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Smith, J. F.

Publications and source records attributed to Smith, J. F..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Decay of a microsecond seniority 3 isomeric state in Hf 155

Excited states in the neutron-deficient nuclide Hf 155 have been investigated in experiments performed at the Accelerator Laboratory of the University of Jyväskylä. The Hf 155 nuclei were produced in fusion-evaporation reactions induced by beams of 295 and 315 MeV Ni 58 ions bombarding an isotopically enriched Pd 102 target and separated using the recoil mass separator MARA. An isomeric state having a half-life of 510(30) ns was discovered and is interpreted as a seniority υ = 3 , ( π h 11 / 2 2 ⊗ ν f 7 / 2 ) 27 / 2 − configuration. The γ -ray transitions emitted in the deexcitation of the isomeric state to the ground state were identified and a level scheme was constructed, from which the excitation energy of the isomer was determined to be 2581.5(10) keV. A B ( E 2 ) value of 0.45(3) W.u. was deduced for the 105.4 keV transition depopulating the isomeric state. The deduced level scheme and B ( E 2 ) value are compared with systematics and shell-model calculations. Published by the American Physical Society 2024

Physics↗
DOE OSTI2023

Decay spectroscopy at the two-proton drip line: Radioactivity of the new nuclides 160 Os and 156 W

The radioactivity of $^{160}_{76}$Os 84 and $^{156}_{74}$W 82 that lie at the two-proton drip line has been measured in an experiment performed at the Accelerator Laboratory of the University of Jyväskylä. The 160 Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV 58 Ni ions bombarding a 106 Cd target. The 160 Os ions were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. The α decays of the ground state of 160 Os (Ε α = 7092(15) keV, t 1/2 = 97$^{+97}_{-32}$ μs) and its isomeric state (Ε α = 8890(10) keV, t 1/2 = 41$^{+15}_{-9}$ μs) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These α-decay properties and the excitation energy of the isomer are compared with systematics. The α decays were correlated with subsequent decays to investigate the β decays of the ground state of 156 W, revealing that unlike its isotones, both low-lying isomers were populated in its daughter nuclide, 156 Ta. An improved value for the half-life of the proton-decaying high-spin isomeric state in $^{156}_{73}$Ta 83 of 333$^{+25}_{-22}$ ms was obtained in a separate experiment using the same experimental systems with a 102 Pd target. This result was employed to improve the precision of the half-life determined for 156 W, which was measured as 157$^{+57}_{-34}$ ms.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Photo-response of the $N=Z$ nucleus $^{24}$Mg

The electric E1 and magnetic M1 dipole responses of the N = Z nucleus 24 Mg were investigated in an inelastic photon scattering experiment. The 13.0 MeV electrons, which were used to produce the unpolarised bremsstrahlung in the entrance channel of the 24 Mg(γ,γ') reaction, were delivered by the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The collimated bremsstrahlung photons excited one J π = 1 – , four J π = 1 + , and six J π = 2 + states in 24 Mg. De-excitation γ rays were detected using the four high-purity germanium detectors of the γELBE setup, which is dedicated to nuclear resonance fluorescence experiments. In the energy region up to 13.0 MeV a total B(M1)↑ = 2.7(3) $μ$$^{2}_{N}$ is observed, but this N = Z nucleus exhibits only marginal E1 strength of less than ΣB(E1)↑≤ 0.61 × 10 –3 e 2 fm 2 . The B(Π1, $1$$^{π}_{i}$ → $2$$^{+}_{1}$)/B(Π1,$1$$^{π}_{i}$ → $0$$^{+}_{gs}$) branching ratios in combination with the expected results from the Alaga rules demonstrate that K is a good approximative quantum number for 24 Mg. The use of the known ρ 2 (E0, $0$$^{+}_{2}$ → $0$$^{+}_{gs}$) strength and the measured B(M1,1 + → $0$$^{+}_{2}$)/B(M1,1 + → $0$$^{+}_{gs}$) branching ratio of the 10.712 MeV 1 + level allows, in a two-state mixing model, an extraction of the difference Δ$β$$^{2}_{2}$ between the prolate ground-state structure and shape-coexisting superdeformed structure built upon the 6432-keV $0$$^{+}_{2}$ level.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Lifetime measurements of states of S 35 , S 36 , S 37 , and S 38 using the AGATA γ -ray tracking spectrometer

Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers A = 35 , 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of 36 S ions of energy 225 MeV incident on a thin 208 Pb target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA γ-ray tracking array was used to detect γ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For 35 S, the lifetime was determined for the first 1/2 + state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the 3 - state of 36 S at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (6 + ) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For 37 S, the states for which lifetime limits were established were those at 646 keV with J π = 3/2 - and at 2776 keV with J π = 11/2 - ; there are no previously published lifetime values for excited states of 37 S. Finally, a lifetime limit was established for the J π =(6 + ) state of 38 S at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.

electromagnetic transitions↗
DOE OSTI2021

Sensitive search for near-symmetric and super-asymmetric fusion-fission of the superheavy element Flerovium (Z=114)

Measurements of mass and angular distributions have been made for fission-like outcomes in reactions forming isotopes of flerovium (Z=114), using 48 Ca, 50 Ti, and 54 Cr projectiles. The dominant fast quasifission process, which masks the presence of fusion-fission, has minimum yield at the most backward angles, where the sensitivity to fusion-fission is thus highest. In fitting the backward angle mass spectra, only weak evidence for a component of super-asymmetric fission was found, but a near-symmetric fission component was consistently required for the 48 Ca + 244 Pu reaction, giving upper limit to the fusion probabilities P CN of ~10 -2 , ~5 times lower than previous results. P CN for the 50 Ti reaction was lower than 48 Ca, whilst no evidence of fusion-fission was found for the 54 Cr reaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Consistency of nucleon-transfer sum rules in well-deformed nuclei

Here, nucleon-transfer sum rules have been assessed via a consistent reanalysis of cross-section data from neutron-adding (d, p) and -removing (d, t) reactions on well-deformed isotopes of Gd, Dy, Er, Yb, and W, with 92 ≤ N ≤ 108 , studied at the Niels Bohr Institute in the 1960s and 1970s. These are complemented by new measurements of cross sections using the (d, p), (d, t), and (p, d) reactions on a subset of these nuclei. The sum rules, defined in a Nilsson-model framework, are remarkably consistent. A single overall normalization is used in the analysis, which appears to be sensitive to assumptions about the reaction mechanism, and in the case of sums using the (d, t) reaction, differs from values determined from reactions on spherical systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes: Coulomb excitation of 182 Hg, 184 Hg, 186 Hg and 188 Hg

The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of 0 + 1,2 , 2 + 1,2 and 4 + 1 states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Low-lying octupole isovector excitation in Nd 144

The nature of low-lying 3 – levels in 144 Nd was investigated in the 143 Nd(n, γγ) cold neutron-capture reaction. The combination of the high neutron flux from the research reactor at the Institut Laue-Langevin and the high γ-ray detection efficiency of the EXILL setup allowed the recording of γγ coincidences. From the coincidence data precise branching ratios were extracted. Furthermore, the octagonal symmetry of the setup allowed angular-distribution measurements to determine multipole-mixing ratios. Additionally, in a second measurement the ultra-high resolution spectrometer GAMS6 was employed to conduct lifetime measurements using the gamma-ray induced Doppler-shift technique (GRID). The confirmed strong M1 component in the 3 – 3 → 3 – 1 decay strongly supports the assignment of the 3 – 3 level at 2779 keV as low-lying isovector octupole excitation. Here, the microscopic calculations within the quasiparticle phonon model confirm an isovector component in the wave function of the 3 – 3 level, firmly establishing this fundamental mode of nuclear excitation in near-spherical nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Parity-Doublet Structure in the $147\atop{57}$La 90 nucleus

Excited states in 147 La, populated in spontaneous fission of 252 Cf have been reinvestigated by means of γ spectroscopy, using high-fold γ coincidences measured with Gammasphere array of Ge detectors. The 229.5-keV level, which has been assigned spin-parity 9/2 - in a recent evaluation, is shown to have spin-parity 11/2 - . Consequently, the ground state has spin-parity 5/2 + . Excited levels in 147 La have been arranged into a parity-doublet structure, showing that at medium excitation energy the 147 La nucleus may have octupole deformation. In conclusion, the B ( E 1) rates in 147 La, which are factor four lower than in 145 La, suggest that the electric dipole moment in 147 La is depresses by an extra mechanism, probably connected with the population of particular neutron orbitals.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

High-spin structures in Xe 132 and Xe 133 and evidence for isomers along the N = 79 isotones

In this study, the transitional nuclei 132 Xe and 133 Xe are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in 136 Xe + 208 Pb MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the 136 Xe + 198 Pt MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a 130 Te (α,xn) 134-xn Xe fusion-evaporation reaction employing the HORUS γ -ray array at the University of Cologne. The high-spin level schemes are considerably extended above the J π = (7 - ) and (10 + ) isomers in 132 Xe and above the 11/2 - isomer in 133 Xe. The results are compared to the high-spin systematics of the Z = 54 as well as the N = 78 and N = 79 chains. Furthermore, evidence is found for a long-lived (T 1/ 2 » 1 μs) isomer in 133 Xe which closes a gap along the N = 79 isotones. Finally, shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

New excitations in Ba 142 and Ce 144 : Evolution of γ bands in the N = 86 isotones

New excited states in 142 Ba and 144 Ce are investigated by means of prompt γ-ray spectroscopy of the radiation following spontaneous fission of 252 Cf. Measurements of angular correlations and the observed branchings allowed the assignment of spins and parities with confidence. The new measurements are reinforced by shell-model calculations where energy levels, electric transitions, and magnetic moments are consistent with experimental data. Lastly, the presence of collectivity in the N = 86 isotones is confirmed by clear signatures of soft triaxial γ bands in both nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Isomers and high-spin structures in the N = 81 isotones Xe 135 and Ba 137

In this study, the high-spin structures and isomers of the N=81 isotones 135 Xe and 137 Ba are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in 136 Xe + 238 U and (ii) 136 Xe+ 208 Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the 136 Xe+ 198 Pt MNT reaction employing the γ-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a 11 B+ 130 Te fusion-evaporation reaction with the HORUS γ-ray array at the University of Cologne. The high-spin level schemesof 135 Xe and 137 Ba are considerably extended to higher energies. The 2058-keV (19/2 - ) state in 135 Xe is identified as an isomer, closing a gap in the systematics along the N=81 isotones. Its half-life is measured to be 9.0(9) ns, corresponding to a reduced transition probability of B(E2,19/2 - →15/2 - )=0.52(6) W.u. The experimentally deduced reduced transition probabilities of the isomeric states are compared to shell-model predictions. Finally, latest shell-model calculations reproduce the experimental findings generally well and provide guidance to the interpretation of the new levels.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Configurations and decay hindrances of high- K states in Hf 180

Multi-quasiparticle high-K states, several of which are isomeric, were observed in Hf-180 with the Gammasphere array. We determined the lifetimes in the ns-μs range using centroid-shift and decay measurements within a mu s coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to K π = (18 - ) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Furthermore, rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Rearrangement of valence neutrons in the neutrinoless double- β decay of Xe 136

Here, a quantitative description of the change in ground-state neutron occupancies between 136 Xe and 136 Ba, the initial and final state in the neutrinoless double-β decay of 136 Xe, has been extracted from precision measurements of the cross sections of single-neutron-adding and -removing reactions. Comparisons are made to recent theoretical calculations of the same properties using various nuclear-structure models. These are the same calculations used to determine the magnitude of the nuclear matrix elements for the process, which at present disagree with each other by factors of 2 or 3. The experimental neutron occupancies show some disagreement with the theoretical calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

High-spin structure of Xe 134

Detailed spectroscopic information on the N~82 nuclei is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in 134 Xe is investigated after multinucleon transfer (MNT) and actinide fission. Xenon-134 was populated as (i) a transfer product in 136 Xe+ 238 U and 136 Xe+ 208 Pb MNT reactions and (ii) as a fission product in the 136 Xe+ 238 U reaction employing the high-resolution Advanced Gamma Tracking Array (AGATA). Trajectory reconstruction has been applied for the complete identification of beamlike transfer products with the magnetic spectrometer PRISMA. The 136 Xe+ 198 Pt MNT reaction was studied with the γ-ray spectrometer GAMMASPHERE in combination with the gas detector array Compact Heavy Ion Counter (CHICO). Several high-spin states in 134 Xe on top of the two long-lived isomers are discovered based on γγ-coincidence relationships and information on the γ-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of 134 Xe is extended up to an excitation energy of 5.832 MeV with tentative spin-parity assignments up to 16 + . Previous assignments of states above the 7 - isomer are revised. Latest shell-model calculations employing two different effective interactions reproduce the experimental findings and support the new spin and parity assignments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗