B. R. S. Babu

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.

Octupole deformation in 142,143Ba and 144Ce: new band structures in neutron-rich Ba-isotopes

Abstract New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

The 108,110,112Ru isotopes in the generalized collective model

Abstract Very recently two groups reported on the measurement of excitation energies and γ-ray branching ratios for the very neutron-rich 108,110,112 Ru isotopes. The experimental data were analyzed using the rigid triaxial rotor and the rotation-vibration models resulting in basically different conclusions about the essential physics of these nuclei. In order to try to resolve this matter we applied the generalized collective model to these isotopes: Our results are compared systematically to the available experimental data and to calculations within the two aforementioned models.

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.

Identification of 152Ce and unexpected variations in moments of inertia with neutron number and spin in 142-148Ba, 144-152Ce and 146-156Nd

Levels in 152Ce are identified for the first time along with new high spin states in 142-148Ba, 144-150Ce and 150-156Nd from X-X, gamma -X and gamma - gamma - gamma -ray coincidence measurement in spontaneous fission of 252Cf and 242Pu. The N=88, 90 Ba nuclei have very nearly identical J1 for the yrast bands (2+ to 10+) and for the octupole bands (3- to 15-). The N=92, 94 Nd nuclei have essentially identical yrast J1 (0+ to 16+).

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.

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

Neutron-rich {sup 147,149,151}Pr nuclei, produced in the spontaneous fission of {sup 252}Cf, were studied using the Gammasphere array. Possible parity doublets in {sup 147}Pr with N=88 and {pi}h{sub 11/2} bands in {sup 149,151}Pr are proposed. These new data on the level structures of odd Pr isotopes suggest that octupole correlations may also be present in the neutron-rich {sub 59}{sup 147}Pr{sub 88} nucleus such as those observed in {sub 58}{sup 146}Ce{sub 88}, and also that the h{sub 11/2} bands in the {sup 149,151}Pr track in energy the yrast bands in {sup 148,150}Ce. The backbending related to the breaking of the neutron i{sub 13/2} pair is observed at {Dirac_h}{omega}{approx}0.27 (MeV) for the proton h{sub 11/2} band of {sup 149}Pr.

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.

Binary and ternary cold fission of252Cf

SummaryExperimental integral isotopic yields for the spontaneous cold (neutron-less) binary and α-ternary fission of252Cf were obtained by using triple γ-γ-γ coincidence technique at Gammasphere facility. For the first time10Be- and14C-ternary fission isotopic yields were also measured. The results are interpreted within simple cluster model with binary and ternary potential barriers generated by M3Y effective interaction and ground-state deformation.