14N(p,gamma)15O is one of the key reactions of nuclear astrophysics playing a role in various stellar processes and influencing energy generation of stars, stellar evolution and nucleosynthesis. For a reliable reaction rate calculation the low energy cross section of 14N(p,gamma)15O must be known with high accuracy. Owing to the unmeasurable low cross sections, theoretical calculations are unavoidable. High precision experimental cross section data are needed in a wide energy range in order to provide the necessary basis for low energy extrapolations. In the present work the total 14N(p,gamma)15O cross section was measured with a method complementary to the available data sets. The cross section was measured with activation, based on the detection of the annihilation radiation following the beta+ decay of the reaction product 15O. This method, which provides directly the astrophysically important total cross section, was never used for the 14N(p,gamma)15O cross section measurement in the studied energy range. The non-resonant cross section was measured between 550 keV and 1400 keV center-of-mass energies with total uncertainty of about 10%. The results were compared with literature data using an R-matrix analysis. It is found that the cross sections measured in this work are in acceptable agreement with the two recent measurements only if the weak transitions - not measured in those works - are included. The present data set, being largely independent from the other available data, can be used to constrain the extrapolated cross sections to astrophysical energies and helps to make the astrophysical model calculations more reliable.
The 14N(p,gamma)15O reaction plays a vital role in various astrophysical scenarios. Its reaction rate must be accurately known in the present era of high precision astrophysics. The cross section of the reaction is often measured relative to a low energy resonance, the strength of which must therefore be determined precisely. The activation method, based on the measurement of 15O decay, has not been used in modern measurements of the 14N(p,gamma)15O reaction. The aim of the present work is to provide strength data for two resonances in the 14N(p,gamma)15O reaction using the activation method. …
In order to extend the experimental database relevant for the astrophysical gamma-process towards the unexplored heavier mass region, the cross sections of the 151Eu(alpha,gamma)155Tb and 151Eu(alpha,n)154Tb reactions have been measured at low energies between 12 and 17 MeV using the activation technique. The results are compared with the predictions of statistical model calculations and it is found that the calculations overestimate the cross sections by about a factor of two. A sensitivity analysis shows that this discrepancy is caused by the inadequate description of the alpha+nucleus chann…
The primary aim of experimental nuclear astrophysics is to determine the rates of nuclear reactions taking place in stars in various astrophysical conditions. These reaction rates are important ingredient for understanding the elemental abundance distribution in our solar system and the galaxy. The reaction rates are determined from the cross sections which need to be measured at energies as close to the astrophysically relevant ones as possible. In many cases the final nucleus of an astrophysically important reaction is radioactive which allows the cross section to be determined based on the …
The reaction 141Pr(alpha,n)144Pm was investigated between E_alpha=11 MeV and 15 MeV with the activation method using the gamma-gamma coincidence method with a segmented clover-type high-purity Germanium (HPGe) detector. Measurements with four other HPGe detectors were additionally made. The comparison proves that the gamma-gamma coincidence method is an excellent tool to investigate cross sections down to the microbarn range. The (alpha,n) reaction at low energy is especially suited to test alpha+nucleus optical-model potentials for application in the astrophysical p-process. The experimentall…
The synthesis of heavy, proton rich isotopes in the astrophysical gamma-process proceeds through photodisintegration reactions. For the improved understanding of the process, the rates of the involved nuclear reactions must be known. The reaction 128Ba(g,a)124Xe was found to affect the abundance of the p nucleus 124Xe. Since the stellar rate for this reaction cannot be determined by a measurement directly, the aim of the present work was to measure the cross section of the inverse 124Xe(a,g)128Ba reaction and to compare the results with statistical model predictions. Of great importance is the…
In nuclear astrophysics, the experimental scenario is still unclear for BBN relevant energies from 30-300 keV. Here, we report our measurements of cross section and astrophysical S(E) factor for pd capture reaction using proton beam energies 66 keV, 116 keV and 166 keV. Realistic GEANT4 simulations were carried out in order to estimate the energy dependent efficiency of the detector. The measured cross section and astrophysical S(E) factor for three new incident proton energies are found to be in good agreement, within the errors, with the values reported in the literature.
For the synthesis of the heavy, proton rich isotopes in the astrophysical gamma-process the precise knowledge of alpha-induced cross sections is of high importance. We have initiated a comprehensive study of the 64Zn+alpha system involving the cross section measurement of different reaction channels as well as the elastic scattering at low, astrophysically relevant energies. In this paper the experimental technique and some preliminary results of the 64Zn(alpha,p)67Ga cross section measurement are presented.
(Shorten version of the PRC abstract) Alpha-induced reactions on 127I have been studied using the activation technique in order to provide cross section data for the modeling of the astrophysical gamma process. The relative intensity of the 536.1 keV gamma transition was measured precisely, its uncertainty was reduced from 13% to 4%. By measuring the yield of the characteristic X-rays, the cross sections of the 127I(alpha,gamma)131Cs reaction have been determined for the first time close to the astrophysically relevant energy region, at energies 9.50 < Ec.m. < 15.15$ MeV. The 127I(alpha,n)130C…
The synthesis of heavy, proton rich isotopes is a poorly understood astrophysical process. Thermonuclear (type Ia) supernova explosions are among the suggested sites and the abundance of some isotopes present in the early solar system may be used to test the models. 92Nb is such an isotope and one of the reactions playing a role in its synthesis is 91Zr(p,gamma)92Nb. As no experimental cross sections were available for this reaction so far, nucleosynthesis models had to solely rely on theoretical calculations. In the present work the cross section of 91Zr(p,gamma)92mNb has been measured at ast…
In a recent work, the cross section measurement of the 64Zn(p,alpha)61Cu reaction was used to prove that the standard alpha-nucleus optical potentials used in astrophysical network calculation fail to reproduce the experimental data at energies relevant for heavy element nucleosynthesis. In the present paper the analysis of the obtained experimental data is continued by comparing the results with the predictions using different parameters. It is shown that the recently suggested modification of the standard optical potential leads to a better description of the data.
Proton-activation reactions on natural and enriched palladium samples were investigated via the activation technique in the energy range of E_p=2.75 MeV to 9 MeV, close to the upper end of the respective Gamow window of the gamma process. We have determined cross sections for 102Pd(p,gamma)103Ag, 104Pd(p,gamma)105Ag, and 105Pd(p,n)105Ag, as well as partial cross sections of 104Pd(p,n)104Ag^g, 105Pd(p,gamma)106Ag^m, 106Pd(p,n)106Ag^m, and 110Pd(p,n)110Ag^m with uncertainties between 3% and 15% for constraining theoretical Hauser-Feshbach rates and for direct use in gamma-process calculations.
Reaction cross sections of 169Tm(alpha,gamma)173Lu and 169Tm(alpha,n)172Lu have been measured in the energy range 12.6<=E_alpha<=17.5 MeV and 11.5<=E_alpha<=17.5 MeV, respectively, using the recently introduced method of combining activation with X-ray counting. Improved shielding allowed to measure the (alpha,gamma) to lower energy than previously possible. The combination of (alpha,gamma) and (alpha,n) data made it possible to study the energy dependence of the alpha width. While absolute value and energy dependence are perfectly reproduced by theory at energies above 14 MeV, the observed ch…
Primary gamma-ray spectra for a wide excitation-energy range have been extracted for 44Ti from particle-gamma coincidence data of the 46Ti(p,t gamma)44Ti reaction. These spectra reveal information on the gamma-decay pattern of the nucleus, and may be used to extract the level density and radiative strength function applying the Oslo method. Models of the level density and radiative strength function are used as input for cross-section calculations of the 40Ca(alpha,gamma)44Ti reaction. Acceptable models should reproduce data on the 40Ca(alpha,gamma)44Ti reaction cross section as well as the me…
Two effects relevant for the study of astrophysical reaction rates: gamma transitions in capture reactions and Coulomb suppression of the stellar enhancement
Samples of two characteristic semiconductor sensor materials, silicon and germanium, have been irradiated with neutrons produced at the RP-10 Nuclear Research Reactor at 4.5 MW. Their radionuclides photon spectra have been measured with high resolution gamma spectroscopy, quantifying four radioisotopes ($^{28}$Al, $^{29}$Al for Si and $^{75}$Ge and $^{77}$Ge for Ge). We have compared the radionuclides production and their emission spectrum data with Monte Carlo simulation results from FLUKA. Thus we have tested FLUKA's low energy neutron library (ENDF/B-VIIR) and decay photon scoring with resp…
An air cargo inspection system combining two nuclear reaction based techniques, namely Fast-Neutron Resonance Radiography and Dual-Discrete-Energy Gamma Radiography is currently being developed. This system is expected to allow detection of standard and improvised explosives as well as special nuclear materials. An important aspect for the applicability of nuclear techniques in an airport inspection facility is the inventory and lifetimes of radioactive isotopes produced by the neutron and gamma radiation inside the cargo, as well as the dose delivered by these isotopes to people in contact wi…
The cross sections of the 162Er(a,g,)166Yb and 162Er(a,n)165Yb reactions have been measured for the first time. The radiative alpha capture reaction cross section was measured from Ec.m. = 16.09 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 162Er(a,n)165Yb reaction was studied above the reaction threshold between Ec.m. = 12.19 and 16.09 MeV. The fact that the 162Er(a,g)166Yb cross sections were measured below the (a,n) threshold at first time in this mass region opens the opportunity to study dire…
For the better understanding of the astrophysical gamma-process the experimental determination of low energy proton- and alpha-capture cross sections on heavy isotopes is required. The existing data for the 92Mo(p,gamma)93Tc reaction are contradictory and strong fluctuation of the cross section is observed which cannot be explained by the statistical model. In this paper a new determination of the 92Mo(p,gamma)93Tc and 98Mo(p,gamma)99mTc cross sections based on thick target yield measurements are presented and the results are compared with existing data and model calculations. Reaction rates o…
The 17O(p,g)18F reaction plays an important role in hydrogen burning processes in different stages of stellar evolution. The rate of this reaction must therefore be known with high accuracy in order to provide the necessary input for astrophysical models. The cross section of 17O(p,g)18F is characterized by a complicated resonance structure at low energies. Experimental data, however, is scarce in a wide energy range which increases the uncertainty of the low energy extrapolations. The purpose of the present work is therefore to provide consistent and precise cross section values in a wide ene…
Effective energy windows (Gamow windows) of astrophysical reaction rates for (p,gamma), (p,n), (p,alpha), (alpha,gamma), (alpha,n), (alpha,p), (n,gamma), (n,p), and (n,alpha) on targets with 10<=Z<=83 from proton- to neutron-dripline are calculated using theoretical cross sections. It is shown that widely used approximation formulas for the relevant energy ranges are not valid for a large number of reactions relevant to hydrostatic and explosive nucleosynthesis. The influence of the energy dependence of the averaged widths on the location of the Gamow windows is discussed and the results prese…
Photoactivation measurements on 144Sm have been performed with bremsstrahlung endpoint energies from 10.0 to 15.5 MeV at the bremsstrahlung facility of the superconducting electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf. The measured activation yield for the 144Sm(gamma,n) reaction is compared with the calculated yield using cross sections from previous photoneutron experiments. The activation yields measured for all disintegration channels 144Sm(gamma,n), (gamma,p) and (gamma,alpha) are compared to the yield calculated by using Hauser-Feshbach statistical models. A new param…
Captures of alpha particles on the proton-richest Barium isotope, 130Ba, have been studied in order to provide cross section data for the modeling of the astrophysical gamma process. The cross sections of the 130Ba(alpha,gamma)134Ce and 130Ba(alpha,n)133Ce reactions have been measured with the activation technique in the center-of mass energy range between 11.6 and 16 MeV, close above the astrophysically relevant energies. As a side result, the cross section of the 132Ba(alpha,n)135Ce reaction has also been measured. The results are compared with the prediction of statistical model calculation…
The astrophysically important 3He(a,g)7Be reaction was studied at high energies where the available experimental data are in contradiction. A thin window 3He gas cell was used and the cross section was measured with the activation method. The obtained cross sections at energies between Ec.m. = 1.5 and 2.5 MeV are compared with the available data and theoretical calculations. The present results support the validity of the high energy cross section energy dependence observed by recent experiments.
In the present work we report on a new measurement of resonance strengths in the reaction 25Mg(p,gamma)26Al at E_cm= 92 and 189 keV. This study was performed at the LUNA facility in the Gran Sasso underground laboratory using a 4pi BGO summing crystal. For the first time the 92 keV resonance was directly observed and a resonance strength omega-gamma=(2.9+/-0.6)x10E-10 eV was determined. Additionally, the gamma-ray branchings and strength of the 189 keV resonance were studied with a high resolution HPGe detector yielding an omega-gamma value in agreement with the BGO measurement, but 20% larger…
Spectra of the 9Be(e,e') reaction have been measured at the S-DALINAC at an electron energy E_0 = 73 MeV and scattering angles of 93° and 141° with high energy resolution up to excitation energies E_x = 8 MeV. The astrophysically relevant resonance parameters of the first excited 1/2+ state of 9Be have been extracted in a one-level approximation of R-matrix theory resulting in a resonance energy E_R = 1.748(6) MeV and width Gamma_R = 274(8) keV in good agreement with the latest 9Be(gamma,n) experiment but with considerably improved uncertainties. However, the reduced B(E1) transition strength …
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 literatures data, evaluated data of ENDF/B-VII, JENDL-4.0, and CENDL-3.1. The Excitation functions of 232Th(n,γ) reaction were also calculated theoretically using…
Gamma-ray production cross sections in proton interactions with natMg, natSi and 56Fe targets: measurement over the energy range of $E_p = 66$-125 MeV, data analysis, results and discussion. Astrophysical implications
University of Sciences and Technology Houari Boumediene (USTHB)（哈立迪·布迈丁科技大学）；Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM)（核科学与物质科学中心）；iThemba LABS（iThemba实验室）；CRNA（阿尔及利亚核研究与应用研究中心）；University M’Hamed Bougara（穆罕默德·布格拉大学）；Department of Physics, University of the Western Cape（西开普大学物理系）；Institut de Physique Nucléaire (IPN)（核物理研究所）；Department of Physics, Stellenbosch University（斯坦伦布什大学物理系）；Department of Physics, University of Zululand（祖鲁兰大学物理系）；Department of Physics and Engineering University of Zululand（祖鲁兰大学物理与工程系）；Department of Physics, University of Cape Town（开普敦大学物理系）
Experimental excitation functions for long-lived products in proton induced reactions were measured with the activation method in the 37-65 MeV energy range on natural holmium. Stacked foil irradiation technique and high resolution gamma spectrometry were used in order to measure cross-section data for the production of $^{161}$Er, $^{160}$Er and $^{159,157}$Dy. For comparison of the production routes of medically related $^{161}$Er and $^{160}$Er radioisotopes new experimental cross section data were deduced for the $^{162}$Er(p,x)$^{161,160}$Er and $^{162}$Er(d,x)$^{161,160}$Er reactions by …
A dedicated setup for the in-beam measurement of absolute cross sections of astrophysically relevant charged-particle induced reactions is presented. These, usually very low, cross sections at energies of astrophysical interest are important to improve the modeling of the nucleosynthesis processes of heavy nuclei. Particular emphasis is put on the production of the $p$ nuclei during the astrophysical $γ$ process. The recently developed setup utilizes the high-efficiency $γ$-ray spectrometer HORUS, which is located at the 10 MV FN tandem ion accelerator of the Institute for Nuclear Physics in C…
Activation cross sections of the natEr(d,x)163,165,166,167,168,170Tm and natEr(d,x)171,161Er nuclear reactions have been measured in the 32-50 MeV energy range, above 40 MeV for the first time. The activation method with stacked foil irradiation technique and gamma-ray spectroscopy were used. The experimental cross sections were compared with the theoretical predictions in the TENDL-2015 library.
The cross sections of 151Eu(alpha,gamma)155Tb and 151Eu(alpha,n)154Tb reactions have been measured with the activation method. Some aspects of the measurement are presented here to illustrate the requirements of experimental techniques needed to obtain nuclear data for the astrophysical p-process nucleosynthesis. Preliminary cross section results are also presented and compared with the predictions of statistical model calculations.
We have measured the gamma-ray line production cross sections in proton-induced nuclear reactions on various target nuclei abundant in astrophysical sites over the incident energy range of Ep = 30 - 200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 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 gamma-ray spectra. In the current paper, we focus on de-excitation lines produced in proton irradiations of natC and Mylar target…
