimental data if needed, and therefore can replace the phenomenological inputs in the prediction of nuclear data. While fundamental nuclear physicists keep on improving state-of-the-art models, in particular the shell or ab-initio models, nuclear applications could make use of their most recent results as quantitative constraints or guides to improve the predictions in energy or mass domain that will remain inaccessible experimentally.

Evolution of the γ -ray strength function in neodymium isotopes

The experimental gamma-ray strength functions (gamma-SFs) of 142,144-151Nd have been studied for gamma-ray energies up to the neutron separation energy. The results represent a unique set of gamma-SFs for an isotopic chain with increasing nuclear deformation. The data reveal how the low-energy enhancement, the scissors mode and the pygmy dipole resonance evolve with nuclear deformation and mass number. The data indicate that the mechanisms behind the low-energy enhancement and the scissors mode are decoupled from each other.

Astrophysical $$\boldsymbol{S}$$-Factor Calculations under the Effects of Gamma-Ray Strength Functions for Some Alpha Capture Reactions

The reaction cross section and the energy, at which this value is obtained, are extremely important parameters in the calculation of astrophysical $$S$$ -factor. Astrophysical $$S$$ -factor values can be shown as one of the most notable values not only for nuclear reactions occurring at low energies but also for deeper understanding of astrophysical processes too. Considering the importance of this variable, it has been made possible to calculate it with theoretical methods when it cannot be measured experimentally. Theoretical calculations require the energy and the reaction cross section values. While the reaction cross section value, which can be explained as the probability of occurrence of a reaction, is obtained by theoretical calculations, the result can be affected by many parameters. In this study, it is aimed to investigate the effects of gamma-ray strength functions on the calculations of the astrophysical $$S$$ -factor values of $${}^{96}$$ Ru( $$\alpha$$ , $$\gamma$$ ) $${}^{100}$$ Pd, $${}^{106}$$ Cd( $$\alpha$$ , $$\gamma$$ ) $${}^{110}$$ Sn, $${}^{112}$$ Sn( $$\alpha$$ , $$\gamma$$ ) $${}^{116}$$ Te, $${}^{113}$$ In( $$\alpha$$ , $$\gamma$$ ) $${}^{117}$$ Sb, and $${}^{144}$$ Sm( $$\alpha$$ , $$\gamma$$ ) $${}^{148}$$ Gd reactions by using the cross section values obtained via utilizing different gamma-ray strength functions, which is one of the parameters known to have an effect on the cross section calculations. All calculation results were obtained using a well-known computation code TALYS, and the data obtained were analysed both graphically and statistically against available experimental data from the Experimental Nuclear Reaction Data (EXFOR) Library.

The comparison of theoretical model calculations and experimental data of 58,60,61,64Ni, 64,66,68Zn, and 63,65Cu photo-nuclear reactions

Photonuclear reactions cross-sections using TALYS 1.95 code in the GDR region were studied to test the reliability of various models of gamma ray strength functions. Six different gamma ray strength function models have been applied. The photo-neutron reactions for the isotopes 58,60,61,64Ni, 63,65Cu, and 64,66,68Zn were investigated. The theoretical results were compared with the experimental data from the EXFOR data library. A relative variance analysis has performed to choose the gamma strength function mode which describes the experimental data the best.

Evaluation of gamma-ray strength function based on measured gamma-ray pulse-height spectra in time-of-flight neutron capture experiments

In order to develop an evaluation method of gamma-ray strength function (GSF), neutron capture pulse-height (PH) spectrum of gold was employed, where it was measured with the NaI(Tl) spectrometer of AN-NRI installed at the Material and Life Science Experimental Facility in J-PARC. The neutron capture gamma-ray spectrum of gold was calculated using the nuclear reaction model code CCONE. In order to obtain the information on GSF from the measured data, a gamma-ray response function for the NaI(Tl) spectrometer was calculated by the Monte-Carlo particle-transport simulation code PHITS. As a result, the PH spectrum comparable with measured one was derived by applying the gamma-ray response function to the calculated gamma-ray spectrum. By evaluation with measured PH spectra, we obtained GSF which reasonably explains measured PH spectrum in the continuum region.

Theoretical photoneutron cross-section calculations on Osmium isotopes by Talys and Empire codes

In this study, the level density parameter and the gamma ray strength function effects on photoneutron reaction cross-section calculations for Osmium isotopes were investigated by employing available level density models and gamma ray strength functions within Talys v1.8 and Empire v3.1 nuclear codes. A relative variance analysis was done to determine the best gamma ray strength function. Then, the effect of level density models for the photoneutron reactions was investigated by using the best gamma ray strength function. The results were compared with each other and also with the experimental data taken from the literature.

Role of consistent parameter sets in an assessment of the α -particle optical potential below the Coulomb barrier

Background: Further studies of high-precision measurements of alpha-induced reaction data below the Coulomb barrier have still raised questions about the alpha-particle optical model potential (OMP) within various mass ranges, i.e. for 64Zn, 108Cd, 113,115In, 121,123Sb, and 191,193Ir target nuclei. Purpose: The accuracy as well as eventual uncertainties and/or systematic errors of using a previous optical potential are much better considered by analysis of such accurate data. Method: Statistical model (SM) calculations of the (alpha,x) reaction cross sections have been carried out using model parameters which were previously obtained by analyzing independent data, particularly gamma-ray strength functions, and taking into account their uncertainties and questions of extrapolation for nuclei without similar data. Results: Consistent description of the recent alpha-induced reaction data is provided by the above-mentioned optical potential with no empirical rescaling factors of either its own parameters or the gamma and/or nucleon widths. Effects of still uncertain SM parameters on calculated alpha-induced reaction cross sections and conclusions on the alpha-OMP can be now discussed due to unprecedented precision of the new data. Conclusions: The alpha-particle optical potential has been confirmed at incident energies below the Coulomb barrier using statistical-model parameters validated through a former analysis of independent data.

An investigation of effects of level density models and gamma ray strength functions on cross-section calculations for the production of 90Y, 153Sm, 169Er, 177Lu and 186Re therapeutic radioisotopes via (n,γ) reactions

Abstract One of the methods used to treat different cancer diseases is the employment of therapeutic radioisotopes. Therefore, many clinical, theoretical and experimental studies are being carried out on those radioisotopes. In this study, the effects of level density models and gamma ray strength functions on the theoretical production cross-section calculations for the therapeutic radioisotopes 90Y, 153Sm, 169Er, 177Lu and 186Re in the (n,γ) route have been investigated. TALYS 1.9 code has been used by employing different level density models and gamma ray strength functions. The theoretically obtained data were compared with the experimental data taken from the literature. The results are presented graphically for better interpretation.

Average cross section measurement for 162Er(γ,n) reaction compared with theoretical calculations using TALYS

Bremsstrahlung photon beam delivered by a linear electron accelerator has been used to experimentally determine the near threshold photonuclear cross section data of nuclides. For the first time, (γ,n) cross section data was obtained for the astrophysical important nucleus 162Er. Moreover, theoretical calculations have been applied using the TALYS 1.6 code. The effect of the gamma ray strength function on the cross section calculations has been studied. A satisfactorily reproduction of the available experimental data of photonuclear cross section at the energy region below 20 MeV could be achieved. The photon flux was monitored by measuring the photons yield from seven well known (γ, n) reactions from the threshold energy of each reaction up to the end-point energy of the photon beam used. An integrated cross-section 87 ± 14 mb is calculated for the photonuclear reaction 162Er(γ,n) at the energy 9.2 - 14 MeV. The effective cross section estimated using the TALYS code range between 89 and 96 mb depending on the γ-strength function used. The result for 162Er(γ,n), is found to be in good agreement with the theoretical values obtained by TALYS 1.6. So, the present indirect process could be a valuable tool to estimate the effective cross section of (γ,n) reaction for various isotopes using bremsstrahlung beams.

Quasiparticle random phase approximation predictions of the gamma-ray strength functions using the Gogny force

Dipole excitations of nuclei are crucial since they play an important role in nuclear reaction modeling in connection with the photoabsorption and the radiative capture processes. We present here results for the gamma-ray strength function obtained in large-scale axially-symmetric deformed quasiparticle (qp) random phase approximations approach using the finite-range Gogny force, with a particular emphasis on the E1 mode. The convergence with respect to the number of harmonic oscillator shells adopted and the cut-off introduced in the 2-quasiparticle excitation energy space is analyzed. The microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA (HFB+QRPA) calculation has unfortunately to be broken, some phenomenological corrections being needed to take into account effects beyond the standard 2-qp QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. The corresponding phenomenological parameters are adjusted on experimental photoabsorption data. In such a procedure, a rather satisfactory description of experimental data is obtained. To study the sensitivity of these phenomenological corrections on the extrapolation, both at low energies and towards exotic neutron-rich nuclei, three different prescriptions are considered. They are shown to lead to rather similar predictions of the E1 strength at low energies as well as for exotic neutron-rich nuclei. The Gogny-HFB+QRPA strength is finally applied to the calculation of radiative neutron capture cross sections and the predictions compared with those obtained with more traditional Lorentzian-type approaches.

Nuclear level densities and gamma-ray strength functions of 145,149,151Nd isotopes

The nuclear level densities and gamma-ray strength functions are the key elements for Hauser-Feshbach statistical model calculations to predict reaction cross sections which have many applications including astrophysics. The nuclear level densities and y-ray strength functions have been determined for 145,149,151Nd isotopes below the neutron separation energies using the Oslo method with the 144,148,150Nd(d,p) reactions. The results from the first measurements as well as planned experiments at OCL will be presented.

Average cross section measurement for 162Er (γ, n) reaction compared with theoretical calculations using TALYS

Bremsstrahlung photon beam delivered by a linear electron accelerator has been used to experimentally determine the near threshold photonuclear cross section data of nuclides. For the first time, (γ, n) cross section data was obtained for the astrophysical important nucleus 162Er. Moreover, theoretical calculations have been applied using the TALYS 1.6 code. The effect of the gamma ray strength function on the cross section calculations has been studied. A satisfactorily reproduction of the available experimental data of photonuclear cross section at the energy region below 20 MeV could be achieved. The photon flux was monitored by measuring the photons yield from seven well known (γ, n) reactions from the threshold energy of each reaction up to the end-point energy of the photon beam used. An integrated cross-section 87±14 mb is calculated for the photonuclear reaction 162Er (γ, n) at the energy 9.2–14 MeV. The effective cross section estimated using the TALYS code range between 89 and 96 mb depending on the γ-strength function used. To validate the method for the estimation of the average cross-section data of 162Er (γ, n) reaction, the same procedure has been performed to calculate the average cross-section data of 197Au (γ, n) and 55Mn (γ, n) reactions. In this case, the photons yield from the rest well known (γ, n) reactions was used in order to monitoring the photon flux. The results for 162Er (γ, n), 197Au (γ, n) and 55Mn (γ, n) are found to be in good agreement with the theoretical values obtained by TALYS 1.6. So, the present indirect process could be a valuable tool to estimate the effective cross section of (γ, n) reaction for various isotopes using bremsstrahlung beams.

Analysis of uncertainties inα-particle optical-potential assessment below the Coulomb barrier

Background: Recent high-precision measurements of alpha-induced reaction data below the Coulomb barrier have pointed out questions of the alpha-particle optical-model potential (OMP) which are yet open within various mass ranges. Purpose: The applicability of a previous optical potential and eventual uncertainties and/or systematic errors of the OMP assessment at low energies can be further considered on this basis. Method: Nuclear model parameters based on the analysis of recent independent data, particularly gamma-ray strength functions, have been involved within statistical model calculation of the (alpha,x) reaction cross sections. Results: The above-mentioned potential provides a consistent description of the recent alpha-induced reaction data with no empirical rescaling factors of the and/or nucleon widths. Conclusions: A suitable assessment of alpha-particle optical potential below the Coulomb barrier should involve the statistical-model parameters beyond this potential on the basis of a former analysis of independent data.

Determination of the electric dipole (E1) gamma ray strength function of 56Mn from the Bn level to low levels by two-step gamma cascades

Investigation of gamma ray strength function is necessary to determine some nuclear characteristics, such as: spin, parity, electromagnetic transitions, cross section, … In this research, 55Mn target was activated on the neutron of 3rd horizontal channel of Dalat nuclear reactor. The experimental data was collected by event-event coincidence by gammagamma coincidence system. The 56Mn deexcitation afforded the collected of 49 gamma – gamma twostep cascades. This was applied on shell model to determine the spin, parity, electric dipole gamma strength function (E1) as well as comparing between the theoretical and experimental E1 transition probabilities

Statistical properties ofPu243, andPu242(n,γ)cross section calculation

The level density and gamma-ray strength function (gammaSF) of 243Pu have been measured in the quasi-continuum using the Oslo method. Excited states in 243Pu were populated using the 242Pu(d,p) reaction. The level density closely follows the constant-temperature level density formula for excitation energies above the pairing gap. The gammaSF displays a double-humped resonance at low energy as also seen in previous investigations of actinide isotopes. The structure is interpreted as the scissors resonance and has a centroid of omega_{SR}=2.42(5)MeV and a total strength of B_{SR}=10.1(15)mu_N^2, which is in excellent agreement with sum-rule estimates. The measured level density and gammaSF were used to calculate the 242Pu(n,gamma) cross section in a neutron energy range for which there were previously no measured data.

Large-scale deformed QRPA calculations of the gamma-ray strength function based on a Gogny force

The dipole excitations of nuclei play an important role in nuclear astrophysics processes in connection with the photoabsorption and the radiative neutron capture that take place in stellar environment. We present here the results of a large-scale axially-symmetric deformed QRPA calculation of the γ-ray strength function based on the finite-range Gogny force. The newly determined γ-ray strength is compared with experimental photoabsorption data for spherical as well as deformed nuclei. Predictions of γ-ray strength functions and Maxwellian-averaged neutron capture rates for Sn isotopes are also discussed.

Towards more accurate and reliable predictions for nuclear applications

The need for nuclear data far from the valley of stability, for applications such as nuclear astrophysics or future nuclear facilities, challenges the robustness as well as the predictive power of present nuclear models. Most of the nuclear data evaluation and prediction are still performed on the basis of phenomenological nuclear models. For the last decades, important progress has been achieved in fundamental nuclear physics, making it now feasible to use more reliable, but also more complex microscopic or semi-microscopic models in the evaluation and prediction of nuclear data for practical applications. In the present contribution, the reliability and accuracy of recent nuclear theories are discussed for most of the relevant quantities needed to estimate reaction cross sections and beta-decay rates, namely nuclear masses, nuclear level densities, gamma-ray strength, fission properties and beta-strength functions. It is shown that nowadays, mean-field models can be tuned at the same level of accuracy as the phenomenological models, renormalized on experimental data if needed, and therefore can replace the phenomenogical inputs in the prediction of nuclear data. While fundamental nuclear physicists keep on improving state-of-the-art models, e.g. within the shell model or ab initio models, nuclear applications could make use of their most recent results as quantitative constraints or guides to improve the predictions in energy or mass domain that will remain inaccessible experimentally.

Theoretical Analysis of Gamma-ray Strength Function for Pd Isotopes

Gamma-ray strength functions of Pd isotopes were investigated by using measured photonuclear reaction cross sections and neutron capture reaction data. The present results calculated by nuclear reaction calculation code CCONE well reproduce the available experimental data. It is found from the evaluation of capture γ-ray spectra that additional resonances with a variety of strength are present at around γ-ray energies of 5 to 6 MeV. The calculated values of s-wave γ strength function for 106,108Pd are 40% smaller than compiled values derived from resolved resonance data.

Scissors resonance in the quasicontinuum of Th, Pa, and U isotopes

The gamma-ray strength function in the quasi-continuum has been measured for 231-233Th, 232,233Pa and 237-239U using the Oslo method. All eight nuclei show a pronounced increase in gamma strength at omega_SR approx 2.4 MeV, which is interpreted as the low-energy M1 scissors resonance (SR). The total strength is found to be B_SR = 9-11 mu_N^2 when integrated over the 1 - 4 MeV gamma-energy region. The SR displays a double-hump structure that is theoretically not understood. Our results are compared with data from (gamma, gamma') experiments and theoretical sum-rule estimates for a nuclear rigid-body moment of inertia.

Evaluation of neutron nuclear data for erbium

Neutron nuclear data on 162,164,166,167,168.170Er have been evaluated for the next version of JENDL general purpose file in the energy region from 10−5 eV to 20 MeV. The resolved resonance parameters remain unchanged from JENDL-4.0, while the unresolved resonance parameters were revised. The statistical model was applied to calculate the cross sections above the resolved resonance region. In the calculations, coupled-channel optical model parameters were used for neutrons. Pre-equilibrium and direct-reaction processes were taken into account in addition to the compound process. A modified Lorentzian was employed for E1 gamma-ray strength functions. The present evaluation is consistent with available experimental data. The evaluated data are compiled into an ENDF-formatted data file.