J. K. Hwang

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.

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.

EVEN-PARITY BANDS OF 108, 110, 112Ru

High-spin, even-parity bands in neutron-rich 108, 110, 112Ru nuclei were reinvestigated and considerably expanded by measuring many-fold prompt γ-ray coincidence events following the spontaneous fission of 252Cf with Gammasphere. Our high statistics data allow us to detect weaker transitions and bands not previously published. Also, gamma branching ratios, which are important for theory, are carefully measured from all levels. In 110Ru, we find a doubling of levels for both ground and quasi-gamma bands above the 8+ levels. There are likely two-phonon quasi-gamma bands in 110, 112Ru, as well as a bandhead level in 108Ru. The odd–even spin energy band staggering observed in the quasi-gamma bands in 108, 110, 112Ru and the doubling of levels in 110Ru present a challenge to theory.

Binary and ternary fission studies with 252Cf

Abstract The spontaneous fission of 252 Cf has been studied via γ  γ  γ coincidences and γ  γ-light charged particle coincidences with Gammasphere. The yields of correlated Mo-Ba pairs in binary fission with 0–10 neutron emission have been remeasured with an uncompressed γγγ coincidence data. The previous hot fission mode with 8–10 neutron emission seen in the Mo-Ba split is found to be smaller than earlier results but still present. New 0n binary SF yields are reported. By gating on the light charged particles detected in ΔE-E Si detectors and γγ coincidences with Gammasphere, the relative yields of correlated pairs in alpha ternary fission with zero to 6n emission are observed for the first time. A number of correlated pairs are identified in ternary fission with 10 Be as the LCP. We observed only cold, 0n 10 Be and little, if any, hot, xn 10 Be channel.

Cold (Neutronless) Alpha Ternary Fission of 252Cf: Theory and Comparison with Experiment

A new phenomenon is studied: the cold (neutronless) ternary α-accompanied fragmentation of 252Cf. The corresponding isotopic yields were calculated as the ratio of the penetrability of a given fragmentation over the sum of penetrabilities of all possible (neutronless) α-ternary fragmentations. No preformation factors were considered. We considered that close to the scission configuration the nucleons of the alpha particle form a small neck. At a given value of the neck radius a double scission takes place and a third light fragment is formed between the two heavier fragments. The corresponding barriers between the light and heavy fragment and between the alpha particle and the two heavier fragments were evaluated by using a double folding potential generated by M3Y nucleon-nucleon forces and realistic fragment ground state deformations. The relative calculated isotopic yields greater than 2 × 10-3 have been observed experimentally for the partners with known spectra. We predict that fragmentations with unknown light partners 105,106Zr, 109,110Mo and 114Ru to be identified in the present data.

Identification of ν 9 / 2 [ 404 ] band in 97 Sr

An excited rotational band including seven new

Possible octupole correlation in {sup 147}Pr and {pi}h{sub 11/2} bands in {sup 149,151}Pr

\ensuremath{\gamma}

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

transitions was identified in

New data on the ternary fission of 252Cf from the Gammasphere facility

{}^{97}\mathrm{Sr}