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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Binding energies, charge radii, spins, and moments: Odd-odd Ag isotopes and discovery of a new isomer

We report on the masses and hyperfine structure of ground and isomeric states in 114,116,118,120 Ag isotopes, measured with the phase-imaging ion-cyclotron-resonance technique (PI-ICR) with the JYFLTRAP mass spectrometer and the collinear laser spectroscopy beamline at the Ion Guide Isotope Separator On-Line facility, Jyväskylä, Finland. We measured the masses and excitation energies, electromagnetic moments, and charge radii, and firmly established the nuclear spins of the long-lived states. A new isomer was discovered in 118 Ag and the half-lives of 118 Ag long-lived states were reevaluated. We unambiguously pinned down the level ordering of all long-lived states, placing the inversion of the 𝐼 = 0 − and 𝐼 = 4 + states at 𝐴 = 118 (𝑁 = 71). As a result, we compared the electromagnetic moments of each state to empirical single-particle moments to identify the dominant configuration where possible.

90 ≤ A ≤ 149↗
DOE OSTI2021

Persistence of the Z = 28 shell gap in A = 75 isobars: Identification of a possible ( 1 / 2 – ) μ s isomer in Co 75 and β decay to Ni 75

Here, the evolution of shell structure around doubly magic exotic nuclei is of great interest in nuclear physics and astrophysics. In the ‘southwest’ region of 78 Ni, the development of deformation might trigger a major shift in our understanding of explosive nucleosynthesis. To this end, new spectroscopic information on key close-lying nuclei is very valuable. We intend to measure the isomeric and β decay of 75 Co, with one-proton and two-neutron holes relative to 78Ni, to access new nuclear structure information in 75 Co and its β-decay daughters 75 Ni and 74 Ni. The nucleus 75 Co is produced in relativistic in-flight fission reactions of 238 U at the Radioactive Ion Beam Factory in the RIKEN Nishina Center. Its isomeric and β decay are studied exploiting the BigRIPS and EURICA setups. We obtain partial β-decay spectra for 75 Ni and 74 Ni, and report a new isomeric transition in 75 Co. The energy [E γ = 1914(2)keV] and half-life [t 1/2 = 13(6) μs] of the delayed γ ray lend support for the existence of a J π = (1/2 – ) isomeric state at 1914(2) keV. A comparison with PFSDG-U shell-model calculations provides a good account for the observed states in 75 Ni, but the first calculated 1/2 – level in 75 Co, a prolate K = 1/2 state, is predicted about 1 MeV below the observed (1/2 – ) level. The spherical-like structure of the lowest-lying excited states in 75 Ni is proved. In the case of 75 Co, the results suggest that the dominance of the spherical configurations over the deformed ones might be stronger than expected below 78 Ni. Further experimental efforts to discern the nature of the J π = (1/2 – ) isomer are necessary.

59 ≤ A ≤ 89↗
DOE OSTI2020

Nuclear Data Sheets for A=190

The evaluated experimental data are presented and evaluated for 15 known nuclides of mass 190 (Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po). This work supersedes earlier full evaluations of A=190 by 2003Si05, 1990Si09, 1982Le22 and 1973Sc42. For 190Hf, only the isotopic identification has been made, with no information about the half-life of the ground state or its decay properties. For 190 Ta, only one excited state as an isomer has been identified, but with no knowledge about its decay properties. For 190 W, 190 Re, 190 Bi and 190 Po, available spectroscopic data are scarce. Here, the decay schemes of 190 Ta, 190 W, 190 Au, 190 Hg, 190 Au isomer decay, 190 Tl (both the activities), 190 Pb, and 190 Bi (both the activities) are considered incomplete by the evaluators. At present, extensive level structures, both the low-spin and high-spin, are known for 190 Os, 190 Ir, 190 Pt, 190 Au, 190 Hg, 190 Tl and 190 Pb, but data for level lifetimes, and γ-ray transition probabilities are generally lacking.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Properties of 187 Ta Revealed through Isomeric Decay

Mass-separated 187 Ta114 in a high-spin isomeric state has been produced for the first time by multi-nucleon transfer reactions, employing an argon gas stopping cell and laser ionisation. Here, internal $γ$ rays revealed a $T$ 1/2 = 7.3±0.9 s isomer at 1778±1 keV, which decays through a rotational band with perturbations associated with the approach to a prolate-oblate shape transition. Model calculations show less influence from triaxiality compared to heavier elements in the same mass region. The isomer decay reduced $E$2 hindrance factor, $f$ $ν$ = 27±1, supports the interpretation that axial symmetry is approximately conserved.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Microsecond Isomer at the N = 20 Island of Shape Inversion Observed at FRIB

Excited-state spectroscopy from the first experiment at the Facility for Rare Isotope Beams (FRIB) is reported. A 24(2)-μs isomer was observed with the FRIB Decay Station initiator (FDSi) through a cascade of 224- and 401-keV γ rays in coincidence with 32 Na nuclei. This is the only known microsecond isomer (1 μs ≤T 1/2 <1 ms) in the region. This nucleus is at the heart of the N=20 island of shape inversion and is at the crossroads of the spherical shell-model, deformed shell-model, and ab initio theories. It can be represented as the coupling of a proton hole and neutron particle to 32 Mg, 32 Mg+π -1 +ν +1 . This odd-odd coupling and isomer formation provides a sensitive measure of the underlying shape degrees of freedom of 32 Mg, where the onset of spherical-to-deformed shape inversion begins with a low-lying deformed 2 + state at 885 keV and a low-lying shape-coexisting 0$^+_2$ state at 1058 keV. Here, we suggest two possible explanations for the 625-keV isomer in 32 Na: a 6 - spherical shape isomer that decays by E2 or a 0 + deformed spin isomer that decays by M2. The present results and calculations are most consistent with the latter, indicating that the low-lying states are dominated by deformation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Search for Weak Side Branches in the Electromagnetic Decay Paths of the 6526-keV 10 + Isomer in 54 Fe

High-spin nuclear isomers in $N≈Z$ nuclei between doubly magic 40 Ca and 56 Ni provide an excellent testing ground for the nuclear shell model and questions related to isospin symmetry breaking in the vicinity of the proton drip line. The purpose of the present study is to investigate the possibility of weak electromagnetic decay branches along the decay paths of the 6526-keV 10 + isomer in 54 Fe. The isomer was strongly populated by means of the fusion-evaporation reaction 24 Mg( 36 Ar,$α$2$p$) 54$m$ Fe. The Gammasphere array was used to detect $γ$-ray cascades emitted from the isomeric state. By means of $γγγ$ coincidences, weak non-yrast decay branches can be discriminated, with the isomer’s half-life confirmed at $T$ 1/2 = 363 (4) ns. The yrast ${6}_{1}^{+}$ → ${2}_{1}^{+}$ $E4$ cross-over transition was interrogated. The observations are compared with shell-model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Nuclear Data Sheets for A=212

Spectroscopic data for all nuclei with mass number A=212 have been evaluated and the corresponding level schemes from radioactive decay and reaction studies are presented. Highlights from this evaluation include the first observation of 212 Hg by 2010Al24 and the first measurement of the ground state half-life by 2012Be28and 2016Ca25. The first measurement of the β - decay of 212 Tl populating excited states in 2 12 Pb has been per-formed by 2014Mo02. Knowledge of excited levels and their half-lives in 212 Po has been significantly extended in the transfer reaction studies of 2010As01, 2010As03 and 2016Ko03, 2017Ko38. A new (9 - )isomer which α decays in 212 At was observed by 2007Ku30. The level scheme of 212 Rn was significantly extended through the(HI,xnγ) reaction studies of 2009Dr12 and 2008Dr01. New levels in 212 Ra were identified in a transfer reaction experiment by 2018Pa04. Finally, the α decay of both the ground state and an isomer in 216 U populating 212 Thwas reported for the first time by 2015Ma37 and 2015De22

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Measurements of Short-Lived Isomers from Photofission as a Method of Active Interrogation for Special Nuclear Materials

Isomeric fission products, such as 134m Te (T 1/2 = 164 ns) and 136m Xe (T 1/2 = 2.95 μs), are proposed as a signature of special nuclear materials in active interrogation applications. To test this conjecture, monoenergetic 9, 11, and 13 MeV photons from the HIγS facility are used to induce fission of 235 U, 238 U, and 239 Pu targets. The de-excitation γ rays of the isomers are measured using time-gated spectroscopy with high-purity germanium detectors. The 134m Te and 136m Xe isomers are detected and identified by the energy and decay half-life of their characteristic γ-ray transitions. The ratio of yields for these two signature γ rays, corresponding to 134m Te/( 136m Xe + 136 I), is found to be strongly correlated with the identity of the fissioning nuclei. These results show that fission-product isomers may be used in active interrogation to detect and identify special nuclear materials, even providing information on the isotopic enrichment. In conclusion, the feasibility of an active interrogation scenario using a bremsstrahlung beam is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

{beta}- and {gamma}-spectroscopy study of {sup 119}Pd and {sup 119}Ag

Neutron-rich Pd-119 nuclei were produced in fission of natural uranium, induced by 25-MeV protons. Fission fragments swiftly extracted with the Ion Guide Isotope Separation On-Line method were mass separated using a dipole magnet and a Penning trap, providing mono-isotopic samples of Pd-119. Their beta(-) decay was measured with gamma gamma- and beta gamma-spectroscopy methods using low-energy germanium detectors and a thin plastic scintillator. Two distinct nuclear-level structures were observed in Ag-119, based on the 1/2(-) and 7/2(+) isomers reported previously. The beta(-)decay work was complemented by a prompt-gamma study of levels in Ag-119 populated in spontaneous fission of (252)cf, performed using the Gammasphere array of germanium detectors. Contrary to previous suggestions, our data show that the 1/2(-) isomer is located below the 7/2(+) isomer and is proposed as a new ground state of Ag-119 with the 7/2(+) isomer excitation energy determined to be 33.4 keV. Our data indicate that there are two beta unstable isomers in Pd-119, a proposed ground state of Pd-119 with tentative spin 1/2(-) or 3/2(+) and a half-life of 0.88 s and the other one about 350 keV above, having spin (11/2(-)) and a half-life of 0.85 s. The higher-energy isomer probably decays to the 1/2(-) or 3/2(+) ground state via a gamma cascade comprising 18.7-219.8-X-keV transitions. The unobserved isomeric transition with energy X approximate to 100 keV probably has an E3 multipolarity. Its hindrance factor is significantly lower than for analogous E3 isomeric transitions in lighter Pd isotopes, suggesting an oblate deformation of levels in Pd-119. Oblate configurations in Ag-119 are discussed also.

Kurpeta, J↗
DOE OSTI2026

Transient hydroperoxyalkyl intermediates (•QOOH) in isopentane oxidation. II. Isomer-resolved unimolecular dynamics

Transient carbon-centered hydroperoxyalkyl intermediates (•QOOH) in isopentane oxidation are characterized by their time- and energy-resolved unimolecular dissociation dynamics to hydroxyl (OH) and cyclic ether products. Two distinct •QOOH isomers are examined with radical sites at a primary carbon of one of the methyl groups (β-Me) or a secondary carbon (β-Et) of the ethyl group. Energy-dependent unimolecular rates are obtained from the time-dependent appearance of OH products for the two isomers and compared with statistical microcanonical rates computed using RRKM theory, including heavy-atom tunneling, based on high-level theoretical calculations. A benchmark-corrected approach is utilized to compute high-accuracy stationary-point energies, most importantly, transition-state barriers, for the •QOOH_Me and •QOOH_Et isomers in isopentane oxidation, building on higher-level reference calculations for the oxidation of ethane (C 2 H 5 O 2 ) and propane (C 3 H 7 O 2 ), respectively. Here, the measured rates are compared with RRKM calculations incorporating the benchmark-corrected transition-state parameters, a vibrationally adiabatic multidimensional hindered-rotor treatment of key torsions, and quantum tunneling. Agreement between experiment and theory validates the statistical description and shows faster decay for •QOOH_Et due to its lower barrier. Both β-QOOH isomers decay almost exclusively to OH + cyclic ether products under the conditions studied.

Oxidation processes↗
DOE OSTI2026

Isomeric states in the neutron-rich 𝑁 = 108 nuclei 178 Yb and 179 Lu

A multinucleon transfer reaction with a 136 Xe beam and a gold-backed 176 Yb target populated isomers in N = 108 178 Yb and 179 Lu. The single decay from the t 1/2 = 203(16) ns isomer in 178 Yb to the I π = 4 + level in the ground-state band suggests a I π = 4 − assignment, and multiquasiparticle calculations associate this state with the K π = 4 − , ν 2 (1/2[510], 9/2[624]) configuration. At least two isomers were observed in 179 Lu. One likely couples the K π = 4 − configuration found in 178 Yb to the 9/2[514] quasiproton orbital to form a K π = 17/2 + level (t 1/2 = 1.0(4) µs) which primarily decays into the rotational band based on the 9/2[514] state. A second isomer was observed to decay into this same band, but at higher energy and spin. Based on its feeding pattern, its similarity to an isomer found in 181 Ta, and a multiquasiparticle calculation, it is proposed to correspond to a K π = 29/2 − state based on the π9/2[514]ν 2 (9/2[624], 11/2[615]) configuration. As a result, an analysis of the reduced hindrance factors for negative-parity, two-quasineutron isomers in the rare-earth region is presented as well.

150 ≤ A ≤ 189↗
DOE OSTI2025

Universal Effective Charges in the 𝑠⁢𝑑 and 𝑓⁡𝑝 Shells

The 247-keV state in 54 Sc, populated in the 𝛽 decay of 54 Ca, is reported here as a nanosecond isomer with a half-life of 26.0(22) ns. The state is interpreted as the 1 + member of the 𝜋⁢𝑓 7/2 ⊗ 𝜈⁢𝑓 5/2 spin-coupled multiplet, which decays to the 3 + ,𝜋⁢𝑓 7/2 ⊗ 𝜈⁢𝑝 1/2 ground state. The new half-life corresponds to a pure 𝐸⁢2 transition with a strength of 1.93(16) W.u., providing the most precise, unambiguous 𝐵⁡(𝐸⁢2) value in the neutron-rich 𝑓⁡𝑝 region to date for a nucleus with valence protons above 𝑍 = 20. Notably, it is roughly 4 times larger than the 𝐵⁡(𝐸⁢2;1/2 − → 5/2 − ) value in 55 Ca. The results, as compared to semiempirical and ab initio shell-model calculations, indicate (1) a weak 𝑁 = 34 subshell gap relative to 𝑁 = 32, (2) a large 𝐸⁢2 enhancement in Sc as compared to Ca due to 1⁢𝑝 − 1⁢ℎ proton excitations across 𝑍 = 28, and (3) empirical effective proton and neutron charges 𝑒 𝜋 = 1.30⁢(8)⁢𝑒 and 𝑒 𝜈 = 0.452⁢(7)⁢𝑒, respectively, that are in contrast to reports of 𝑒 𝜋 ≈1.1–1.15⁢𝑒 and 𝑒 𝜈 ≈ 0.6–0.8⁢𝑒 for 𝑓⁡𝑝-shell nuclei near 𝑁 = 𝑍. Here, we demonstrate that these reports are erroneous and that, in fact, a universal set of effective charges can be used across the 𝑠⁢𝑑 and 𝑓⁡𝑝 shells.

Beta decay↗
DOE OSTI2021

Astromers in the Radioactive Decay of r-process Nuclei

Certain nuclear isomers are well known to affect nucleosynthesis with important observable consequences (e.g., 26 Al and 180 Ta). We study the impact of nuclear isomers in the context of rapid neutron capture process (r-process) nucleosynthesis. Here we demonstrate that nuclear isomers are dynamically populated in the r process and that some are populated far from thermal equilibrium; this makes them astrophysical isomers, or "astromers." We compute thermally mediated transition rates between long-lived isomers and the corresponding ground states in neutron-rich nuclei. We calculate the temperature-dependent β-decay feeding factors, which represent the fraction of material going to each of the isomer and ground state daughter species from the β-decay parent species. We simulate nucleosynthesis following the decay of a solar-like r-process composition and include as separate species nuclear excited states with measured terrestrial half-lives greater than 100 μs. We introduce a new metric to identify those astromers most likely to be influential and summarize them in a table. Notable entries include many second peak nuclei (e.g., the Te isotopic chain) and previously overlooked isomers in stable nuclei (e.g., 119 Sn, 131 Xe, and 195 Pt). Finally, we comment on the capacity of isomer production to alter radioactive heating in an r-process environment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Identification of a new isomeric state in 76 Zn following the β decay of 76 Cu

Background: The evolution of nuclear shell structure far from stability can be explored by identifying and measuring the properties of isomers. Neutron-rich nuclei between the Z = 28 and Z = 50 closed shells have been the subject of recent studies which have identified a number of 0.1 - 10 µs isomers and measured detailed spectroscopic properties. Purpose: The purpose of this analysis was to identify and measure the properties of short-lived isomeric states populated following β decay in Z ≈ 30, N ≈ 50 nuclei near the doubly magic nucleus 78 Ni. Methods: Here, radioactive ions produced by beam fragmentation at the National Superconducting Cyclotron Laboratory were implanted into a CeBr 3 scintillator coupled to a pixelated photomultiplier tube. Ancillary arrays of HPGe clover and LaBr 3 detectors were positioned around the implantation detector to measure β-delayed γ rays. Results: The previously observed 2634-keV level in 76 Zn, populated following the β decay of 76 Cu, was identified as isomeric with a half-life of 25.4(4) ns. A combination of timing and γ-ray spectroscopy was used to confirm this assignment. Shell-model calculations were performed and indicate that this state may be a high-spin negativeparity state formed by the occupation of the ν0g 9/2 orbital. Conclusions: A new isomeric state in 76 Zn has been identified and its half-life was measured. Ambiguity about the structure of this state could be resolved with further experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗