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Results for “Unstable nuclei induced nuclear reactions”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Examination of the sensitivity of quasifree reactions to details of the bound-state overlap functions

It is often stated that heavy-ion nucleon knockout reactions are mostly sensitive to the tails of the bound-state wave functions. In contrast, (p,2p) and (p,pn) reactions are known to access information on the full overlap functions within the nucleus. We analyze the oxygen isotopic chain and explore the differences between single-particle wave functions generated with potential models, used in the experimental analysis of knockout reactions, and ab initio computations from self-consistent Green's function theory. Contrary to common belief, we find that not only the tail of the overlap functions, but also their internal part is assessed in both reaction mechanisms, which are crucial to yield accurately determined spectroscopic information.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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 OSTI2020

Search for the high-spin members of the α : 2 n : α band in 10 Be

Clustering plays an important role in the structure of 10 Be. Exotic molecular-like configurations, such as α:2n:α, have been suggested at relatively low excitation energies. To search for the high-spin states that may belong to the molecular-like α:2n:α configuration in 10 Be. Measuring excitation functions for 6 He + α scattering, populating states in the excitation energy range from 4.5 MeV to 8 MeV in 10 Be using a 6 He rare-isotope beam and a thick helium gas target. No new excited states in 10 Be have been observed. Stringent limitation on the possible degree of a-clustering of the hypothetical yrast 6 + state has been obtained. Here, the high-spin members of the α:2n:α molecular-like rotational band configuration, that is considered to have a 0 + bandhead at 6.18 MeV, either do not exist or have small overlap with the 6 He(g.s.)+α channel.

6 ≤ A ≤ 19↗
DOE OSTI2024

First study of the $^{139}\text{Ba}(n,y)^{140}\text{Ba}$ reaction to constrain the conditions for the astrophysical $\mathcal{i}$ process

New astronomical observations point to a nucleosynthesis picture that goes beyond what was accepted until recently. The intermediate “i” process was proposed as a plausible scenario to explain some of the unusual abundance patterns observed in metal-poor stars. The most important nuclear physics properties entering i-process calculations are the neutron-capture cross sections and they are almost exclusively not known experimentally. In this report we provide the first experimental constraints on the 139 Ba(n,γ) 140 Ba reaction rate, which is the dominant source of uncertainty for the production of lanthanum, a key indicator of i-process conditions. This is an important step towards identifying the exact astrophysical site of stars carrying the i-process signature.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Experimental study of the 24 Na m ( d,p ) 25 Na reaction and implications for the influence of the 24 Al m isomer on rp -process nucleosynthesis

A radioactive beam of 24 Na with 90% of its content in its 1 + isomeric state (E ex = 0.472 MeV, t 1/2 = 20.18 ms) has been developed and used to perform a measurement of the 24 Na m ( d,p ) 25 Na reaction at the John D. Fox Accelerator Laboratory at Florida State University. This reaction selectively populated ℓ = 0 transfers, allowing the study of low-spin states in 25 Na. Mirror symmetry arguments were then used to investigate the effects of the isomeric state of 24 Al (E ex = 0.426 MeV, t 1/2 = 130 ms) on the astrophysical rate of the 24 Al m (p,γ) 25 Si reaction. Experimental parameters were extracted to provide, for the first time, an experimental reaction rate for the destruction of 24 Al via proton captures in its isomeric state relevant to rp-process nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Spectroscopy of 13 Be through isobaric analog states in 13 B

Spectroscopy of the exotic, neutron-unbound beryllium isotope, 13 Be, is still a puzzle despite significant experimental efforts. To observe T = 5/2 states in 13 B, establish spin parities and spectroscopic factors, and use isospin symmetry to inform spectroscopy of 13 Be, excitation functions for resonance elastic scattering of 12 Be on protons were measured in the c.m. energy range from 1 MeV to 5 MeV. Two T = 5/2 states in 13 B at excitation energies 18.25 MeV and 19.95 MeV were observed. Unambiguous 1/2 + and 5/2 + spin-parity assignments were made, and spectroscopic factors were established using R-matrix analysis of the measured 12 Be + p excitation functions. Here, we provide the first direct and unambiguous spin-parity assignments and spectroscopic factor measurements for the resonances in the A = 13, T = 5/2 isobaric multiplet. This puts us on a solid footing to identify the 2.3 MeV state in 13 Be as 5/2 + and infer the existence of an s-wave (1/2 + ) resonance at around 0.6 MeV with a relatively small spectroscopic factor.

6 ≤ A ≤ 19↗
DOE OSTI2021

Assessing the impact of valence sd neutrons and protons on fusion

Experimental near-barrier fusion cross sections for 17 F + 12 C are compared to the fusion excitation functions for 16,17,18 O, 19 F, and 20 Ne ions on a carbon target. Normalized or reduced fusion cross sections are utilized in order to compare the different systems and account for the differing static size of the incident ions as well as changes in fusion barrier. Fusion excitation functions for the case of the mirror nuclei 17 F and 17 O with a single sd nucleon are compared. The 17 F data are also juxtaposed with nuclei involving multiple sd nucleons. Trends of the fusion cross section above the barrier beyond the expected systematic behavior are observed. These trends are interpreted as the interplay of the sd protons and neutrons. Furthermore, the experimental data are also compared to a widely used analytic model of near-barrier fusion, a time-dependent Hartree-Fock model, and coupled channels calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Impact of shell structure on the fusion of neutron-rich mid-mass nuclei

The influence of shell effects on fusion of mid-mass nuclei is explored using isotopic chains of K and Ar ions on an oxygen target. Comparison of the reduced excitation functions reveals that the fusion cross section for the open neutron-shell projectile nuclei 41 K and 45 K is systematically larger than for the closed neutron-shell projectiles 39 K and 47 K. Furthermore, the São Paulo fusion model using matter densities from systematics fails to describe the measured excitation functions. Use of more realistic densities from a Dirac-Hartree-Bogoliubov (DHB) approach performs significantly better though it still overpredicts the closed-shell nuclei.

39 ≤ A ≤ 58↗
DOE OSTI2023

β + Gamow-Teller Strengths from Unstable 14 O via the (d, 2 He) Reaction in Inverse Kinematics

For the first time, the (d, 2 He) reaction was successfully used in inverse kinematics to extract the Gamow-Teller transition strength in the β + direction from an unstable nucleus. The new technique was made possible by the use of an active-target time-projection chamber and a magnetic spectrometer, and opens a path to addressing a range of scientific challenges, including in astrophysics and neutrino physics. Here, in this Letter, the nucleus studied was 14 O, and the Gamow-Teller transition strength to 14 N was extracted up to an excitation energy of 22 MeV. The data were compared to shell-model and state-of-the-art coupled-cluster calculations. Shell-model calculations reproduce the measured Gamow-Teller strength distribution up to about 15 MeV reasonably well, after the application of a phenomenological quenching factor. In a significant step forward to better understand this quenching, the coupled-cluster calculation reproduces the full strength distribution well without such quenching, owing to the large model space, the inclusion of strong correlations, and the coupling of the weak interaction to two nucleons through two-body currents.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Extraction of the non-spin- and spin-transfer isovector responses via the 12 C ⁡( 10 Be, 10 B + 𝛾)⁢ 12 B reaction

The isovector response in 12 B was investigated via the 12 C ⁡( 10 Be, 10 B + 𝛾)⁢ 12 B* reaction at 100⁢𝐴MeV. By utilizing the 𝛾-decay properties of the 1.74 MeV 0 + and 0.718 MeV 1 + states in 10 B, the separate extraction of the non-spin-transfer (Δ⁢𝑆 = 0) and spin-transfer (Δ⁢𝑆 = 1) isovector responses up to an excitation energy of 50 MeV in 12 B in a single measurement is demonstrated. The experimental setup employed the S800 spectrometer to detect and analyze the 10 B ejectiles and the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) for obtaining the Doppler-reconstructed spectrum for 𝛾 rays emitted in flight by 10 B. A 12 C foil was placed at the pivot point of the spectrograph. Here, the 12 B reaction product was not detected. Contributions from transitions associated with the transfer of different units of angular momentum in the non-spin- and spin-transfer responses were analyzed using a multipole decomposition analysis. The extracted non-spin-dipole (Δ⁢𝑆 = 0, Δ⁢𝐿 = 1) and spin-dipole (Δ⁢𝑆 = 1, Δ⁢𝐿 = 1) responses were found to be consistent with available data from other charge-exchange probes, validating the non-spin- and spin-transfer filters used. While statistical uncertainties and experimental resolutions were relatively large due to the modest intensity of the 10 Be secondary beam, the results show that, with the much higher intensities that will be available at new rare-isotope beam facilities, the ( 10 Be, 10 B + 𝛾) reaction and its Δ⁢𝑇 𝑧 = −1 partner, the ( 10 C, 10 B + 𝛾) reaction, are powerful tools for elucidating the isovector non-spin- and spin-transfer responses in nuclei.

Charge-exchange reactions↗
DOE OSTI2020

Determination of the cluster-decay branching ratio from a near-threshold molecular state in Be10

A puzzle has long existed for the α-cluster content in the near-threshold 7.54-MeV state of 10Be. A new measurement was conducted to measure the cluster-decay partial width of this state using the reaction 9 Be( 9 Be, 10 B *→α+ 6 He) 8 Be at 45-MeV beam energy. Special measures were taken to reduce the strong near-threshold background. Additionally, the neutron-decay strength was also obtained based on the threefold coincident measurement. A cluster-decay branching ratio of ( 4.04 ± 1.26 ) × 10 -4 is obtained, resulting in a reasonably large α -cluster spectroscopic factor. The present Rapid Communication confirms the formation of the σ -bond molecular rotational band headed by the 6.18-MeV state in 10 Be .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Observation of new neutron-rich isotopes in the vicinity of Zr 110

Neutron-rich radioactive isotope (RI) beams in the vicinity of 110 Zr were produced using the in-flight fission of a 345-MeV/nucleon 238 U beam at the RIKEN Radioactive Isotope Beam Factory. Here, the RI beams were separated in flight by the large-acceptance two-stage fragment separator BigRIPS. Isotopes were clearly identified in a low-background particle-identification plot, which was obtained from the measurements of time of flight, magnetic rigidity, and energy loss using beam-line detectors placed in the BigRIPS separator and the ZeroDegree spectrometer. Nine new isotopes, 101 Br, 102 Kr, 105,106 Rb, 108 Sr, 110,111 Y, 114 Zr, and 117 Nb, are reported for the first time, with their measured production cross sections compared with the extrapolations of lighter isotopes down to the femtobarn regime.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Proton Distribution Radii of 16–24 O: Signatures of New Shell Closures and Neutron Skin

The root mean square radii of the proton density distribution in 16–24 O derived from measurements of charge changing cross sections with a carbon target at ~900A MeV together with the matter radii portray thick neutron skin for 22–24 O despite 22,24 O being doubly magic. Imprints of the shell closures at N=14 and 16 are reflected in local minima of their proton radii that provide evidence for the tensor interaction causing them. The radii agree with ab initio calculations employing the chiral NNLO sat interaction, though skin thickness predictions are challenged. Furthermore, shell model predictions agree well with the data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Using spin alignment of inelastically excited nuclei in fast beams to assign spins: The spectroscopy of 13 O as a test case

Excited states in O 13 were investigated using inelastic scattering of an E / A = 69.5 MeV O 13 beam off of a Be 9 target. The excited states were identified in the invariant-mass spectra of the decay products. Both single-proton and sequential two-proton decays of the excited states were examined. Furthermore, for a number of the excited states, the protons were emitted with strong anisotropy where emissions transverse to the beam axis are favored. The measured proton-decay angular distributions were compared to predictions from distorted-wave Born-approximation calculations of the spin alignment which was shown to be largely independent of the excitation mechanism. The deduced O 13 level scheme is compared to ab initio no-core shell model with continuum predictions. The lowest-energy excited states decay isotropically consistent with predictions of strong proton 1 s 1 / 2 structure. Above these states in the level scheme, we observed a number of higher-spin states not predicted within the model. Possibly these are associated with rotational bands built on deformed cluster configurations predicted by antisymmetrized molecular dynamics calculations. The spin alignment mechanism is shown to be useful for making spin assignments and may have widespread use.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Single-nucleon knockout cross sections for reactions producing resonance states at or beyond the drip line

Single-nucleon knockout cross sections from fast secondary beams of the proton-drip-line nuclei 9 C, 13 O, and 17 Ne on a 9 Be target have been studied with emphasis on the production of resonance states. These states were identified by their invariant mass, and resonances with two-, three-, and five-body exit channels were examined. The measured cross sections for these states were compared with eikonal-model predictions using shell-model or variational Monte Carlo spectroscopic factors. The experimental yields were found to be suppressed relative to the model predictions, especially when a well-bound neutron or proton is removed. This suppression exceeds that found systematically in measured inclusive cross sections to particle-bound final states. In neutron knockout from 9 C and 13 O projectiles, this suppression of the unbound ground-state residuals yield is a factor of two to three times larger than that found in the bound final-state studies. Modifications to the structure of these systems due to coupling of the shell-model configurations to the continuum is expected to contribute to this extra suppression, especially when the final state is a near-threshold resonance. Furthermore, other considerations including the role of nuclear dynamics may be required to explain all the observed trends.

6 ≤ A ≤ 19↗
DOE OSTI2021

Spectroscopic factors in dripline nuclei

Single-nucleon knockout reaction studies of the proton-dripline nuclei 9 C and 13 O suggest an appreciable suppression of spectroscopic factors. In this work, we calculate the one-neutron and one-proton spectroscopic factors for the mirror pair 9 C – 9 Li and 13 O using two variants of the continuum shell model: the complex-energy Gamow shell model and the real-energy shell model embedded in the continuum. Furthermore, our results indicate that the continuum effects strongly suppress the spectroscopic factors of well-bound orbits in the dripline systems but have less impact on the spectroscopic factors of weakly bound states.

6 ≤ A ≤ 19↗
DOE OSTI2021

In-beam γ-ray spectroscopy of 62,64 Cr

The region of neutron-rich Cr isotopes has garnered much attention in recent years due to a rapid onset of collectivity near neutron number N = 40. We report here on the first γ-ray spectroscopy beyond the ($4$ $^{+}_{1}$) state in 62,64 Cr, using nucleon removal reactions from several projectiles within a rare-isotope beam cocktail. A candidate for the 6 + state in 64 Cr is presented as well as one for, possibly, the second excited 0 + state in 62 Cr. The results are discussed in comparison to the LNPS shell-model predictions that allow for neutron excitations across the N = 40 harmonic oscillator gap into the g 9/2 and d 5/2 orbitals. Here, the calculated level schemes for 62,64 Cr reveal intriguing collective structures. From the predicted neutron particle-hole character of the low-lying states in these Cr isotopes, 62 Cr emerges as a transitional system on the path to the center of the N = 40 island of inversion.

59 ≤ A ≤ 89↗