H.H. Bolotin

Lifetimes of excited states in 196, 198Pt; Application of interacting boson approximation model to even Pt isotopes systematics

Abstract The lifetimes and lifetime limits of the low-lying excited states up to and including the 6 1 + levels in 196, 198 Pt were determined by the recoil-distance method (RDM). Gamma-ray angular distributions in 198 Pt were also measured. These states were populated by multiple Coulomb excitation using 220 MeV 58 Ni ion beams and the measurements were carried out in coincidence with back-scattered projectiles. The measured mean lives of the states and B (E2) values inferred for the transitions between levels are presented. These specific findings, and the observed structure systematics obtained from the combination of the present results and those of prior workers for the even 194–198 Pt isotopes, are critically compared with our structure calculations employing the interacting boson approximation (IBA) model incorporating a symmetry-breaking quadrupole force; evaluative comparisons are also made with boson expansion theory (BET) calculations.

Critical assessment of interacting boson model wave functions from measured gyromagnetic ratios of lowest eigenstates in even Os isotopes

Abstract The gyromagnetic ratios of the low-lying levels in the even 188−192 Os isotopes were measured. Of particular import, the ratios g (2 + 2 )/ g (2 + 1 ) were found to be 1.45 ± 0.18, 0.99 ± 0.14, and 0.72 ± 0.06 in 188 Os, 190 Os, and 192 Os, respectively. Although the E2 observables in these nuclides are accommodated quite well in interacting boson model descriptions (IBM-1 and IBM-2), both formulations fail to concurrently account for either the intra-nucleus or mass-dependent g -factor variations of the lowest eigenstates in these Os isotopes.

Gyromagnetic ratios of excited states in 198Pt; measurements and interacting boson approximation model calculations

Abstract The enhanced transient hyperfine field manifest at the nuclei of swiftly recoiling ions traversing magnetized ferromagnetic materials was utilized to measure the gyromagnetic ratios of the 2 + 1 , 2 + 2 and 4 + 1 states in 198 Pt by the thin-foil technique. The states of interest were populated by Coulomb excitation using a beam of 220 MeV 58 Ni ions. The results obtained were: g (2 + 1 ) = 0.324 ± 0.026; g (2 + 2 ) = 0.34 ± 0.06; g (4 + 1 ) = 0.34 ± 0.06. In addition, these measurements served to discriminate between the otherwise essentially equally probable values previously reported for the E2/M1 ratio of the 2 + 2 → 2 + 1 transition in 198 Pt. We also performed interacting boson approximation (IBA) model-based calculations in the O(6) limit symmetry, with and without inclusion of a small degree of symmetry breaking, and employed the M1 operator in both first- and second-order to obtain M1 selection rules and to calculate gyromagnetic ratios of levels. When O(6) symmetry is broken, there is a predicted departure from constancy of the g -factors which provides a good test of the nuclear wave function. Evaluative comparisons are made between these experimental and predicted g -factors.

The 2046 keV 27Al(p,γ)28Si resonance-capture reacion as a gamma-ray intensity calibration standard

Abstract The relative intensities and angular distributions of the prominent gamma rays following 27 Al(p,γ) 28 Si resonance capture at an incident proton energy of (2046.2±0.2) keV have been measured with a view to assessing the aptness and applicability of this resonance as a new, convinient secondary gamma-ray calibration standard for Ge(Li) detection efficiency determinations. These γ-ray transitions, which span the energy range from ∼1.8 to ∼9 MeV relatively uniformly, have been carefully studied. Detailed properties of the resonant state including the strength of its decay modes and its width have been determined. A possible spin assignment of 4 + is suggested for this resonant state.

Gyromagnetic ratios of excited states in 150Sm and 152Sm

Abstract The gyromagnetic ratios of the 2 1 + , 4 1 + , 6 1 + , 2 2 + , and 2 3 + states in 150 Sm and the 2 1 + , 4 1 + , 6 1 + , 8 1 + , 10 1 + , 2 2 + , and 2 3 + levels in 152 Sm have been measured using the transient field perturbed γ-ray angular correlation technique. States of interest were populated by multiple Coulomb excitation using 150- and 220-MeV 58 Ni beams. The present results display no significant deviation from constancy of the g -factors of all levels investigated in either isotope separately or of corresponding states in 150,152 Sm. These findings are compared with available prior measurements and assessed in terms of applicable theoretical model calculations.

Transient field measurements of g-factors in 194,196,198Pt; g(21+) systematics in transitional W, Os, Pt nuclei

Abstract Transient field precessions were measured simultaneously for levels in the nuclei 182,184,186 W and 1942,196,198 Pt as their ions traversed polarized Gd hosts. These results allow a critical evaluation of conflicting g -factor values reported previously for the even Pt isotopes. Mass variations of g (2 1 + ) in the even W, Os, Pt nuclei are examined using the proton-neutron interacting boson model (IBM-2). The measured g -factors depart from the simplest IBM-2 description perhaps due to Subshell effects and/or small contributions from non-collective configurations which cause the neutron boson g -factor to vary with mass.

Disparity of measured gyromagnetic ratios of ground- and excited-band states in184W

Gyromagnetic ratios of levels in the ground-band and of the 22+ state in184W were measured by means of the transient magnetic field perturbedγ-ray angular distribution technique. The levels of interest were Coulomb excited by beams of 220-MeV58Ni and63Cu ions. The results show theg-factor of the 22+ state to be approximately half the effectively constant value found for the ground-band levels. This disparity is compared with those previously obtained for the corresponding states in188–192Os and186W; these are discussed in the context of the interacting boson model.

Tests of interacting boson model wave functions from measured gyromagnetic ratios of states in the even Os isotopes

Abstract The gyromagnetic ratios of the 2 1 + , 2 2 + , and 4 1 + states in 188,190,192 Os were experimentally measured. It is shown that the hamiltonians of standard interacting boson models (IBM-1 and -2) fit to level spectra and B (E2) rates fail to account for either the intra-nucleus or mass-dependent g -factor variations of these states in these Os isotopes.

Gyromagnetic ratios of excited states in186W

The gyromagnetic ratios of the 41+, 61+, and 22+ states in186W were measured relative to that of the 21+ level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV63Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(41+)/g(21+)=1.04±0.07,g(61+)/g(21+)=1.03 ±0.20 andg(22+)/g(21+)=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.

The low excitation spectroscopy of 56, 57, 58Fe

Abstract The lifetimes of 21 states in 58Fe up to an excitation energy of 4213 keV have been determined by means of the Doppler-shift attenuation method using the 55Mn(α, pγ) reaction. These results complement other experimental data in an analysis of the structures of the 56 57 58Fe nuclides. A shell-model study has also been carried out in which the protons are constrained to the f 7 2 shell while valence neutrons are restricted to the f 5 2 - p 3 2 - p 1 2 subgroup. Good agreement with most low excitation data is found, as well as with the triaxial rotor models for these nuclides.