Search NASA⌕ Search

Engineering topics

Schatz, H.

Publications and source records attributed to Schatz, H..

14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Enhanced production of 60 Fe in massive stars

Massive stars are a major source of chemical elements in the cosmos, ejecting freshly produced nuclei through winds and core-collapse supernova explosions into the interstellar medium. Among the material ejected, long-lived radioisotopes, such as 60 Fe (iron) and 26 Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed 60 Fe/ 26 Al ratio by γ-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing 60 Fe, and one reaction in particular, the neutron-capture on 59 Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of 60 Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted 60 Fe/ 26 Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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

Proton Shell Gaps in N = 28 Nuclei from the First Complete Spectroscopy Study with FRIB Decay Station Initiator

The first complete measurement of the $β$-decay strength distribution of $_{17}^{45}$Cl 28 was performed at the Facility for Rare Isotope Beams (FRIB) with the FRIB Decay Station Initiator during the second FRIB experiment. The measurement involved the detection of neutrons and $γ$ rays in two focal planes of the FRIB Decay Station Initiator in a single experiment for the first time. This enabled an analytical consistency in extracting the $β$-decay strength distribution over the large range of excitation energies, including neutron unbound states. Here, we observe a rapid increase in the $β$-decay strength distribution above the neutron separation energy in $_{18}^{45}$Ar 27 . This was interpreted to be caused by the transitioning of neutrons into protons excited across the Z = 20 shell gap. The SDPF-MU interaction with reduced shell gap best reproduced the data. The measurement demonstrates a new approach that is sensitive to the proton shell gap in neutron rich nuclei according to SDPF-MU calculations.

39 ≤ A ≤ 58↗
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 OSTI2024

Mass measurements of neutron-rich nuclei near $N = 70$

The astrophysical origin for the chemical elements between the first and second r-process peaks is a matter of intense debate, with a number of nucleosynthesis processes at explosive stellar environments possibly contributing to their production. Reliable data on the trends of neutron separation energies of neutron-rich isotopes are required to model neutron-capture processes that would produce these elements. Masses of 104 Y, 106 Zr, 112 Mo, and 115 Tc have been measured with the time-of-flight-magnetic-rigidity (ToF–Bρ) technique at the National Superconducting Cyclotron Laboratory at Michigan State University. The experiment is the first application of the ToF–Bρ technique at the S800 spectrograph that reached the mass region relevant to heavy-element nucleosynthesis. Finally, the two-neutron separation energy deduced from the measured masses exhibits a smooth trend consistent with the theoretical predictions within the range of experimental uncertainty, indicating that there is no sudden shape transition in these isotopes as hinted at by previous data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

First Direct Measurement Constraining the Ar 34 ( α , p ) K 37 Reaction Cross Section for Mixed Hydrogen and Helium Burning in Accreting Neutron Stars

The rate of the final step in the astrophysical αp process, the 34 Ar(α,p) 37 K reaction, suffers from large uncertainties due to a lack of experimental data, despite having a considerable impact on the observable light curves of x-ray bursts and the composition of the ashes of hydrogen and helium burning on accreting neutron stars. Here, we present the first direct measurement constraining the 34Ar(α,p)37K reaction cross section, using the Jet Experiments in Nuclear Structure and Astrophysics gas jet target. The combined cross section for the 34 Ar,Cl(α,p) 37 K,Ar reaction is found to agree well with Hauser-Feshbach predictions. The 34 Ar(α,2p) 36 Ar cross section, which can be exclusively attributed to the 34 Ar beam component, also agrees to within the typical uncertainties quoted for statistical models. This indicates the applicability of the statistical model for predicting astrophysical (α,p) reaction rates in this part of the αp process, in contrast to earlier findings from indirect reaction studies indicating orders-of-magnitude discrepancies. This removes a significant uncertainty in models of hydrogen and helium burning on accreting neutron stars.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Horizons: nuclear astrophysics in the 2020s and beyond

Nuclear astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Establishing the ground-state spin of 71 Kr

Nuclei in the vicinity of the N=Z line provide many sensitive probes of isospin symmetry. One example concerns the character and sequence of low-lying states of the T=1/2 mirror pair 71 Kr and 71 Br which has been under debate for several decades. In this paper we report a new measurement of the absolute β-branching to ground and excited states which, taken with our precise lifetime of T 1/2 =94.9(4) ms , gives a superallowed ground state–to–ground state log (ft) value of 3.64(4). This is only consistent with both 71 Br and 71 Kr having the same spin and parity, J π =5/2 – , as expected from mirror symmetry. The β-delayed proton emission to the first-excited state in 70 Se was observed for the first time which also strongly supports this assignment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

57 Zn β-delayed proton emission establishes the 56 Ni rp-process waiting point bypass

We measured the 57 Zn β-delayed proton (βp) and γemission at the National Superconducting Cyclotron Laboratory. We find a 57 Zn half-life of 43.6 ± 0.2ms, βp branching ratio of (84.7 ±1.4)%, and identify four transitions corresponding to the exotic β-γ-pdecay mode, the second such identification in the fp-shell. The p/γratio was used to correct for isospin mixing while determining the 57 Zn mass via the isobaric multiplet mass equation. Previously, it was uncertain as to whether the rp-process flow could bypass the textbook waiting point 56 Ni for astrophysical conditions relevant to Type-I X-ray bursts. Our results definitively establish the existence of the 56 Ni bypass, with 14-17% of the rp-process flow taking this route.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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 OSTI2021

Mass measurements of 60–63 Ga reduce x-ray burst model uncertainties and extend the evaluated T=1 isobaric multiplet mass equation

We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of 60–63 Ga performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of 61 Ga and mark the first direct mass measurement of 60 Ga. The improved precision of the 61 Ga mass has important implications for the astrophysical rp process, as it constrains essential reaction Q values near the 60 Zn waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of x-ray burst models. The first-time measurement of the 60 Ga ground-state mass establishes the proton-bound nature of this nuclide, thus constraining the location of the proton drip line along this isotopic chain. Including the measured mass of 60 Ga further enables us to extend the evaluated T = 1 isobaric multiplet mass equation up to A = 60.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗