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Langer, C.

Publications and source records attributed to Langer, C..

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Precise measurement of nuclear interaction cross sections towards neutron-skin determination with R 3 B

The R 3 B (Reactions with Relativistic Radioactive Beams) experiment as a major instrument of the NUSTAR collaboration for the research facility FAIR in Darmstadt is designed for kinematically complete studies of reactions with high-energy radioactive beams. Part of the broad physics program of R 3 B is to constrain the asymmetry term in the nuclear equation-of-state and hence improve the description of highly asymmetric nuclear matter (e.g., in neutron stars). For a precise determination of the neutron-skin thickness – an observable which is directly correlated with the symmetry energy in theoretical calculations – by measuring absolute fragmentation cross sections, it is essential to quantify the uncertainty and challenge the reaction model under stable conditions. During the successful FAIR Phase-0 campaign of R 3 B, we precisely measured the energy dependence of total interaction cross sections in 12 C + 12 C collisions, for a direct comparison with calculations based on the eikonal reaction theory.

Ponnath, L. (ORCID:0000000286742624)↗
DOE OSTI2024

β -delayed neutron emission of Mn 64 , Cr 62 , and Fe 65

The β-decay properties of nuclei near the second nuclear “island of inversion” around neutron rich nuclei with neutron number 40 are important tests of nuclear structure models and interactions. In particular, the β-delayed neutron emission branch (Ρ n ), is useful for investigating β-strength and neutron-γ competition above the neutron separation energies of the daughter nuclei. We report new constraints for Ρ n values for three nuclei in the region: 62 Cr (Ρ n <1%), 64 Mn (Ρ n = 1.5⁢(6)%), and 65 Fe (Ρ n < 1%), measured with the Neutron Emission Ratio Observer (NERO) neutron long counter system and the Beta Counting Station (BCS) at the National Superconducting Cyclotron Laboratory (NSCL). Our results resolve the large discrepancy between previous direct and indirect measurements for 64 Mn and confirm the predictions of global theoretical models when a statistical treatment of the γ and neutron decays of the daughter states is included. Here we also obtain improved half-lives for 62 Cr [206(5) ms] and the short-lived isomer in the 62 Fe daughter [112(7) ms] from β-delayed γ emission data obtained in the same experiment with the Summing NaI (SuN) total absorption spectrometer. Finally, we use γ emission data to obtain a new upper limit for the 62 Cr β-decay population of the long-lived isomeric state in 62 Mn.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Measurement of nuclear interaction cross sections towards neutron-skin thickness determination

The accuracy of reaction theories used to extract properties of exotic nuclei from scattering experiments is often unknown or not quantified, but of utmost importance when, e.g., constraining the equation of state of asymmetric nuclear matter from observables as the neutron-skin thickness. In order to test the Glauber multiple-scattering model, the total interaction cross section of 12 C on carbon targets was measured at initial beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The measurements were performed during the first experiment of the newly constructed R 3 B (Reaction with Relativistic Radioactive Beams) experiment after the start of FAIR Phase-0 at the GSI/FAIR facility with beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The combination of the large-acceptance dipole magnet GLAD and a newly designed and highly efficient Time-of-Flight detector enabled a precise transmission measurement with several target thicknesses for each initial beam energy with an experimental uncertainty of ±0.4%. A comparison with the Glauber model revealed a discrepancy of around 3.1% at higher beam energies, which will serve as a crucial baseline for the model-dependent uncertainty in future fragmentation experiments.

Astronomy & Astrophysics↗
DOE OSTI2024

New insight into knockout reactions from the two-proton halo nucleus 17 Ne

The unexplained disagreement in the dependence of spectroscopic factors (𝐶2⁢𝑆 exp ) on the binding energy obtained by nucleon knockout using different targets is still a puzzle that needs to be addressed. To find an explanation of this riddle through exclusive measurements using different targets. The exclusive measurements were performed by using a 17 Ne beam with an energy of 500 MeV/u incident on C and CH 2 targets. Through the standard theoretical approach, 𝐶 2⁢ 𝑆 exp were derived from the analysis of the experimental data on proton ejection from the proton halo in 17 Ne as well as from its core 15 O. For the C target, proton ejection from the proton halo gave 𝐶 2 ⁢𝑆 exp about 37% smaller than for the H target. But when protons are ejected from the core of 17 Ne, 𝐶 2 ⁢𝑆 exp are identical within statistical uncertainties. An explanation for the difference in 𝐶 2 ⁢𝑆 exp could be the removal of both halo protons, a more important reaction pathway for the C target. The 𝐶 2 ⁢𝑆 exp values obtained by analyzing the proton ejection from the core indicate that it is not affected by the interaction with the halo protons.

6 ≤ A ≤ 19↗
DOE OSTI2024

β -decay feeding intensity distribution of Mn 64

Nuclei around the N=40 “Island of Inversion” exhibit interesting structure features that have been the focus of several experimental and theoretical studies. Here, the present work presents the first complete study of the β-decay feeding intensity distribution and Gamow-Teller distribution for the β decay of 64 Mn to 64 Fe up to ~10 MeV. The β-decay intensity function was extracted from Total Absorption Spectroscopy measurements made at the National Superconducting Cyclotron Laboratory with the Summing NaI(Tl) (SuN) detector. The experimental results are compared to shell model calculations with and without the inclusion of the νg 9/2 orbital. From this comparison it is clear that the νg 9/2 orbital is essential for the accurate description of the 64 Fe β-decay strength above ~3 MeV, emphasizing once again the transitional nature of this nucleus into the N=40 Island of Inversion.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

High-precision mass measurement of Si 24 and a refined determination of the r p process at the A = 22 waiting point

We report a high-precision mass measurement of 24 Si, performed with the Low Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory. The atomic mass excess, 10 753.8 (37) keV, is a factor of 5 more precise than previous results. This substantially reduces the uncertainty of the 23 Al(p ,γ) 24 Si reaction rate, which is a key part of the rapid proton capture (rp) process powering type I x-ray bursts. Furthermore, the updated rate constrains the onset temperature of the (α,p) process at the 22 Mg waiting point to a precision of 9%.

20 ≤ A ≤ 38↗
DOE OSTI2022

In-beam γ-ray spectroscopy of 32 Mg via direct reactions

Background: The nucleus 32 Mg (N=20 and Z=12) plays a central role in the so-called “island of inversion,” where in the ground states sd-shell neutrons are promoted to the fp-shell orbitals across the shell gap, resulting in the disappearance of the canonical neutron magic number N=20. Purpose: The primary goals of this work are to extend the level scheme of 32Mg, provide spin-parity assignments to excited states, and discuss the microscopic structure of each state through comparisons with theoretical calculations. Method: In-beam γ-ray spectroscopy of 32 Mg was performed using two direct-reaction probes: one-neutron (two-proton) knockout reactions on 33 Mg ( 34 Si). Final-state exclusive cross sections and parallel momentum distributions were extracted from the experimental data and compared with eikonal-based reaction model calculations combined with shell-model overlap functions. Results: Owing to the remarkable selectivity of the one-neutron and two-proton knockout reactions, a significantly updated level scheme for 32 Mg, which exhibits negative-parity intruder and positive-parity normal states, was constructed. The experimental results were confronted with four different nuclear structure models. Conclusions: In some of these models, different aspects of 32 Mg and the transition into the island of inversion are well described. However, unexplained discrepancies remain, and, even with the help of these state-of-the-art theoretical approaches, the structure of this key nucleus is not yet fully captured.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Improved nuclear physics near A = 61 refines urca neutrino luminosities in accreted neutron star crusts

We performed Penning trap mass measurements for 61 Zn at the National Superconducting Cyclotron Laboratory and NuShellX calculations of the 61 Zn and 62 Ga structure using the GXPF1A Hamiltonian to obtain improved estimates of the 61 Zn(p,γ) 62 Ga and 60 Cu(p,γ) 61 Zn reaction rates. Surveying astrophysical conditions for type-I x-ray bursts with the code mesa, implementing our improved reaction rates, and taking into account updated nuclear masses for 61 V and 61 Cr from the recent literature, we refine the neutrino luminosity from the important mass number A = 61 urca cooling source in accreted neutron-star crusts. Furthermore, this improves our understanding of the thermal barrier between deep heating in the crust and the shallow depths where extra heat is needed to explain x-ray superbursts, as well as the expected signature of crust urca neutrino emission in light curves of cooling transients

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Unveiling the two-proton halo character of 17 Ne: Exclusive measurement of quasi-free proton-knockout reactions

The proton drip-line nucleus 17 Ne is investigated experimentally in order to determine its two-proton halo character. A fully exclusive measurement of the 17 Ne (p, 2p) 16 F* 15 O+p quasi-free one-proton knockout reaction has been performed at GSI at around 500 MeV/nucleon beam energy. All particles resulting from the scattering process have been detected. The relevant reconstructed quantities are the angles of the two protons scattered in quasi-elastic kinematics, the decay of 16 F into 15 O (including γ decays from excited states) and a proton, as well as the 15 O+p relative-energy spectrum and the 16 F momentum distributions. The latter two quantities allow an independent and consistent determination of the fractions of l = 0 and l = 2 motion of the valence protons in 17 Ne. With a resulting relatively small l = 0 component of only around 35(3)%, it is concluded that 17 Ne exhibits a rather modest halo character only. The quantitative agreement of the two values deduced from the energy spectrum and the momentum distributions supports the theoretical treatment of the calculation of momentum distributions after quasi-free knockout reactions at high energies by taking into account distortions based on the Glauber theory. Moreover, the experimental data allow the separation of valence-proton knockout and knockout from the 15O core. The latter process contributes with 11.8(3.1) mb around 40% to the total proton-knockout cross section of 30.3(2.3) mb, which explains previously reported contradicting conclusions derived from inclusive cross sections.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

The status and future of direct nuclear reaction measurements for stellar burning

The study of stellar burning began just over 100 years ago. Nonetheless, we do not yet have a detailed picture of the nucleosynthesis within stars and how nucleosynthesis impacts stellar structure and the remnants of stellar evolution. Achieving this understanding will require precise direct measurements of the nuclear reactions involved. Furthermore, this report summarizes the status of direct measurements for stellar burning, focusing on developments of the last couple of decades, and offering a prospectus of near-future developments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Coexisting normal and intruder configurations in 32 Mg

Situated in the so-called “island of inversion,” the nucleus 32 Mg is considered as an archetypal example of the disappearance of magicity at N = 20. We report on high statistics in-beam spectroscopy of 32 Mg with a unique approach, in that two direct reaction probes with different sensitivities to the underlying nuclear structure are employed at the same time. More specifically, states in 32 Mg were populated by knockout reactions starting from 33 Mg and 34 Si, lying inside and outside the island of inversion, respectively. The momentum distributions of the reaction residues and the cross sections leading to the individual final states were confronted with eikonal-based reaction calculations, yielding a significantly updated level scheme for 32 Mg and spin-parity assignments. By fully exploiting observables obtained in this measurement, a variety of structures coexisting in 32 Mg was unraveled. Comparisons with theoretical predictions based on shell-model overlaps allowed for clear discrimination between different structural models, revealing that the complete theoretical description of this key nucleus is yet to be achieved.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Quenching of single-particle strengths in direct reactions

A discrepancy in the asymmetry dependence of spectroscopic factors extracted with different reaction probes calls into question whether the corresponding reaction models are properly understood. In this work, we present extracted spectroscopic factors from the Ar 46 , 34 ( p , d ) Ar 45 , 33 transfer reactions in inverse kinematics at a beam energy of 70 MeV/nucleon. The results are consistent with previous measurements of these reactions at a lower beam energy [Lee et al. , Phys. Rev. Lett. 104 , 112701 (2010) ], indicating that the transfer reaction is a reliable probe for the nuclear structure of exotic nuclei across a wide energy range. Results from a large body of transfer reaction measurements, ( p , p N ) measurements, and theoretical nuclear structure studies make a compelling case for much weaker asymmetry dependence than what is observed with single-nucleon knockout reactions on beryllium or carbon targets.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

β Decay of 61 V and its Role in Cooling Accreted Neutron Star Crusts

The interpretation of observations of cooling neutron star crusts in quasipersistent x-ray transients is affected by predictions of the strength of neutrino cooling via crust Urca processes. The strength of crust Urca neutrino cooling depends sensitively on the electron-capture and β -decay ground-state-to-ground-state transition strengths of neutron-rich rare isotopes. Nuclei with a mass number of A = 61 are predicted to be among the most abundant in accreted crusts, and the last remaining experimentally undetermined ground-state-to-ground-state transition strength was the β decay of 61 V. This Letter reports the first experimental determination of this transition strength, a ground-state branching of $8.1^{+4.0}_{- 3.1}%$, corresponding to a log ft value of $5.5^{+0.2}_{-0.2}$. This result was achieved through the measurement of the β -delayed γ rays using the total absorption spectrometer SuN and the measurement of the β -delayed neutron branch using the neutron long counter system NERO at the National Superconducting Cyclotron Laboratory at Michigan State University. This method helps to mitigate the impact of the pandemonium effect in extremely neutron-rich nuclei on experimental results. The result implies that A = 61 nuclei do not provide the strongest cooling in accreted neutron star crusts as expected by some predictions, but that their cooling is still larger compared to most other mass numbers. Finally, only nuclei with mass numbers 31, 33, and 55 are predicted to be cooling more strongly. However, the theoretical predictions for the transition strengths of these nuclei are not consistently accurate enough to draw conclusions on crust cooling. With the experimental approach developed in this work, all relevant transitions are within reach to be studied in the future.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Structure of 30 Mg explored via in-beam γ-ray spectroscopy

In the island of inversion, ground states of neutron-rich sd-shell nuclei exhibit strong admixtures of intruder configurations from the fp shell. The nucleus 30 Mg, located at the boundary of the island of inversion, serves as a cornerstone to track the structural evolution as one approaches this region. Spin-parity assignments for excited states in 30 Mg, especially negative-parity levels, have yet to be established. In the present work, the nuclear structure of 30Mg was investigated by in-beam gamma-ray spectroscopy mainly focusing on firm spin-parity determinations. High-intensity rare-isotope beams of 31 Mg, 32 Mg, 34 Si, and 35 P bombarded a Be target to induce nucleon removal reactions populating states in 30 Mg. Gamma rays were detected by the state-of-the-art gamma-ray tracking array GRETINA. For the direct one-neutron removal reaction, final-state exclusive cross sections and parallel momentum distributions were deduced. Multi-nucleon removal reactions from different projectiles were exploited to gain complementary information. With the aid of the parallel momentum distributions, an updated level scheme with revised spin-parity assignments was constructed. Spectroscopic factors associated with each state were also deduced. Results were confronted with large-scale shell-model calculations using two different effective interactions, showing excellent agreement with the present level scheme. Furthermore, a marked difference in the spectroscopic factors indicates that the full delineation of the transition into the island of inversion remains a challenge for theoretical models.

20 ≤ A ≤ 38↗
DOE OSTI2020

Nuclear mass measurements map the structure of atomic nuclei and accreting neutron stars

We introduce here mass excesses (ME) of neutron-rich isotopes of Ar through Fe, obtained via time of flight B ρ mass spectrometry at the National Superconducting Cyclotron Laboratory. Our new results have significantly reduced systematic uncertainties relative to a prior analysis, enabling the first determination of ME for Ti 58 , 59 , V 62 , Cr 65 , Mn 67 , 68 , and Fe 69 , 70 . Our results show the N = 34 subshell weaken at Sc and vanish at Ti, along with the absence of an N = 40 subshell at Mn. This further leads to a cooler accreted neutron star crust, highlighting the connection between the structure of nuclei and neutron stars.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗