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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Updated systematics of intermediate-energy single-nucleon removal cross sections

The body of experimental measurements of intermediate-energy reactions that remove a single nucleon from a secondary beam of neutron- or proton-rich nuclei continues to grow. These data have been analyzed consistently using an approximate, eikonal-model treatment of the reaction dynamics combined with appropriate shell-model descriptions of the projectile initial state, the bound final states spectrum of the reaction residue, and single-particle removal strengths computed from their wave-function overlaps. Here, the systematics of the ratio R s of the measured inclusive cross section to all bound final states and the calculated cross section to bound shell-model states—in different regions of the nuclear chart and involving both very weakly bound and strongly bound valence nucleons—is important in relating the empirically deduced orbital occupancies to those from the best available shell-model predictions. Importantly, several new higher-energy measurements, for which the sudden-approximation aspect of the dynamical description is placed on an even stronger footing, now supplement the previously analyzed measurements. These additional data sets are discussed. Their R s values are shown to conform to and reinforce the earlier-observed systematics, with no indication that the approximately linear reduction in R s with increasing nucleon separation energy is a consequence of a breakdown of the sudden approximation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Inclusive breakup cross sections in reactions induced by the nuclides 6 He and 6,7 Li in the two-body cluster model

Calculations of inclusive α particle production are performed to interpret reaction experimental data induced by the two-neutron halo 6He and the isotopes 6,7 Li on different target nuclei. In this work, we have implemented the zero-range post-form DWBA to compute the elastic and nonelastic breakup cross sections. Integrated cross sections, angular distributions and spectra are presented. Projectiles are approximated as two-body clusters, namely 6 He as α+dineutron and 6 Li ( 7 Li) are interpreted as α+deuteron(triton). The São Paulo optical potential is employed in the calculation of the distorted wave functions for the incident channels, while standard phenomenological interactions are taken for the fragment-target interactions. Calculations for 6 Li and 7 Li furnish a good description of the data, while the reaction involving 6 He is found to be more complicated, where interpretation of the data must still be considered incomplete. The present analysis identifies an overall large contribution from inclusive breakup emission for all the cases studied.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Heavy-ion fusion cross section formula and barrier height distribution

Methods for obtaining fusion cross section formulas are discussed, especially for those that take on an empirical form. A new expression starting with σ( E) = $\frac{1}{E}$ $\int ^{E}_{E_0}$ $(\int^{E'}_{E_0} B (E^\shortparallel) dE^\shortparallel)dE'$ has been explored. Here, B(E) is a reasonable, assumed function of the barrier height distribution, $\frac{d^2 (\sigma E)}{dE^2}$. Further, the resulting analytic cross section formula reproduces very well the excitation functions for many light and heavy fusion systems across wide energy ranges, when B(E) is assumed to be a multi-Gaussian function. This study offers an improved determination of the fusion barrier height distribution over other numerical techniques.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Absolute cross section of the C 12 ( p , γ ) N 13 reaction

Solar neutrino measurements have recently reached a level of sensitivity such that CNO fluxes can now be experimentally determined. While these first measurements are still only sensitive to the higher energy neutrinos resulting from the β + decays of 15 Ο produced by the 14 Ν ⁡( p ,$\gamma$)⁢ 15 O reaction, future measurements will work towards detection of neutrinos from the β + decay of 13 N from the 12 C ⁡( p ,$\gamma$)⁢ 13 N reaction. Here, this paper reports on a recent measurement of the 12 C ⁡( p ,$\gamma$)⁢ 13 N reaction covering a broad laboratory energy range between 1.0 and 2.5 MeV. The measurement was made to better determine the overall normalization of the absolute cross section and to explore the interference effects between the two broad, overlapping resonances at proton energies of 0.460 and 1.689 MeV and the direct capture to the ground state of 13 N in the framework of a multichannel R -matrix analysis. This work takes into account previous radiative capture as well as elastic 12 C ( p , p ) 12 C scattering data, making uncertainty estimations using a Bayesian framework, to determine a reliable extrapolation of the low energy S factor towards the stellar energy range of CNO hydrogen burning. These new experimental results, and a detailed investigation of the past literature data, suggest that the resonant component of the cross section should be 30% lower than previously accepted.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Direct cross-section measurement of the weak r -process Sr 88 ( α , n ) Zr 91 reaction in ν -driven winds of core-collapse supernovae

About half of the heavy elements beyond iron are known to be produced by the rapid neutron capture process, known as the r process. However, the astrophysical site producing the r process is still uncertain. Chemical abundances observed in several cosmic sites indicate that different mechanisms should be at play. For instance, the abundances around silver measured in a subset of metal-poor stars indicate the presence of a weak r process. This process may be active in neutrino-driven winds of core collapse supernovae where (α,n) reactions dominate the synthesis of Ζ ≈ 40 elements in the expelled materials. Scarcely measured, the rates of (α,n) reactions are determined from statistical Hauser-Feshbach calculations with α-optical-model potentials, which are still poorly constrained. Further, the uncertainties of the (α,n) reaction rates therefore make a significant contribution to the uncertainties of the abundances determined from stellar modeling. In this work, the 88 Sr (α,n)⁢ 91 Zr reaction which impacts the weak r-process abundances has been probed at astrophysics energy for the first time; directly measuring the total cross sections at astrophysical energies of 8.37–13.09 MeV in the center of mass (3.8–7.5 GK). Two measurements were performed at ATLAS with the electrically segmented ionization chamber MUSIC, in inverse kinematics, while following the active target technique. The cross sections of this α-induced reaction on 88 Sr, located at the shell closure N = 50, have been found to be lower than expected, by a factor of 3, despite recent statistical calculations validated by measurements on neighboring nuclei. This result encourages more experimental investigations of (α,n) reactions, at Ν = 50 and towards the neutron-rich side, to further test the predictive power and reliability of such calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Constraining calculations of Pu 239 ( n , γ ) cross sections with multistep cascade γ -ray spectra measured at the DANCE facility

Measurements of multistep cascade gamma-ray spectra from several low-lying 1 + resonances in the Pu 239 ( n , γ ) reaction were made using the DANCE detector. The measured spectra are compared to spectra simulated using several models for the photon strength function and the nuclear level density, representing the first analysis of this nature on a fissile nucleus. In general, models of the photon strength function that included a strong M 1 “scissors mode” contribution coupled with a Gilbert-Cameron nuclear level density provided a reasonable description of the spectra. Simulations using photon strength functions and nuclear level densities specifically for Pu 240 , extracted by the Oslo method, resulted in a very good representation of the measured spectra. Neutron-capture cross section calculations that included the scissors mode provided a good estimate of the previously measured values, without additional normalization. However, the scissors-mode energy that produced the best description of the multistep cascade spectra was different from the value that best reproduced the capture cross section. In addition, the 〈 Γ γ 〉 inferred from the multistep cascade calculations was somewhat less than the tabulated value, which was determined from resonance analysis. Published by the American Physical Society 2025

Ullmann, J. L. (ORCID:0000000207784405)↗
DOE OSTI2015

Cross section measurements for neutron inelastic scattering and the ( n , 2 n γ ) reaction on Pb 206

We measured excitation functions for γ production associated with the neutron inelastic scattering and the (n, 2n) reactions on 206 Pb from threshold up to 18 MeV for about 40 transitions. Two independent measurements were performed using different samples and acquisition systems to check consistency of the results. Moreover, the neutron flux was determined with a 235 U fission chamber and a procedure that were validated against a fluence standard. For incident energy higher than the threshold for the first excited level and up to 3.5 MeV, estimates are provided for the total inelastic and level cross sections by combining the present γ production cross sections with the level and decay data of 206 Pb reported in the literature. The uncertainty common to all incident energies is 3.0% allowing overall uncertainties from 3.3% to 30% depending on transition and neutron energy. Finally, the present data agree well with earlier work, but significantly expand the experimental database while comparisons with model calculations using the talys reaction code show good agreement over the full energy range.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Isotopic molybdenum total neutron cross section in the unresolved resonance region

Accurate isotopic molybdenum nuclear data are important because molybdenum can exist in nuclear reactor components including fuel, cladding, or as a high yield fission product. High-resolution time-of-flight neutron transmission measurements on highly enriched isotopic metallic samples of 95 Mo, 96 Mo, 98 Mo, and 100 Mo were performed in the resonance energy range from 1 to 620 keV. The measurements were taken with the newly developed modular 6 Li-glass transmission detector positioned at the 100-m experimental flight station. For the unresolved energy region (URR), new comprehensive methods of analysis were developed and validated in order to obtain accurate neutron total cross-section data from the measurement by correcting for background and transmission enhancement effects. Average parameters and fits to the total cross section for 95 Mo were obtained using the Hauser-Feshbach statistical model code FITACS, which is currently incorporated into the SAMMY code. Moreover, fits to the experimental data deviate from the current evaluated nuclear data file/B-VII.1 isotopic Mo evaluations by several percent in the URR.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

Inelastic neutron scattering cross sections for Ge 76 relevant to background in neutrinoless double- β decay experiments

The experimental signature in searches for the neutrinoless double- decay of 76 Ge is a peak near 2039 keV in the spectrum. Given the low probability of the process, it is important that the background in this region be well understood. Moreover, inelastic scattering reactions with neutrons from muon-induced interactions and ( ,n) reactions in the surrounding materials or in the detector can provide contributions to the background. We also measured the production cross sections for rays from the 76 Ge(n,n ) reaction in the 2039-keV region at incident neutron energies up to 4.9 MeV. In addition to determining that the cross sections of a previously known 2040.7-keV ray from the 3952-keV level in 76 Ge are rather small, we find that a larger contribution arises from a 2037.5-keV ray which is attributed to a newly identified level at 3147 keV in 76 Ge. Finally, a third contribution is also possible from another new level at 3577 keV. These results indicate that the 2039-keV region in 76 Ge neutrinoless double- decay searches is more complex than was previously thought.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

A reanalysis of radioisotope measurements of the $^9$Be$(\gamma,n)^8$Be cross-section

The $^9$Be$(\gamma,n)^8$Be reaction is enhanced by a near threshold $1/2^+$ state. Contradictions between existing measurements of this reaction cross-section affect calculations of astrophysical r-process yields, dark matter detector calibrations, and the theory of the nuclear structure of $^9$Be. Select well-documented radioisotope $^9$Be$(\gamma,n)$ source yield measurements have been reanalyzed, providing a set of high-accuracy independently measured cross sections. A Breit-Wigner fit of these corrected measurements yields $E_R=1738.8\pm1.9$ keV, $\Gamma_\gamma=0.771\pm0.021$ eV, and $\Gamma_n=268\pm15$ keV for the $1/2^+$ state. A virtual $1/2^+$ state is excluded with 99.3\% confidence.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Corrections to nucleon capture cross sections computed in truncated Hilbert spaces

Nucleon capture cross sections enter various astrophysical processes. Here, the measurement of proton capture on nuclei at astrophysically relevant low energies is a challenge, and theoretical computations in this long-wavelength regime are sensitive to the long-distance asymptotics of the wave functions. A theoretical foundation for estimating and correcting errors introduced in capture cross sections due to Hilbert space truncation has so far been lacking. We derive extrapolation formulas that relate the infrared regularized capture amplitudes to the infinite basis limit and demonstrate their efficacy for proton-proton fusion. Our results are thus relevant to current calculations of few-body capture reactions such as proton-proton fusion or proton capture on the deuteron, and they also open the way for the use of ab initio many-body wave functions represented in finite Hilbert spaces in precision calculations of nucleon capture on heavier nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

La 137 , 138 , 139 ( n , γ ) cross sections constrained with statistical decay properties of La 138 , 139 , 140 nuclei

The nuclear level densities and γ-ray strength functions of 138,139,140 La were measured using the 139 La( 3 He,α), 139 La( 3 He,' 3 He), and 139La(d,p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A~140 region is discussed. The 137,138,139 La(n,γ) cross sections were calculated at s- and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. As a result, good agreement is found between 139 La(n,γ) calculated cross sections and previous measurements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Measurement of the Bi 209 ( n , 4 n ) Bi 206 and Tm 169 ( n , 3 n ) Tm 167 cross sections between 23.5 and 30.5 MeV relevant to reaction-in-flight neutron studies at the National Ignition Facility

At the National Ignition Facility, experiments are being performed to measure charged-particle stopping powers in the previously unexplored warm dense plasma regime. These measurements are done using reaction-in-flight (RIF) neutrons from an inertial confinement fusion system. RIF neutrons are produced with a continuum of energies up to 30 MeV. By making activation measurements utilizing threshold reactions for neutrons in the energy range of 15 < E n < 30 MeV , the number of RIF neutrons can be determined and from this the stopping power of the deuterium and tritium ions that produced the RIF neutrons can be inferred. Currently, the 169 Tm ( n , 3 n ) 167 Tm reaction has been used. However, in an effort to provide a secondary complimentary measurement, efforts are underway to make use of the 209 Bi ( n , 4 n ) 206 Bi reaction, with a threshold of 22.5 MeV. The cross sections were measured at the 10 MV tandem Van De Graaff accelerator at the Triangle Universities Nuclear Laboratory with quasimonoenergetic neutrons between 23.5 and 30.5 MeV, where few previous measurements have been made. Cross-section data are compared to calculations and other available measurements.

42 ENGINEERING↗
DOE OSTI2017

Extraction of t slopes from experimental γ p → K + Λ and γ p → K + Σ 0 cross section data

Here, we analyze recent K + meson photoproduction data from the CLAS collaboration for the reactions γp → K + Λ and γp → K + Σ 0 , fitting measured forward-angle differential cross sections to the form AeBt. We develop a quantitative scheme for determining the kinematic region where the fit is to be done, and, from the extracted t-slope B, determine whether single-Reggeon exchange can explain the production mechanism. We find that, in the region 5 < s < 8.1 GeV 2 , production of the K + Λ channel can be explained by single K + Reggeon exchange, but the K + Σ 0 production channel cannot. We verify these conclusions by fitting the data to a differential cross section produced by the interfering sum of two exponential amplitudes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Proton capture reaction cross section measurements on Er 162 as a probe of statistical model calculations

It is crucial to measure reaction cross sections relevant to the astrophysical γ process so that theoretical reaction rates can be tested and validated with experimental data. Here, the total cross sections for the 162 Er(p,γ) 163 Tm and the 162 Er(p,n) 162 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 Er is the heaviest p nuclide to be measured by the activation method using γ -ray spectroscopy, so far. It is important to note that the energy range for the (p,γ) 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 Er 2 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.

150 ≤ A ≤ 189↗
DOE OSTI2018

First measurement of the Ti ( e , e ' ) X cross section at Jefferson Lab

To probe CP violation in the leptonic sector using GeV energy neutrino beams in current and future experiments using argon detectors, precise models of the complex underlying neutrino and antineutrino interactions are needed. The E12-14-012 experiment at Jefferson Lab Hall A was designed to perform a combined analysis of inclusive and exclusive electron scatterings on both argon (N = 22) and titanium (Z = 22) nuclei using GeV-energy electron beams. The measurement on titanium nucleus provides essential information to understand the neutrino scattering on argon, large contribution to which comes from scattering off neutrons. Here we report the first experimental study of electron-titanium scattering as double-differential cross section at beam energy E = 2.222 GeV and electron-scattering angle θ = 15.541°, measured over a broad range of energy transfer, spanning the kinematical regions in which quasielastic scattering and delta production are the dominant reaction mechanisms. In conclusion, the data provide valuable new information needed to develop accurate theoretical models of the electromagnetic and weak cross sections of these complex nuclei in the kinematic regime of interest to neutrino experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Dipole strength distribution in Pb 206 for the evaluation of the neutron capture cross section of Pb 205

The dipole strength distribution of 206 Pb was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced with an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 88 states resonantly excited at energies from 3.7 to 8.2 MeV. The analysis of the measured γ-ray spectra includes the quasicontinuum of levels at high energy. Monte Carlo simulation of γ-ray cascades were performed to obtain the intensities of inelastic transitions and branching ratios of the ground-state transitions. The extracted photoabsorption cross section shows enhanced dipole strength at the excitation energies around 5.5 and 7 MeV, which may related to a pygmy dipole resonance. Here, the present (γ,γ') data combined with (γ,n) data from the literature were used for confining input parameters of the statistical calculation code CCONE to derive the neutron-capture cross section of the unstable 205 Pb nucleus.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Realistic spectral function model for charged-current quasielastic-like neutrino and antineutrino scattering cross sections on C 12

A detailed study of charged current quasielastic neutrino and antineutrino scattering cross sections on a 12 C target with no pions in the final state is presented. The initial nucleus is described by means of a realistic spectral function S($p$,E) in which nucleon-nucleon correlations are implemented by using natural orbitals through the Jastrow method. The roles played by these correlations and by final-state interactions are analyzed and discussed. The model also includes the contribution of weak two-body currents in the two-particle two-hole sector, evaluated within a fully relativistic Fermi gas. The theoretical predictions are compared with a large set of experimental data for double-differential, single-differential, and total integrated cross sections measured by the MiniBooNE, MINER ν A , and T2K experiments. Good agreement with experimental data is found over the whole range of neutrino energies. The results are also in global good agreement with the predictions of the superscaling approach, which is based on the analysis of electron-nucleus scattering data, with only a few differences seen at specific kinematics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗