Radiative Capture Cross Sections Research Articles

Measurement of the 238U Radiative Capture Cross Section with C6D6 at the CERN n_TOF Facility

We present the preliminary results of the 238U(n,γ) reaction cross section measurement, performed on April 2012 at the CERN n_TOF facility using C6D6 scintillation detectors over an energy range from thermal to 1 MeV. The goal of this measurement, which is part of a larger proposal, is to reach an uncertainty of 2% in the cross section. The experimental set-up and the methods used to obtain this result are described.

Determination of the 151Eu(n,γ)[formula omitted]Eu and 153Eu(n,γ)154Eu Reaction Cross Sections at Thermal Neutron Energy

We have measured partial γ-ray cross sections following neutron capture in enriched 151Eu and 153Eu targets at the cold-neutron-beam facility of the Budapest Research Reactor. The cross sections were standardized using a stoichiometric natEuCl3 target with the well-known 1951-keV γ-ray cross section from the 35Cl(n,γ)36Cl reaction at the cold-neutron-beam facility of the Garching Research Reactor. The γ-ray cross sections were corrected for effective g-factors. These data were combined with the structural information of 152Eu and 154Eu given in the Evaluated Nuclear Structure Data File to produce capture γ-ray level schemes. The total radiative capture cross sections of the 151Eu(n,γ)152m1,gEu and 153Eu(n,γ)154Eu reactions were determined by summing the experimental transition intensities from known levels with simulated intensities of transitions from higher excitations to the ground- or metastable-state. The individual 151Eu(n,γ)152m1Eu and 151Eu(n,γ)152gEu reaction cross sections disagree with values in the literature. However, the total cross section of the 151Eu(n,γ)152Eu reaction does agree with those values. Also, our deduced cross section for the 153Eu(n,γ)154Eu reaction closely follows the data in the literature. These results are supported by an earlier standardization experiment done at the Budapest Research Reactor using a target of Eu2O3 solution in H2SO4.

Effective field theory calculation of two-deuteron radiative capture reaction at astrophysical energies

Two-deuteron radiative capture reaction is one of the deuterium-burning processes that the cross section is not well known at very low-energies. We develop the formalism based on pionless Effective Field Theory (EFT) for deuteron–deuteron (dd) scattering to derive the cross section of two-deuteron radiative capture. Within this formalism the two- and three-body forces, should also be included in the capture cross section calculations. The aim of the present work is to calculate the observables of the low-energy dd photonuclear reactions. The cross section and the astrophysical S-factor for the 2H(d,γ)4He reaction have been calculated. The 4He is studied as four-body bound states in the pionless EFT. The theoretical uncertainties for observables are estimated based on the variation of the cutoffs. The astrophysical S-factor is accurately determined to be 6.9×10−6 keV b (6.1×10−6 keV b) for two-body (two- and three-body) at zero energy. A satisfactory agreement between theory and experiment for dd radiative capture observables up to order of calculation has been found by insertion of three-body force.

Interaction of Fast Nucleons with Actinide Nuclei Studied with GEANT4

We model interactions of protons and neutrons with energies from 1 to 1000 MeV with 241Am and 243Am nuclei. The calculations are performed with the Monte Carlo model for Accelerator Driven Systems (MCADS) which we developed based on the GEANT4 toolkit of version 9.4. This toolkit is widely used to simulate the propagation of particles in various materials which contain nuclei up to uranium. After several extensions we apply this toolkit also to proton- and neutron-induced reactions on Am. The fission and radiative neutron capture cross sections, neutron multiplicities and distributions of fission fragments were calculated for 241Am and 243Am and compared with experimental data. As demonstrated, the fission of americium by energetic protons with energies above 20 MeV can be well described by the Intra-Nuclear Cascade Liège (INCL) model combined with the fission-evaporation model ABLA. The calculated average numbers of fission neutrons and mass distributions of fission products agree well with the corresponding data. However, the proton-induced fission below 20 MeV is described less accurately. This is attributed to the limitations of the Intra-Nuclear Cascade model at low projectile energies.

Effective field theory for proton halo nuclei

We use halo effective field theory to analyze the universal features of proton halo nuclei bound due to a large S-wave scattering length. With a Lagrangian built from effective core and valence-proton fields, we derive a leading-order expression for the charge form factor. Within the same framework we also calculate the radiative proton capture cross section. Our general results at leading order are applied to study the excited 1/2+ state of Fluorine-17, and we give results for the charge radius and the astrophysical S-factor.

Study of the $^{15}$O$(2p,\gamma )^{17}$Ne Cross Section by Coulomb Dissociation of $^{17}$Ne for the $rp$ Process of Nucleosynthesis

The O-15(2p, gamma)Ne-17 cross section has been studied by the inverse reaction, the Coulomb dissociation of Ne-17. The experiment has been performed at the GSI. The Ne-17 excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb dissociation cross sections (sigma(Coul)) have been extracted, which provide a photoabsorption (sigma(photo)) and a radiative capture cross section (sigma(cap)). Additionally, important information about the Ne-17 nuclear structure will be obtained. The analysis is in progress.

238U(n,γ) reaction cross section measurement with C6D6detectors at the n_TOF CERN facility.

The radiative capture cross section of 238U is very important for the developing of new reactor technologies and the safety of existing ones. Here the preliminary results of the 238U(n,γ) cross section measurement performed at n_TOF with C6D6 scintillation detectors are presented, paying particular attention to data reduction and background subtraction.

Radiative Capture of Neutrons on 12C at Astrophysical Energies

Within the framework of the potential cluster model with classification of orbital state according to the Young schemes, the possibility of a description of experimental data for the total cross sections of radiative n 12C capture at energies from 25 meV (25⋅10-3 eV) to 550 keV to the ground state and three excited levels of the 13С nucleus is considered. It is shown that it is entirely possible to explain the magnitude of the cross sections in the considered energy range on the basis of only E1 transitions from various states of n 12C scattering to these bound states of the 13C nucleus in the n 12C channel.

Measurements of ultracold neutron upscattering and absorption in polyethylene and vanadium

The study of neutron cross sections for elements used as efficient “absorbers” of ultracold neutrons (UCN) is crucial for many precision experiments in nuclear and particle physics, cosmology and gravity. In this context, “absorption” includes both the capture and upscattering of neutrons to the energies above the UCN energy region. The available data, especially for hydrogen, do not agree between themselves or with the theory. In this report we describe measurements performed at the Los Alamos National Laboratory UCN facility of the UCN upscattering cross sections for vanadium and for hydrogen in CH2 using simultaneous measurements of the radiative capture cross sections for these elements. We measured σup=1972±130 b for hydrogen in CH2, which is below theoretical expectations, and σup=25±9 b for vanadium, in agreement with the expectation for the neutron heating by thermal excitations in solids.Received 5 June 2013DOI:https://doi.org/10.1103/PhysRevC.88.037601This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society

Application of Radiogenic Lead with Dominant Content of 208Pb for Long Prompt Neutron Lifetime in Fast Reactor

As a rule, materials of small atomic weight (light and heavy water, graphite, and so on) are used as neutron moderators and reflectors. A new very heavy atomic weight moderator is proposed - radiogenic lead consisting mainly of isotope 208Pb. It is characterized by extremely small neutron radiative capture cross section ([approximately]0.23 mb for thermal neutrons, i.e., less than that for graphite and deuterium) and highest albedo of thermal neutrons.The use of radiogenic lead to make it possible to slow down the chain fission reaction on prompt neutrons in a fast reactor is evaluated. This can improve the safety of a fast reactor.It is noteworthy that radiogenic lead with high 208Pb content may be recovered from thorium (as well as thorium-uranium) ores without isotope separation. This has been confirmed experimentally by the investigations performed at the University of São Paulo in Brazil.

Photoneutron cross sections for Mo isotopes: A step toward a unified understanding of(γ,n)and(n,γ)reactions

Photoneutron cross sections were measured for ${}^{94}$Mo, ${}^{95}$Mo, ${}^{96}$Mo, ${}^{97}$Mo, ${}^{98}$Mo, and ${}^{100}$Mo near the neutron threshold with quasi-monochromatic laser-Compton scattering $\ensuremath{\gamma}$ rays. The photoneutron data were analyzed with the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasiparticle random phase approximation (QRPA) model and the axially symmetric-deformed Gogny HFB plus QRPA model of $E1$ $\ensuremath{\gamma}$-ray strength. Combining the $\ensuremath{\gamma}$-ray strength function constrained by the present photoneutron data with either the nuclear resonance fluorescence data or the updated Oslo data to supplement the data below the neutron threshold, a thorough analysis of the reverse $(n,\ensuremath{\gamma})$ cross sections is made whenever measurements are available. The Oslo data and the corresponding uncertainties are updated based on the latest results of the $s$-wave neutron spacing and the average radiative width determined in particular for ${}^{96}$Mo. Finally, radiative neutron capture cross sections for two radioactive nuclei, ${}^{93}$Mo and ${}^{99}$Mo, are deduced with the $\ensuremath{\gamma}$-ray strength function method.

Radiative n 14N capture at astrophysical energies

The total cross sections of the 16O(n,gamma)17O radiative capture process is described in the framework of the modified potential cluster model with the classification of orbital states according to Young tableaux. The possibility to describe the experimental data for the total cross sections of the neutron radiative capture on 16O at the energies from 0.025 eV to 1.5 MeV is shown on the basis of E1 and M1 processes. The transitions to the bound states of 17O in the n16O channel from 2S1/2, 2P3/2 and 2D3/2 waves of the n16O scattering have been considered. These transitions have been considered in the resonance energy region at 433 and 1000 keV.

Calculation of the cross section of radiative double-electron capture by a bare nucleus with emission of one photon

We present a calculation of the cross section for the process of double-electron capture by a bare nucleus with emission of a single photon. The calculation is performed within the framework of quantum electrodynamics. The cross section is presented as a function of the incident-electron energy for ions with the nuclear charge within the interval $8\ensuremath{\le}Z\ensuremath{\le}92$. The available experiments on the double-electron capture by a bare nucleus are discussed.

Databases and tools for nuclear astrophysics applications

An update of a previous description of the BRUSLIB+NACRE package of nuclear data for astrophysics and of the web-based nuclear network generator NETGEN is presented. The new version of BRUSLIB contains the latest predictions of a wide variety of nuclear data based on the most recent version of the Brussels-Montreal Skyrme-HFB model. The nuclear masses, radii, spin/parities, deformations, single-particle schemes, matter densities, nuclear level densities, E1 strength functions, fission properties, and partition functions are provided for all nuclei lying between the proton and neutron drip lines over the 8<=Z<=110 range, whose evaluation is based on a unique microscopic model that ensures a good compromise between accuracy, reliability, and feasibility. In addition, these various ingredients are used to calculate about 100000 Hauser-Feshbach n-, p-, a-, and gamma-induced reaction rates based on the reaction code TALYS. NACRE is superseded by the NACRE II compilation for 15 charged-particle transfer reactions and 19 charged-particle radiative captures on stable targets with mass numbers A < 16. NACRE II features the inclusion of experimental data made available after the publication of NACRE in 1999 and up to 2011. In addition, the extrapolation of the available data to the very low energies of astrophysical relevance is improved through the systematic use of potential models. Uncertainties in the rates are also evaluated on this basis. The latest release of the web-based tool NETGEN is presented. It contains in a fully documented form the new BRUSLIB and NACRE II data, as well as new experiment-based radiative neutron capture cross sections. The full new versions of BRUSLIB, NACRE II, and NETGEN are available electronically at http://www.astro.ulb.ac.be/NuclearData. The nuclear material is presented in an extended tabular form complemented with a variety of graphical interfaces.

Photon Linear Polarization Coefficient of the Radiative Capture Process 2H(p, γ)3He at Thermal Energies

The photon polarization parameter of the proton-deuteron radiative capture process at thermal proton energies is calculated up to leading order (LO), using pionless effective field theory (EFT). In order to make a comparative study of this model, we compare our results for the photon polarization parameter with the realistic Argonne v14(AV14) and Argonne v18(AV18) modern nucleon-nucleon potentials and Urbana IX or Tucson-Melbourne three-nucleon interactions. The theoretical description of the 2H(p, γ)3 He reaction at thermal energies is complicated by the presence of the Coulomb interaction. Only the s-wave capture contribution to the thermal energy of this reaction is calculated. Three-body currents give small but significant contributions to some of the observables in the proton-deuteron radiative capture cross section at thermal neutron energies. Our result is in good agreement with the available experimental data and potential models' calculation at this order.

Systematic study of direct neutron capture

The direct neutron capture reaction is investigated within the potential model. All allowed electric dipole (E1), electric quadrupole (E2), and magnetic dipole (M1) transitions are taken into account. The nuclear structure ingredients involved in the calculation are determined from experimental data whenever available, and if not, from global microscopic nuclear models. A special emphasis is put on the excitation spectrum deduced from a mean field plus combinatorial model of nuclear level densities. It is shown that considering either a total intrinsic nuclear level density or one-particle, one-hole neutron excitations give rise to similar predictions provided the corresponding average spectroscopic factor is renormalized. The potential model is shown to provide a fair agreement between the predicted radiative neutron capture cross section and experimental data for light targets as well as with previous calculations. A systematic study for about 6400 nuclei with 8

Radiative neutron capture on carbon-14 in effective field theory

The cross section for radiative capture of neutron on carbon-14 is calculated using the model-independent formalism of halo effective field theory. The dominant contribution from $E1$ transition is considered, and the cross section is expressed in terms of elastic-scattering parameters of the effective-range expansion. Contributions from both resonant and nonresonant interaction are calculated. Significant interference between these leads to a capture contribution that deviates from a simple Breit-Wigner resonance form.

Radiative capture reactions with the participation of weakly bound light nuclei

Reactions of radiative capture of weakly bound light nuclei are investigated in the scope of the potential model. The applicability of the approach is demonstrated with an analysis of the cross section for the 6Li(p, γ)7Be reaction. Good agreement with the available experimental data is shown. The radiative capture cross section for the 6He(p, γ)7Li reaction in the region of low sub-barrier energies is evaluated. It is concluded that reactions involving 6He could also play a noteworthy part in stellar nucleosynthesis processes.

Large-scale continuum random-phase approximation predictions of dipole strength for astrophysical applications

Large-scale calculations of the E1 strength are performed within the random phase approximation (RPA) based on the relativistic point-coupling mean field approach in order to derive the radiative neutron capture cross sections for all nuclei of astrophysical interest. While the coupling to the single-particle continuum is taken into account in an explicit and self-consistent way, additional corrections like the coupling to complex configurations and the temperature and deformation effects are included in a phenomenological way to account for a complete description of the nuclear dynamical problem. It is shown that the resulting E1-strength function based on the PCF1 force is in close agreement with photoabsorption data as well as the available experimental E1 strength data at low energies. For neutron-rich nuclei, as well as light neutron-deficient nuclei, a low-lying so-called pygmy resonance is found systematically in the 5-10 MeV region. The corresponding strength can reach 10% of the giant dipole strength in the neutron-rich region and about 5% in the neutron-deficient region, and is found to be reduced in the vicinity of the shell closures. Finally, the neutron capture reaction rates of neutron-rich nuclei is found to be about 2-5 times larger than those predicted on the basis of the nonrelativistic RPA calculation and about a factor 50 larger than obtained with traditional Lorentzian-type approaches.

Exclusive breakup of17F on58Ni and208Pb within the continuum-discretized coupled-channels method

An analysis of the elastic and exclusive breakup of ${}^{17}$F on ${}^{58}$Ni and ${}^{208}$Pb targets is presented. The study is undertaken using the continuum-discretized coupled-channels (CDCC) method, assuming a core+valence model for the ${}^{17}$F projectile. The results are compared with recent data published for these reactions [Phys. Lett. B 681, 22 (2009)]. The calculations show that the exclusive breakup cross sections contain contributions from high multipoles, as well as a complicated interplay between Coulomb and nuclear couplings. This makes it difficult to extract radiative capture cross sections or structure information from the analyzed data.