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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Sensitivity of the 13 C(α,n) 16 O S factor to the uncertainty in the level parameters of the near-threshold state

The 13 C(α,n) 16 O reaction is the main source of neutrons for the s and i processes in asymptotic giant branch stars and carbon-enhanced metal-poor stars, respectively. The reaction rate over the relevant temperature range from 0.1 to 0.3 GK translates into a center-of-mass energy range of 150 to 540 keV. Current measurements extend down to 300 keV, still requiring an extrapolation of the cross section. At these low energies, the high-energy tail of a 1/2 + state near the reaction threshold makes a significant contribution to the cross section, but its amplitude is still highly uncertain. In this work the uncertainties associated with the low-energy cross-section extrapolation are investigated, in particular the sensitivity to the energy, width, and Coulomb renormalized asymptotic normalization coefficient of the near-threshold resonance. Furthermore, recently it has been suggested that the energy of the near-threshold level may have a large impact on the extrapolation, but this is not found to be the case compared with the other sources of uncertainty.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1978

Direct nuclear-pumped lasers using the He-3/n,p/H-3 reaction

A description is presented of experimental results concerning a specific class of direct nuclear-pumped lasers classified as 'volumetric nuclear lasers'. In the considered laser system a fissioning gas, He-3, is mixed with the lasing gas to form a homogeneous mixture, resulting in uniform volume excitation. In typical volumetric nuclear lasers a fast-burst reactor is used as a source of neutrons which penetrate a polyethylene moderator. Here the fast neutrons are thermalized. After thermalization, neutrons scatter into the laser cell. Nuclear reactions produce a proton of 0.56 MeV and a tritium ion of 0.19. These ions produce secondary electrons which pump the laser medium creating a population inversion. The results reported demonstrate direct nuclear pumping of He-3-Ar, Xe, Kr, and Cl with the considered system.

Deyoung, R. J.↗
DOE OSTI2023

Ab initio single-neutron spectroscopic overlaps in lithium isotopes

We calculate single-neutron spectroscopic overlaps for lithium isotopes in the framework of the ab initio symmetry-adapted no-core shell model. We report the associated neutron-nucleus asymptotic normalization coefficients (ANCs) and spectroscopic factors (SFs) that are important ingredients in many reaction cross-section calculations. While spectroscopic factors have been traditionally extracted from experimental cross sections, their sensitivity on the type of reactions, the energy, and the underlying models point to the need for determining SFs from first-principle structure considerations. As illustrative examples, we present 6 Li + n, 7 Li ⁢+ n, and 8 Li ⁢+ n, and we show that the results are in a good agreement with those of other ab initio methods, where available, including the quantum Monte Carlo approach. Here, we compare ANCs and SFs to available experimentally deduced values, with a view toward expanding this study to heavier nuclei and to extracting intercluster effective interactions for input into analyses of existing and future experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

First experiment at the Super Heavy Element Factory: High cross section of Mc 288 in the Am 243 + Ca 48 reaction and identification of the new isotope Lr 264

Here, we present results of the first experiment aimed at the synthesis of Mc isotopes in the 243 Am+ 48 Ca reaction performed at the new gas-filled separator DGFRS-2 online to the new cyclotron DC280 at the Super Heavy Element Factory at JINR. Fifty-five new decay chains of 288 Mc and six chains assigned to 289 Mc were detected. The α decay of 268 Db with an energy of 7.6–8.0 MeV, half-life of 16$^{+6}_{-4}$h, and a branch of 55$^{+20}_{-15}$% was registered for the first time, and a new spontaneously fissioning isotope 264 Lr with a half-life of 4.9$^{+2.1}_{-1.3}$h was identified. The cross section for the 243 Am( 48 Ca,3n) 288 Mc reaction was measured to be 17.1$^{+6.3}_{-4.7}$ pb, which is the largest value for the known superheavy nuclei at the island of stability.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

New 13 C(α,n) 16 O Cross Section with Implications for Neutrino Mixing and Geoneutrino Measurements

Precise antineutrino measurements are very sensitive to proper background characterization. Here, we present an improved measurement of the 13 C(α,n) 16 O reaction cross section which constitutes significant background for large v¯ detectors. We greatly improve the precision and accuracy by utilizing a setup that is sensitive to the neutron energies while making measurements of the excited state transitions via secondary γ-ray detection. Our results shows a 54% reduction in the background contributions from the 16 O(3–, 6.13 MeV) state used in the KamLAND analysis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

γ -ray spectroscopy of astrophysically important states in Ca 39

Background: Nova explosions synthesize elements up to A ≃ 40 , and discrepancies exist between calculated and observed abundances of Ar and Ca created in the explosion. The K 38 ( p , γ ) Ca 39 reaction rate has been illustrated to be influential on these isotopic abundances at the endpoint of nova nucleosynthesis. The energies of the three most important resonances, corresponding to J π = 5 / 2 + excited states in the Ca 39 nucleus above the proton separation threshold, are uncertain and one has been measured with conflicting values [ E r = 679 ( 2 ) versus E r = 701 ( 2 ) keV] in previous experiments. Purpose: Reducing the uncertainties on the resonance energies would allow for a better understanding of the reaction rate. To improve these uncertainties, we searched for γ rays from the depopulation of the corresponding excited states in Ca 39 . Methods: We report a new measurement of these resonance energies via the observation of previously unobserved γ -ray transitions. These transitions were observed by studying the Ca 40 ( 3 He , α γ ) Ca 39 reaction with Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies (GODDESS). The updated resonance energies were then used to calculate the K 38 ( p , γ ) Ca 39 reaction rate and assess its uncertainties. Results: In total, 23 new transitions were found, including three γ -ray transitions corresponding to the three J π = 5 / 2 + states of astrophysical interest at energies of 6156.2(16), 6268.8(22), and 6470.8(19) keV. These correspond to resonance energies in the K 38 ( p , γ ) Ca 39 reaction of 386(2), 498(2), and 701(2) keV. Conclusions: Updated K 38 ( p , γ ) Ca 39 reaction rate calculations reflect a reduced upper limit at nova temperatures. However, the lower-than-previously-measured energy of the 498-keV resonance and uncertainty in its resonance strength increases the upper limit of the rate close to previous estimates at 0.4 GK.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Alpha-decay width of a near proton-threshold resonance in the 7 Li( α, α ) channel

We investigate the alpha-decay width of a near proton-threshold resonance in 11 B by the excitation functions of 7 Li(α, α) and 7 Li(α, α’) reactions. This resonance is an example of loosely bound atomic nuclei, understood as small open quantum systems, that exhibit properties significantly influenced by their coupling to the continuum. The present experiment focuses on the formation of a specific state in 11 B at excitation energy in the region near 11.4 MeV by bombarding a 7 Li target with a 4 He beam at energies ranging from 3.92 to 4.56 MeV in the laboratory frame. The study provides data complementary to previous observations of the proton emission in the β-decay of the neutron-rich halo nucleus 11 Be. An R-matrix fit to the data provides resonance energy and partial widths consistent with J π =1/2 + for a narrow near-threshold state in 11 B at 11.400(20) MeV, that is 171(20) keV above the proton emission threshold, with partial α-decay width Γ α =2.5$^{+3.5}_{–1.5}$ keV in elastic scattering and Γ α' =15.8$^{+1.9}_{–0.4}$ keV in inelastic scattering. These findings contribute to the understanding of the structure of this open quantum system resonance.

11B↗
DOE OSTI2025

Constraining the 3He + 3He Gamow energy probed in high energy density plasmas at the National Ignition Facility

Polar-direct-drive implosions at the National Ignition Facility generated large plasma volumes to study the 3He + 3He fusion reaction. The ion temperature, which determines the Gamow peak energy, was constrained by isolating the thermal contribution to the D3He-proton spectral width in a 3He plasma doped with deuterium. X-ray penumbral imaging was used to measure electron temperature, density, and hotspot volume, which was subsequently used to model the spectral broadening from plasma stopping power. Results showed 30% of the D3He-proton spectral width was due to stopping power, with residual flows contributing ≈10%. The 3He temperature was determined as T3He = 12.4 ± 3.2 keV, corresponding to a Gamow energy of 95 ± 14 keV. These experiments achieved the lowest Gamow energy to date for studying 3He + 3He fusion in high energy density plasma, approaching conditions in the Sun.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Analog B ( M 1 ) strengths in the T z = ± 3 2 mirror nuclei Mn 47 and Ti 47

The lifetimes of the first excited 7 2 − states in the T z = ± 3 2 mirror nuclei Mn 47 and Ti 47 have been extracted utilizing the γ -ray line shape method, giving τ = 687 ( 36 ) ps and τ = 331 ( 15 ) ps respectively. Since these transitions are essentially pure M 1 transitions, these results allow for a high-precision comparison of analog M 1 strengths in mirror nuclei. The two analog B ( M 1 ) s are observed to be identical to a precision of about 10 % . The expected dependence of the transition matrix element with T z has been used to extract the separate isoscalar and isovector components of the transition strength, and the results are discussed in the context of predictions, based on the isospin formalism, regarding analog B ( M 1 ) strengths. Published by the American Physical Society 2024

39 ≤ A ≤ 58↗
DOE OSTI2025

Laser-initiated p – 11 B fusion reactions in petawatt high-repetition-rate laser facilities

Driving of the nuclear fusion reaction p + 11 B → 3α + 8.7 MeV under laboratory conditions by interaction between high-power laser pulses and matter has become a popular field of research, owing to its numerous potential applications: as an alternative to deuterium–tritium for fusion energy production, astrophysics studies, and alpha-particle generation for medical treatment. One possible scheme for laser-driven p– 11 B reactions is to direct a beam of laser-accelerated protons onto a boron (B) sample (the so-called “pitcher-catcher” scheme). This technique has been successfully implemented on large high-energy lasers, yielding hundreds of joules per shot at low repetition. We present here a complementary approach, exploiting the high repetition rate of the VEGA III petawatt laser at CLPU (Spain), aiming at accumulating results from many interactions at much lower energy, to provide better control of the parameters and the statistics of the measurements. Despite a moderate energy per pulse, our experiment allowed exploration of the laser-driven fusion process with tens (up to hundreds) of laser shots. The experiment provided a clear signature of the reactions involved and of the fusion products, accumulated over many shots, leading to an improved optimization of the diagnostics for experimental campaigns of this type. In this paper, we discuss the effectiveness of laser-driven p– 11 B fusion in the pitcher–catcher scheme, at a high repetition rate, addressing the challenges of this experimental scheme and highlighting its critical aspects. Our proposed methodology allows evaluation of the performance of this scheme for laser-driven alpha particle production and can be adapted to high-repetition-rate laser facilities with higher energy and intensity.

Alpha particles↗
DOE OSTI2021

Rapid extraction of short-lived isotopes from a buffer gas cell for use in gas-phase chemistry experiments, Part II: On-line studies with short-lived accelerator-produced radionuclides

We report a novel combination of advanced gas-chromatography and detection systems coupled to a buffer-gas cell was characterized on-line to allow gas-phase chemical studies of accelerator-produced short-lived α -decaying mercury, francium, and astatine isotopes. These were produced in 40 Ar- and 48 Ca-induced nuclear fusion–evaporation reactions, subsequently isolated in the recoil separators MARS at Texas A&M University, USA, and TASCA at GSI Darmstadt, Germany, before being thermalized in a buffer-gas-stopping cell. From the latter, the nuclear reaction products were extracted into gas-phase chromatographic systems, suitable for registering α-decaying short-lived radionuclides, such as isotopes of superheavy elements. Efficiencies of 21(3)% for 204-209 Fr were reached for the extraction into the optimized miniCOMPACT gas-chromatography setup, indicating that this technique enables the identification of isotopes of volatile as well as non-volatile elements. These studies guide the path towards chemical investigations of superheavy elements beyond flerovium, which are out of reach with currently used setups.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Isospin mixing and the cubic isobaric multiplet mass equation in the lowest T=2, A=32 quintet

The isobaric multiplet mass equation (IMME) is known to break down in the first T=2,A=32 isospin quintet. In this work we combine high-resolution experimental data with state-of-the-art shell-model calculations to investigate isospin mixing as a possible cause for this violation. The experimental data are used to validate isospin-mixing matrix elements calculated with newly developed shell-model Hamiltonians. Our analysis shows that isospin mixing with nonanalog T=1 states contributes to the IMME breakdown, making the requirement of an anomalous cubic term inevitable for the multiplet.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Superfast quarks in deuterium

An extension to our previous study on nuclear parton distribution functions (nPDFs) [Kim and Miller, Phys. Rev. C 106, 055202 (2022)] using light-front holographic quantum chromodynamics (LFHQCD) [Brodsky, de Teramond, Dosch, and Erlich, Phys. Rep. 584, 1 (2015)] is presented. We apply the effects of nucleon motion inside the nucleus (Fermi motion/smearing) to deuterium, extending our deuterium nPDFs to the superfast , 𝑥 > 1, region [Frankfurt and Strikman, Phys. Rep. 160, 235 (1988)] where we estimate our results to be reasonable up to 𝑥 ≈ 1.7. We utilize four different deuteron wave functions (AV18, NijmI, NijmII, Nijm93). We find that our model, with no additional new parameters, shows very good agreement with deuterium EMC ratio data obtained from the BONuS experiment [Fenker et al., Nucl. Instrum. Methods Phys. Res. A 592, 273 (2008); Baillie et al. (CLAS Collaboration), Phys. Rev. Lett. 108, 142001 (2012); Phys. Rev. Lett. 108, 199902(E) (2012); Tkachenko et al. (CLAS Collaboration), Phys. Rev. C 89, 045206 (2014); Phys. Rev. C 90, 059901(E) (2014); Griffioen et al., Phys. Rev. C 92, 015211 (2015)]. Looking beyond conventional nuclear physics, and in anticipation of 12 GeV experiments at Jefferson Lab, we use a LFHQCD ansatz to predict the contributions of an exotic six-quark state to the deuteron 𝐹 2 structure function, 𝐹$^D_2$, in the superfast region. We find that the effects of using other potentials are about the same magnitude as six-quark effects—both have small effects in 𝑥 < 1, but have significant contributions at 𝑥 > 1.

Physics↗
DOE OSTI2021

Search for in-band transitions in the candidate superdeformed band in Si 28

Background: Superdeformed (SD) bands are suggested by theory around Ca 40 and in lighter alpha-conjugate nuclei such as Mg 24 , Si 28 , and S 32 . Such predictions originate from a number of theoretical models including mean-field models and antisymmetrized molecular dynamics (AMD) calculations. While SD bands have been identified in Ca 40 and its near neighbors, evidence of their existence in the lighter, midshell nuclei is circumstantial at best. Additionally, the key evidence of superdeformation would be the observation of transitions with high B ( E 2 ) transition strengths connecting states in a rotational sequence. This is challenging information to obtain since the bands lie at a high excitation energy and competition from out-of-band decay is dominant. Purpose: The purpose of the present study is to establish a new methodology to circumvent the difficulties in identifying and quantifying in-band transitions through directly populating candidate states in the SD band in Si 28 through inelastic alpha scattering, selecting such states with a spectrometer, and measuring their gamma-ray decay with a large array of high-purity germanium detectors, allowing direct access to electromagnetic transition strengths. Methods: Excited states in Si 28 were populated in the Si 28 ( α , α ' ) reaction using a 130-MeV He 4 beam from the K140 AVF cyclotron at the Research Center for Nuclear Physics. Outgoing alpha particles were analyzed using the Grand Raiden spectrometer positioned at an angle of 9 . 1 ° to favor the population of states with J ≈ 4 . Coincident gamma rays were detected with the CAGRA array of 12 HPGe clover detectors augmented by a set of four large LaBr 3 detectors. Results: Data analysis showed that it was possible to identify additional low-energy transitions in competition with high-energy decays from excited states in Si 28 in the vicinity of 10 MeV. However, while the candidate 4 + SD state at 10.944 MeV was populated, a 1148-keV transition to the candidate 2 + SD state at 9.796 MeV was not observed, and only an upper limit for its transition strength of B ( E 2 ) < 43 W.u. could be established. This contradicts AMD predictions of ≈ 200 W.u. for such a transition. Conclusion: The present study strongly rejects the hypothesis that the candidate set of states identified in Si 28 represents an SD band, which demonstrates the potential of the methodology devised here.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗