K. Butler-Moore

New cold and ultra hot binary and cold ternary spontaneous fission modes for 252Cf and new band structures with gammasphere

Abstract Prompt γ-γ-γ and x-γ-γ coincidence studies following the spontaneous fission of 252Cf were carried out first at Oak Ridge then at Gammasphere first with 36 and later with 72 Ge and two x-ray detectors and a long x-ray-γ coincidence experiment at Idaho. Many new cases of correlated pairs in cold (zero neutron emission) binary fission are observed and for the first time the heavier correlated pairs are identified in ternary fission where the third partners are α, 6He (or α2n), 10Be and, tentatively, 14C. Theoretical calculations were carried out of the relative yields of cold binary and ternary fission. There is reasonable agreement between the relative theoretical and experimental yields. New level structures and isotopes include new octupole deformations, identical bands and other structures. Stable octupole deformation is now observed in N=86, 140Xe, 142Ba and 144Ba and 143Ba, 148Ba and to higher spin in 144Ba. The 142–146Ba data provide the first evidence for the predicted disappearance of stable octupole deformation at high spins from band crossings. Identical yrast bands are observed with widely different neutron and proton numbers in 98,100Sr, 108,110Ru, 112,116Pd, 144,146Ba, 152,154,156Nd, 156Sm, 160Gd and a new type of shifted identical bands in 156,158,160Sm as well as the first identical octupole bands in 142,144Ba. Other new level structures are found. Yields and neutron multiplicities were measured directly for SrNd, ZrCe, MoBa, RuXe, and PdTe correlated pairs. A new ultra hot fission mode was discovered going via only 108Mo144Ba, 107Mo145Ba, and/or 106Mo146Ba pairs where one or more of 44,145,146Ba are hyperdeformed at scission with 3:1 axis ratio.

New Spontaneous Fission Mode for 252Cf: Indication of Hyperdeformed 144,145,146Ba at Scission.

From {gamma}-ray coincidence studies following spontaneous fission of {sup 252}Cf, direct measurements of yields and neutron multiplicities were made for Sr-Nd, Zr-Ce, Mo-Ba, Ru-Xe, and Pd-Te correlated pairs. A strong enhancement of the 7-10 neutron channels for Mo-Ba pairs is observed. A new fission mode associated with the enhanced neutron yields is identified. These data can be interpreted in terms of one or more of {sup 144,145,146}Ba being hyperdeformed at scission. Mean field calculations predict a hyperdeformed third minimum in {sup 252}Cf and an extremely deformed {sup 146}Ba fragment at scission. {copyright} {ital 1996 The American Physical Society.}

Cold (neutronless)αternary fission of252Cf

The phenomenon of cold (neutronless) alpha ternary fission in spontaneous fission of {sup 252}Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Correlated pairs of {sub 36}Kr-{sub 60}Nd, {sub 38}Sr-{sub 58}Ce, {sub 40}Zr-{sub 56}Ba, {sub 42}Mo-{sub 54}Xe, {sub 44}Ru-{sub 52}Te, and {sub 46}Pd-{sub 50}Sn were observed to be associated with {alpha} ternary fission of {sup 252}Cf. Yields of cold {alpha} ternary fission were extracted. {copyright} {ital 1998} {ital The American Physical Society}

Observation of a vh{sub 11/2} pair alignment in neutron-rich {sup 118}Pd

The yrast band was significantly extended to 14{sup +} and the {gamma} band to 5{sup +} in neutron-rich {sup 118}Pd by measuring the {gamma}-{gamma}-{gamma} coincidences emitted from the spontaneous fission of {sup 252}Cf with Gammasphere. The first band crossing was observed in the yrast band in {sup 118}Pd at a frequency of {Dirac_h}{omega}{approx}0.36 MeV at the starting point of the backbending, which is similar to that found in {sup 112-116}Pd. The first bandbending in the yrast cascade in {sup 118}Pd is interpreted to be built on a two h{sub 11/2} neutron configuration based on its similarity to the yrast bands in even-even {sup 112-116}Pd. Our result indicates {sup 118}Pd still maintains a prolate shape. The quasineutron Routhian calculations indicate a lower crossing frequency for the h{sub 11/2} level.

High-spin states in neutron-rich even-even Pd isotopes

Transitions among high-spin states in 112,114,116Pd are observed through prompt -ray spectroscopy following the spontaneous fisson of 252Cf. Spins and parities are assigned to many newly observed levels based on angular correlation analysis and comparison with known spins and parities of less neutron-rich Pd nuclides. The -band structures are significantly extended. New rotational band structures are observed for the first time, and tentatively assigned negative parity. IBA-1 model calculations are performed for the ground state and -bands.

Cold binary and ternary fragmentations in spontaneous fission of252Cf

SummaryThe phenomenon of cold (neutronless) binary and ternary fission in spontaneous fission of252 Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Many correlated pairs for both binary and ternary (4He,10Be) fission were observed in the spontaneous fission of252 Cf. Yields of cold ternary and cold binary fission were extracted. These results are compared with the theoretical calculations using M3Y nucleon-nucleon potential and WKB approximation for barrier penetration.

Levels in 136Te and new high-spin states in neutron-rich N=84 isotones

Excited states have been identified for the first time in the neutron-rich nuclide 136Te by observing prompt gamma -rays from 252Cf spontaneous fission fragments. The technique of triple gamma -ray coincidences was used for the first time in a spontaneous fission study to identify 136Te. In addition, new high-spin states in N=84 138Xe (12+) and 140Ba (8+) and N=86 140Xe (10+) have been observed. These provide the first high-spin yrast band systematics for the N=84 isotones.

Identification of the

From an experiment with Gammasphere and a 252C spontaneous fission source, two bands with signatures -i and +i are identified in 153Nd Also several new transitions in 149Nd are observed for the first time. The band with signature -i in 153Nd shows no back bending, similar to the one observed in 161Er. The signature splitting observed in the ground band of 153Nd is similar to the ones observed in N=93 isotones in this mass region. In 149Nd the new transitions are placed into a band with a proposed configuration of .

\nu_{\frac 32}-[521]

The decay of {sup 96}Tc{sup g} has been studied using low-temperature nuclear orientation. Multipole mixing ratios have been deduced for several transitions in the daughter nucleus {sup 96}Mo by measuring {gamma}-ray anisotropies following the decay of the oriented {sup 96}Tc nuclei. These new mixing ratios are compared with those determined from previous measurements in light of the possible presence of a low-energy 6{sup +} mixed-symmetry state in {sup 96}Mo. {copyright} {ital 1999} {ital The American Physical Society}

Band in 153Nd and the γ-Transitions in 149Nd

The decay of {sup 96}Tc{sup g} has been studied using low-temperature nuclear orientation. Multipole mixing ratios have been deduced for several transitions in the daughter nucleus {sup 96}Mo by measuring {gamma}-ray anisotropies following the decay of the oriented {sup 96}Tc nuclei. These new mixing ratios are compared with those determined from previous measurements in light of the possible presence of a low-energy 6{sup +} mixed-symmetry state in {sup 96}Mo. {copyright} {ital 1999} {ital The American Physical Society}