Γ-ray Production Cross Sections Research Articles

New γ-ray production cross sections for the 4.439 and 6.129 MeV lines of 12C and 16O. Astrophysical implications

Gamma-ray line production cross sections from nuclear reactions induced by 30 - 200 MeV protons on natC and Mylar targets have been measured at the SSC facility of iThemba LABS. Results for the 4.439 and 6.129 MeV prominent lines of 12C and 16O of astrophysical concern are reported and discussed.

γ-ray emission in proton-induced nuclear reactions on [formula omitted]C and Mylar targets over the incident energy range, Ep = 30 – 200 MeV. Astrophysical implications

We have measured the γ-ray line production cross sections in proton-induced nuclear reactions on various target nuclei (12C, 16O, 24Mg, 28Si, 56Fe) of chemical elements abundant in astrophysical sites (solar flares, the interstellar medium, cosmic compact objects) over the incident energy range of Ep = 30 – 200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 separated sector cyclotron of iThemba LABS using a high-energy resolution, high-efficiency detection array composed of 8 Compton-suppressed clover detectors comprising 32 HP-Ge crystals for recording the γ-ray energy spectra. In the current paper, we focus on γ-ray de-excitation lines produced in proton irradiations of natC and Mylar targets, in particular, on the prominent 4.439 and 6.129 MeV lines of 12C and 16O which are among the strongest lines emitted in solar flares and in interactions of low-energy cosmic rays (LECRs) with the gas and dust of the inner galaxy. We report new γ-ray production experimental cross section data for ten nuclear γ-ray lines that we compare to previous low-energy data sets from the literature, to the predictions of the TALYS code of nuclear reactions and to a semi-empirical compilation. In the first approach, performing calculations with default input parameters of TALYS we observed substantial deviations between the predicted cross sections and experimental data. Then, using modified optical model potential (OMP) and nuclear level deformation parameters as input data we generated theoretical excitation functions for the above two main lines fully consistent with experimental data. In contrast, the experimental data sets for the other eight analyzed lines from the two proton-irradiated targets exhibit significant deviations with the predicted cross section values. We also report line-shape experimental data for the line complex observed at Eγ = 4.44 MeV in irradiations of the two targets. Finally, we emphasize the astrophysical implications of our results.

Templates of expected measurement uncertainties for (n, xn) cross sections

A template is provided for evaluating experimental uncertainties for neutron elastic and inelastic scattering cross sections andγ-ray production cross sections from (n, xn) measurements at laboratories with monoenergetic or white neutron sources. A typical range of uncertainties is presented for experiments detecting the scattered neutrons or the resulting de-excitationγrays based on a survey of available data and input from many experimentalists and theorists with extensive knowledge in the field. Models commonly used to evaluate the resulting cross-sections are also discussed. Suggestions are made regarding what experimental and uncertainty information is needed for data evaluations and should be included when reporting experimental (n, xn) cross sections. Uncertainty values and correlations are recommended if these values cannot be estimated for past data from the literature.

Neutron elastic and inelastic cross section measurements on silicon from 0.8–8 MeV

Neutron elastic and inelastic scattering differential cross sections were measured at angles between 30∘ and 155∘ with incident neutron energies between 0.8 and 8 MeV. The measured differential scattering cross sections are compared to existing measurements and the ENDF/B-VIII.0, the JEFF-3.3, and the JENDL-4.0 data evaluations, as well as theoretical calculations from the TALYS-1.95 nuclear reaction code. Our results are reasonably well described by values from the ENDF/B-VIII.0 and JEFF-3.3 compilations. However, below 4 MeV, our backward-angle elastic scattering results tend to be lower than database/calculated values, suggesting that less recoil damage would occur than expected. Above 6 MeV, larger backward-angle cross sections are observed suggesting the opposite. Deexcitation γ rays produced in the inelastic scattering process were also studied for neutron energies between 1.9 and 4.5 MeV. Neutron inelastic scattering cross sections deduced from 28Si(n,nγ1) γ-ray production cross sections confirm our 28Si(n,n1) results. To the extent that data from GELINA and our experimental results can be compared, we have excellent agreement between the neutron inelastic scattering cross sections.

The calculation and evaluation for n+54,56,57,58Fe reactions

All cross sections of neutron-induced reactions, angular distributions, double differential cross sections, angle-integrated spectra, γ-ray production cross sections and energy spectra for 54,56,57,58 Fe are calculated by using theoretical models at incident neutron energies from 0.1 to 200 MeV. The present consistent theoretical calculated results are in good agreement with recent experimental data. The present evaluated data are compared with the existing experimental data and evaluated results from ENDF/B-VII, JENDL-4, JEFF-3, and the results are given in ENDF/B format.

Inspection of56Feγ-Ray angular distributions as a function of incident neutron energy using optical model approaches

Neutron inelastic scattering cross sections measured directly through (n,n) or deduced from γ-ray production cross sections following inelastic neutron scattering (n,n′ γ) are a focus of basic and applied research at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator). For nuclear data applications, angle-integrated cross sections are desired over a wide range of fast neutron energies. Several days of experimental beam time are required for a data set at each incident neutron energy, which limits the number of angular distributions that can be measured in a reasonable amount of time. Approximations can be employed to generate cross sections with a higher energy resolution, since at 125o , the a 2 P 2 term of the Legendre expansion is identically zero and the a 4 P 4 is assumed to be very small. Provided this assumption is true, a single measurement at 125o would produce the γ-ray production cross section. This project tests these assumptions and energy dependences using the codes CINDY/SCAT and TALYS/ECIS06/SCAT. It is found that care must be taken when interpreting γ-ray excitation functions as cross sections when the incident neutron energy is < 1000 keV above threshold or before the onset of feeding.

Inelastic neutron scattering cross-section measurements on 7Li and 63,65Cu

The γ-ray production cross section for the 477.6-keV transition in 7 Li following inelastic neutron scattering has been measured from the reaction threshold up to 18 MeV. This cross section is interesting as a possible standard for other inelastic scattering measurements. The experiment was conducted at the Geel Electron LINear Accelerator (GELINA) pulsed white neutron source with the Gamma Array for Inelastic Neutron Scattering (GAINS) spectrometer. Previous measurements of this cross section are reviewed and compared with our results. Recently, this cross section has also been calculated using the continuum discretized coupled-channels (CDCC) method. Experiments for studying neutrinoless double-β decay (2β0ν) or other very rare processes require greatly reducing the background radiation level (both intrinsic and external). Copper is a common shielding and structural material, used extensively in experiments such as COBRA, CUORE, EXO, GERDA, and MAJORANA. Understanding the background contribution arising from neutron interactions in Cu is important when searching for very weak experimental signals. Neutron inelastic scattering on nat Cu was investigated with GAINS. The results are compared with previous experimental data and evaluated nuclear data libraries.

Assessment of experimental d-PIGE γ-ray production cross sections for 12C, 14N and 16O and comparison with absolute thick target yields

Measured differential cross sections for deuteron induced γ-ray emission from the reactions 12C(d,pγ)13C, (Eγ=3089keV), 14N(d,pγ)15N (Eγ=8310keV) and 16O(d,pγ)17O (Eγ=871keV) available in the literature were assessed. In order to cross check the assessed γ-ray production cross section data, thick target γ-yields calculated from the differential cross sections were compared with available measured thick target yields. Recommended differential cross section data for each reaction were deduced for particle induced γ-ray emission (PIGE) applications.

Proton induced gamma-ray production cross sections and thick-target yields for boron, nitrogen and silicon

The excitation functions for the reactions 14N(p,p′γ)14N, 28Si(p,p′γ)28Si and 29Si(p,p′γ)29Si were measured at an angle of 55° by bombarding a thin Si3N4 target with protons in the energy range of 3.6–6.9MeV. The deduced γ-ray production cross section data is compared with available literature data relevant for ion beam analytical work. Thick-target γ-ray yields for boron, nitrogen and silicon were measured at 4.0, 4.5, 5.0, 5.5, 6.0 and 6.5MeV proton energies utilizing thick BN and Si3N4 targets. The measured yield values are put together with available yield data found in the literature. The experimental yield data has been used to cross-check the γ-ray production cross section values by comparing them with calculated thick-target yields deduced from the present and literature experimental excitation curves. All values were found to be in reasonable agreement taking into account the experimental uncertainties.

Determination of the effective sample thickness via radiative capture

A procedure for determining the effective thickness of non-uniform irregular-shaped samples via radiative capture is described. In this technique, partial γ-ray production cross sections of a compound nucleus produced in a neutron-capture reaction are measured using Prompt Gamma Activation Analysis and compared to their corresponding standardized absolute values. For the low-energy transitions, the measured cross sections are lower than their standard values due to significant photoelectric absorption of the γ rays within the bulk-sample volume itself. Using standard theoretical techniques, the amount of γ-ray self absorption and neutron self shielding can then be calculated by iteratively varying the sample thickness until the observed cross sections converge with the known standards. The overall attenuation, thus, provides a measure of the effective sample thickness illuminated by the neutron beam. This procedure is illustrated through radiative neutron capture using powdered oxide samples comprising enriched 186W and 182W from which their tungsten-equivalent effective thicknesses are deduced to be 0.077(3)mm and 0.042(8)mm, respectively.

Studies of54,56Fe Neutron Scattering Cross Sections

Elastic and inelastic neutron scattering differential cross sections and γ-ray production cross sections have been measured on 54,56 Fe at several incident energies in the fast neutron region between 1.5 and 4.7 MeV. All measurements were completed at the University of Kentucky Accelerator Laboratory (UKAL) using a 7-MV Model CN Van de Graaff accelerator, along with the neutron production and neutron and γ-ray detection systems located there. The facilities at UKAL allow the investigation of both elastic and inelastic scattering with nearly mono-energetic incident neutrons. Time-of-flight techniques were used to detect the scattered neutrons for the differential cross section measurements. The measured cross sections are important for fission reactor applications and also for testing global model calculations such as those found at ENDF, since describing both the elastic and inelastic scattering is important for determining the direct and compound components of the scattering mechanism. The γ-ray production cross sections are used to determine cross sections to unresolved levels in the neutron scattering experiments. Results from our measurements and comparisons to model calculations are presented.

γ-ray production cross sections of inelastic neutron scattering on natural molybdenum

γ-ray production cross sections of inelastic neutron scattering have been measured for molybdenum using the (n,n’γ)-technique. The experiment was performed at the GELINA facility at the Institute for Reference Materials and Measurements (IRMM) with the Gamma Array for Inelastic Neutron Scattering (GAINS) setup. GAINS consisted of eight high purity germanium detectors at the time of this experiment. The sample was made of natural molybdenum, which includes seven isotopes (A = 92, 94, 95, 96, 97, 98, 100). The presence of so many isotopes in the sample leads to overlapping peaks in the spectra, which limits the amount of data that can be extracted from the analysis. Nevertheless, a total of 31 γ rays from the seven isotopes were analysed and γ-ray production cross sections were determined. Comparisons to other experimental results were made when such data was available. Also comparisons with model calculations were made with the Talys 1.6 code.

Undergraduate Measurements of Neutron Cross Sections

Undergraduate students at the University of Dallas have investigated basic properties of nuclei through γ-ray and neutron spectroscopy following neutron scattering. The former has been used primarily for nuclear structure investigations, while the latter has been used to measure neutron scattering cross sections important for fission reactor applications. A series of (n,n’) and (n,n’γ) measurements have been made on 54Fe and 56Fe to determine neutron cross sections for scattering to excited levels in these nuclei. The former provides the cross sections directly and the latter are used to deduce inelastic neutron scattering cross sections by measuring the γ-ray production cross sections to states not easily resolved in neutron spectroscopy. All measurements have been completed at the University of Kentucky Accelerator Laboratory using a 7-MV Model CN Van de Graaff accelerator, along with the neutron production and neutron and γ-ray detection systems located there. Students participate in accelerator operation, experimental setup, data acquisition, and data analyses. An overview of the research program and student contributions is presented.

Erratum to: A Parameterisation of γ-ray production cross-sections for pp interactions in a broad energy range

Erratum to: A Parameterisation of γ-ray production cross-sections for pp interactions in a broad energy range

Inelastic scattering of fast neutrons from excited states in 56Fe

Abstract Inelastic scattering of fast neutrons from 56Fe was studied at the photoneutron source nELBE. The neutron energies were determined on the basis of a time-of-flight measurement. Gamma-ray spectra were measured with a high-purity germanium detector. The inelastic scattering cross sections deduced from the present experiment in an energy range from 0.8 to 9.6 MeV agree within 15% with earlier data and with predictions of the statistical-reaction code Talys. In addition to the γ-ray production cross sections, level cross sections for the 2 + , 4 + and 6 + yrast states in 56Fe were deduced.

γ-ray production in neutral-current neutrino-oxygen interactions at energies above 200 MeV

We report the results of a calculation of the neutrino- and antineutrino-induced γ-ray production cross section for oxygen target. Our analysis is focused on the kinematical region of neutrino energy larger than ~200 MeV, in which single-nucleon knockout is known to be the dominant reaction mechanism. The numerical results have been obtained using a realistic model of the target spectral function, extensively tested against electron-nucleus scattering data. We find that at neutrino energy 600 MeV the fraction of neutral-current interactions leading to emission of γ-rays of energy larger than 6 MeV is ~41%, and that the contribution of the p3/2 state is overwhelming.

Partial γ-ray production cross sections for (n,xnγ) reactions in natural argon at 1-30 MeV

Partial γ-ray production cross sections for (n,xnγ) reactions in natural argon at 1-30 MeV

Calculation and analysis of n+ 90,91,92,94,96,natZr reactions in the En ⩽ 250 MeV energy range

All of reaction cross sections, angular distributions, energy spectra, γ-ray production cross sections, and the double differential cross section for neutron, proton, deuteron, triton, helium and alpha emission are calculated and analyzed for n+ 90,91,92,94,96,natZr at incident neutron energies from 0.1 to 250 MeV. The optical model, intranuclear cascade model, the unified Hauser–Feshbach theory and the exciton model which included the improved Iwamoto–Harada model are used. Theoretical calculated results are compared with existing experimental data and other evaluated data from ENDF/B-VI.8, ENDF/B-VII.0 and JENDL-3.3. The optical model potential parameters are obtained according to the experimental data of total, nonelastic cross sections and elastic scattering angular distributions.

Calculation and Analysis of n + 180,182,183,184,186,natW Reactions in the En ≤ 250 MeV Energy Range

According to the experimental data of total, nonelastic scattering cross sections and elastic scattering angular distributions of tungsten and its isotopes, a set of neutron optical model potential parameters is obtained. All of the reaction cross sections, angular distributions, energy spectra, γ-ray production cross sections, γ-ray production energy spectra, and the double-differential cross section for neutron, proton, deuteron, triton, helium, and alpha emission are calculated and analyzed for n + 180,182,183,184,186,natW at incident neutron energies from 0.1 to 250 MeV based on the nuclear model theory, which combines the optical model, the unified Hauser-Feshbach theory and exciton model, and the coupled channel theory. Theoretical calculations are compared with existing experimental data and other evaluated data from ENDF/B6.8 and JENDL-3.3.

Gamma-Ray Production Cross Sections in Multiple Channels for Neutron-Induced Reaction on 48Ti for En = 1 to 200 MeV

Prompt γ-ray production cross sections were measured on a 48Ti sample for incident neutron energies from 1 to 200 MeV. Partial γ-ray cross sections for transitions in 45-48Ti, 45-48Sc, and 43-45Ca were determined. The observation of about 130 transitions from 11 different isotopes in the present work provides a demanding test of reaction model calculations, and is the first study in this mass region to extract partial γ-ray cross sections for many different reaction channels over a wide range of incident neutron energies. The neutrons were produced by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center/Weapons Neutron Research facility. The prompt-reaction γ rays were detected with the large-scale Compton-suppressed GErmanium Array for Neutron Induced Excitations (GEANIE). Event neutron energies were determined by the time-of-flight technique. The γ-ray excitation functions were converted to partial γ-ray cross sections and then compared with model calculations using the enhanced GNASH reaction code. Compound nuclear, preequilibrium emission, and direct reaction mechanisms are included. Overall, the model calculations of the partial γ-ray cross sections are in good agreement with measured values.