Capture Reaction Cross Sections Research Articles

Measurement of the cross sections for 238U(n, γ)239U reaction in the energy range of 14.1–14.8 MeV using neutron activation method

The neutron capture reaction cross sections of 238U were measured at the neutron energies of 14.1, 14.5 and 14.8 MeV using the activation method and off-line γ-ray spectrometric technique. The induced gamma-ray activities were measured using a low background gamma ray spectrometer equipped with a high resolution HPGe detector. The excitation functions of the 238U(n,γ)239U reaction were also calculated theoretically using the TALYS-1.8 program and are in general agreement with experimental data. The experimentally determined cross sections were compared with the data in the literature, and the evaluated data of ENDF/B-VIII.0, JENDL-4.0, and CENDL-3.1, as well as calculated results from TALYS-1.8.

Effects of nonlocality of nuclear potentials on direct capture reactions

Calculations of the direct radiative capture reactions are made for the $^{48}$Ca$(n,\gamma)^{49}$Ca, $^7$Li$(n,\gamma)^8$Li and $^{12}$C$(p,\gamma)^{13}$N reactions with the Perey-Buck type nonlocal potentials using a potential model. Our results reproduce the experimental data reasonably well. From comparisons with results obtained by using local potentials, it is found that the cross sections of direct capture reactions may change by around 25\% due to the nonlcality of nuclear potentials.

Cross section measurements of proton capture reactions on Se isotopes relevant to the astrophysical p process

Cross sections of proton capture reactions on $^{74}\mathrm{Se}$, $^{78}\mathrm{Se}$, and $^{80}\mathrm{Se}$ have been measured at incident beam energies from 2 to 6 MeV, 1.7 to 3 MeV, and 1.5 to 3.5 MeV, respectively. In the case of $^{78,80}\mathrm{Se}$, cross sections were obtained from in-beam $\ensuremath{\gamma}$-angular distribution measurements, whereas for the $^{74}\mathrm{Se}$ isotope they were derived from off-beam activity measurements. The measured cross sections were compared with calculations performed with the nuclear reaction code talys (version 1.6). A good agreement between theory and experiment was found. Astrophysical $S$ factors and reaction rates deduced from the experimental and calculated cross sections were also compared and the impact of different nuclear ingredients in the calculations on the reaction rates was investigated. It was found that, for certain combinations of nuclear input models, the reaction rates obtained at temperatures relevant to $p$-process nucleosynthesis differ by a factor 2 at the most, differences that are well within the acceptable deviations of calculated $p$-nuclei abundances and observations.

Proton capture reaction cross section measurements on Er162 as a probe of statistical model calculations

It is crucial to measure reaction cross sections relevant to the astrophysical $\ensuremath{\gamma}$ process so that theoretical reaction rates can be tested and validated with experimental data. The total cross sections for the $^{162}\mathrm{Er}(p,\ensuremath{\gamma})^{163}\mathrm{Tm}$ and the $^{162}\mathrm{Er}(p,n)^{162}\mathrm{Tm}$ reactions have been measured by the activation method in center-of-mass energies from 3.973 to 8.944 MeV and from 5.962 to 8.944 MeV, respectively. The nucleus $^{162}\mathrm{Er}$ is the heaviest $p$ nuclide to be measured by the activation method using $\ensuremath{\gamma}$-ray spectroscopy, so far. It is important to note that the energy range for the $(p,\ensuremath{\gamma})$ reaction measurement covers a large fraction of the astrophysically relevant energy region between 2.71 and 5.34 MeV. The targets were prepared by evaporating $28.2%$ isotopically enriched $^{162}\mathrm{Er}_{2}{\mathrm{O}}_{3}$ powder onto carbon backing foils, and bombarded with proton beams provided by the FN Tandem Accelerator at the University of Notre Dame. The reaction yields have been determined by the observed activity of produced radioactive isotopes, which was detected offline by a high-purity germanium detector. The results are presented and compared with calculations from two statistical model codes: non-smoker and talys.

Algorithm for calculations of asymptotic nuclear coefficients using phase-shift data for charged-particle scattering

A new algorithm for the asymptotic nuclear coefficients calculation, which we call the $\Delta$-method, is proved and developed. This method was proposed in Ref. [O. L. Ram\'irez Su\'arez and J.-M. Sparenberg, arXiv: 1602.04082 [nucl-th] (2016)] but no proof was given. We apply it to the bound state situated near the channel threshold when the Sommerfeld parameter is quite large within the experimental energy region. As a result, the value of the conventional effective-range function $K_l(k^2)$ is actually defined by the Coulomb term. One of the resulting effects is the wrong description of energy behavior of the elastic scattering phase shift $\delta_l$ reproduced from the fitted total effective-range function $K_l(k^2)$. This leads to an improper value of the asymptotic normalization coefficient (ANC) value. No such problem arises if we fit only the nuclear term. The difference between the total effective-range function and the Coulomb part at real energies is the same as the nuclear term. Then we can proceed using just this $\Delta$-method to calculate the pole position values and the ANC. We apply it to the vertices $^4\rm{He}+ {^{12}\rm{C}}\longleftrightarrow {^{16}\rm{O}}$ and $^3\rm{He}+ {^4\rm{He}}\longleftrightarrow {^7\rm{Be}}$. The calculated ANCs can be used to find the radiative capture reaction cross sections of the transfers to the $^{16}\rm{O}$ bound final states as well as to the $^7\rm{Be}\longleftrightarrow {^7\rm{Be}}$. The calculated ANCs can be used to find the radiative capture reaction cross sections of the transfers to the $^{16}\rm{O}$ bound final states as well as to the $^7\rm{Be}$.

Determination of neutron capture cross sections of 232Th at 14.1 MeV and 14.8 MeV using the neutron activation method**Supported by Chinese TMSR Strategic Pioneer Science and Technology Project-The Th-U Fuel Physics Term (XDA02010100) and National Natural Science Foundation of China (11205076, 21327801)

The 232Th(n, γ)233Th neutron capture reaction cross sections were measured at average neutron energies of 14.1 MeV and 14.8 MeV using the activation method. The neutron flux was determined using the monitor reaction 27Al(n,α)24Na. The induced gamma-ray activities were measured using a low background gamma ray spectrometer equipped with a high resolution HPGe detector. The experimentally determined cross sections were compared with the data in the literature, and the evaluated data of ENDF/B-VII.1, JENDL-4.0u+, and CENDL-3.1. The excitation functions of the 232Th(n,γ)233Th reaction were also calculated theoretically using the TALYS1.6 computer code.

Transfer Excitation Processes Observed in N3+–He and O3+–He Collisions at Elab = 33 eV

We measured the relative state-selective differential cross sections (DCSs) for one-electron capture reactions using a crossed-beam apparatus. The scattering angle θlab studied in the laboratory frame ranged from −3.0 to 22° and the laboratory collision energy Elab was 33 eV. Only the transfer excitation processes, i.e., the electron capture reactions with the simultaneous excitation of the projectile, were observed. The DCSs were determined for the following reactions: N3+ (1s2 2s2 1S) + He (1s2 1S) → N2+ (1s2 2s2p2 2D) + He+ (1s 2S) + 10.3 eV, O3+ (1s2 2s2 2p 2P) + He (1s2 1S) → O2+ (1s2 2s 2p3 3P) + He+ (1s 2S) + 12.7 eV, and O3+ (1s2 2s2 2p 2P) + He (1s2 1S) → O2+ (1s2 2s 2p3 3D) + He+ (1s 2S) + 15.5 eV. In the N3+–He system, the DCSs for the reaction are zero at the center-of-mass angle θcm = 0 and show a peak at a certain angle and a shoulder at a larger angle. In the O3+–He system, the DCSs are again zero at θcm = 0. The capture process to the O2+ (1s2 2s 2p3 3P) state is mainly observed at smaller...

Radiative neutron capture cross sections onLu176at DANCE

The cross section of the neutron capture reaction $^{176}\mathrm{Lu}(n,\ensuremath{\gamma})$ has been measured for a wide incident neutron energy range with the Detector for Advanced Neutron Capture Experiments at the Los Alamos Neutron Science Center. The thermal neutron capture cross section was determined to be $(1912\ifmmode\pm\else\textpm\fi{}132)$ b for one of the Lu natural isotopes, $^{176}\mathrm{Lu}$. The resonance part was measured and compared to the Mughabghab's atlas using the $R$-matrix code, sammy. At higher neutron energies the measured cross sections are compared to ENDF/B-VII.1, JEFF-3.2, and BRC evaluated nuclear data. The Maxwellian averaged cross sections in a stellar plasma for thermal energies between 5 keV and 100 keV were extracted using these data.

Alpha capture reaction cross section measurements on Sb isotopes by activation method

Alpha induced reactions on natural and enriched antimony targets were investigated via the activation technique in the energy range from 9.74 MeV to 15.48 MeV, close to the upper end of the Gamow window at a temperature of 3 GK relevant to the γ-process. The experiments were carried out at the Institute for Nuclear Research, the Hungarian Academy of Sciences (MTA Atomki). 121Sb(α,γ)125I, 121Sb(α,n)124I and 123Sb(α,n)126I reactions were measured using a HPGe detector. In this work, the 121Sb(α,n)124 cross section results and the comparison with the theoretical predictions (obtained with standard settings of the statistical model codes NON-SMOKER and TALYS) were presented.

Continuum quasiparticle random-phase approximation for astrophysical direct neutron capture reactions on neutron-rich nuclei

We formulate a many-body theory to calculate the cross section of direct radiative neutron capture reaction by means of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximation (QRPA). A focus is put on very neutron-rich nuclei and low-energy neutron kinetic energy in the range of O(1 keV) - O(1 MeV), relevant for the rapid neutron-capture process of nucleosynthesis. We begin with the photo-absorption cross section and the E1 strength function, then, in order to apply the reciprocity theorem, we decompose the cross section into partial cross sections corresponding to different channels of one- and two-neutron emission decays of photo-excited states. Numerical example is shown for the photo-absorption of $^{142}$Sn and the neutron capture of $^{141}$Sn.

Calculation of cross-sections and astrophysical s-factors for the63Cu(α,n) and63Cu(α,γ) reactions

The cross sections and astrophysical S-factors of the 63 Cu(α,γ) and 63 Cu(α,n) reactions have been calculated. The radiative alpha capture reaction cross sections was calculated in the incident energy range of 3 to 10 MeV and the (α,n) reaction cross sections was calculated in the incident energy range of 7 and 16 MeV. In these theoretical calculations, the TALYS 1.6 and NON-SMOKER codes were used. Also for these reactions, it was calculated the astrophysical S-factors which describe the possibility of reaction in low energies. Obtained results were compared to the experimental data taken from EXFOR database.

Probing nuclear rates with Planck and BICEP2

Big Bang Nucleosynthesis (BBN) relates key cosmological parameters to the primordial abundance of light elements. In this paper, we point out that the recent observations of Cosmic Microwave Background anisotropies by the Planck satellite and by the BICEP2 experiment constrain these parameters with such a high level of accuracy that the primordial deuterium abundance can be inferred with remarkable precision. For a given cosmological model, one can obtain independent information on nuclear processes in the energy range relevant for BBN, which determine the eventual ^2H/H yield. In particular, assuming the standard cosmological model, we show that a combined analysis of Planck data and of recent deuterium abundance measurements in metal-poor damped Lyman-alpha systems provides independent information on the cross section of the radiative capture reaction d(p,\gamma)^3He converting deuterium into helium. Interestingly, the result is higher than the values suggested by a fit of present experimental data in the BBN energy range (10 - 300 keV), whereas it is in better agreement with ab initio theoretical calculations, based on models for the nuclear electromagnetic current derived from realistic interactions. Due to the correlation between the rate of the above nuclear process and the effective number of neutrinos Neff, the same analysis points out a Neff>3 as well. We show how this observation changes when assuming a non-minimal cosmological scenario. We conclude that further data on the d(p,\gamma)^3He cross section in the few hundred keV range, that can be collected by experiments like LUNA, may either confirm the low value of this rate, or rather give some hint in favour of next-to-minimal cosmological scenarios.

Alpha induced reaction cross section measurements on 162Er for the astrophysical γ process

The cross sections of the Er162(α,γ)Yb166 and Er162(α,n)Yb165 reactions have been measured for the first time. The radiative alpha capture reaction cross section was measured from Ec.m.=16.09 MeV down to Ec.m.=11.21 MeV, close to the astrophysically relevant region (which lies between 7.8 and 11.48 MeV at 3 GK stellar temperature). The Er162(α,n)Yb165 reaction was studied above the reaction threshold between Ec.m.=12.19 and 16.09 MeV. The fact that the Er162(α,γ)Yb166 cross sections were measured below the (α,n) threshold at first time in this mass region opens the opportunity to study directly the α-widths required for the determination of astrophysical reaction rates. The data clearly show that compound nucleus formation in this reaction proceeds differently than previously predicted.

A Nuclear Data Project on Neutron Capture Cross Sections of Long-Lived Fission Products and Minor Actinides

A nuclear data project entitled “Systematic Study on Neutron Capture Reaction Cross Sections for the Technological Development of Nuclear Transmutation of Long-Lived Nuclear Wastes” is being performed. The objective of the project is to improve nuclear data libraries, by making the precise measurements of neutron capture cross sections of Long-Lived Nuclear Wastes (LLNWs), analyzing the measured results theoretically, and supplying reliable calculated capture cross sections for the LLNWs. This contribution presents the outline of the project, and individual results are presented by other contributions.

Radiative capture reactions with heavy beams: extending the capabilities of DRAGON

Understanding the nucleosynthesis of stable proton-rich nuclei requires knowledge of the cross sections for both proton and alpha capture reactions. As some of the nucleosynthesis paths responsible for the production of these nuclei involve reactions on unstable isotopes, it is of particular importance to develop techniques to investigate these reactions. This requires radioactive beams and measurements in inverse kinematics, thus making recoil separators an ideal tool for direct measurements of proton and alpha capture reactions. Here, the application of the DRAGON recoil separator for measurements of capture reactions for heavy beams is presented. The performance of the separator was tested using the 58Ni(p,γ)59Cu reaction.

Photonuclear and radiative-capture reaction rates for nuclear astrophysics and transmutation:92–100Mo,88Sr,90Zr, and139La

Experimental photoabsorption cross sections for the nuclei ${}^{92,94,96,98,100}$Mo, ${}^{88}$Sr, ${}^{90}$Zr, and ${}^{139}$La are used as an input for calculations of $(\ensuremath{\gamma},n)$, $(\ensuremath{\gamma},p),$ and $(\ensuremath{\gamma},\ensuremath{\alpha})$, as well as $(n,\ensuremath{\gamma})$, $(p,\ensuremath{\gamma}),$ and $(\ensuremath{\alpha},\ensuremath{\gamma})$ cross sections and reaction rates at energies and temperatures relevant for nucleosynthesis network models and transmutation projects. The calculations are performed with the statistical-model code talys. The results are compared with those obtained by using different analytic standard parametrizations of $\ensuremath{\gamma}$-ray strength functions implemented in talys and with an energy-damped double-Lorentzian model. The radiative capture reaction cross sections are enhanced by the pygmy resonances in ${}^{88}$Sr, ${}^{90}$Zr, and ${}^{139}$La.

AstrophysicalSfactor for the radiative captureN12(p,γ)O13determined from theN14(N12,O13)C13proton transfer reaction

The cross section of the radiative proton capture reaction on the drip line nucleus $^{12}\mathrm{N}$ was investigated using the asymptotic normalization coefficient (ANC) method. We have used the $^{14}\mathrm{N}(^{12}\mathrm{N},^{13}\mathrm{O})^{13}\mathrm{C}$ proton transfer reaction at 12 MeV/nucleon to extract the ANC for $^{13}\mathrm{O}\ensuremath{\rightarrow}^{12}\mathrm{N}+p$ and calculate from it the direct component of the astrophysical $S$ factor of the $^{12}\mathrm{N}(p,\ensuremath{\gamma})^{13}\mathrm{O}$ reaction. The optical potentials used and the distorted-wave Born approximation analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time as the transfer measurement. From the transfer, we determined the square of the ANC, ${C}_{{p}_{1/2}}^{2}(^{13}\mathrm{O}{}_{\mathrm{g}.\mathrm{s}.})=2.53\ifmmode\pm\else\textpm\fi{}0.30 {\mathrm{fm}}^{\ensuremath{-}1}$, and hence a value of $0.33(4) \mathrm{keV}$ b was obtained for the direct astrophysical $S$ factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of ${S}_{\mathrm{total}}(0)=0.42(6) \mathrm{keV}$ b. The $^{12}\mathrm{N}(p,\ensuremath{\gamma})^{13}\mathrm{O}$ reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot $\mathit{pp}$-chain nuclear burning processes, possibly occurring in such objects.

Cross-section measurements of capture reactions relevant to the p process using a4πγ-summing method

A new method employing a 12 inch \ifmmode\times\else\texttimes\fi{} 12 inch \ensuremath{\gamma}-summing single NaI crystal was developed for cross-section measurements of astrophysically relevant capture reactions on medium-mass nuclei. The response function of such a $4\ensuremath{\pi}$ detector enables the summing of all capture events. As a result, a single peak, the so-called sum peak, arises in the spectra. Its intensity can be used to obtain cross sections of capture reactions with unknown multiplicities. The method enables to first determine these multiplicities, which are then used to derive the corresponding efficiency of the sum peak by means of Monte Carlo simulations. Cross sections are finally obtained from the sum-peak intensity with an average uncertainty of $\ensuremath{\approx}15%$. The method was first applied to the $^{62}\mathrm{Ni}$($\ensuremath{\alpha},\ensuremath{\gamma}$)$^{66}\mathrm{Zn}$ reaction. The results obtained are in excellent agreement with those reported in literature. The new method proposed here was then employed to determine cross sections of 25 capture reactions in the Ni--Sb region. The cross sections measured for the $^{103}\mathrm{Rh}$($p,\ensuremath{\gamma}$)$^{104}\mathrm{Pd}$ reaction are also presented. A very good agreement between the cross sections measured in the present work and the corresponding predictions of the Hauser-Feshbach theory was found.

Nuclear reactions in hot stellar matter and nuclear surface deformations

Cross sections for capture reactions of charged particles in hot stellar matter turn out be increased by the quadrupole surface oscillations when the corresponding phonon energies are of the order of the star temperature. This increase is studied in a model that combines barrier distribution induced by surface oscillations and tunneling. The capture of charged particles by nuclei with well-deformed ground states is enhanced in stellar matter. It is found that the influence of quadrupole surface deformation on the nuclear reactions in stars grows when mass and proton numbers in colliding nuclei increase.

Cross Section of Thermal-Neutron Capture Reaction by 99Tc

Cross Section of Thermal-Neutron Capture Reaction by 99Tc