L. A. Bernstein

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}

Yrast superdeformed band in 194 Pb: J π and E x

The yrast superdeformed band in {sup 194}Pb has been populated using the {sup 174}Yb({sup 25}Mg,5n){sup 194}Pb reaction at E{sub beam}=130 MeV. Decay {gamma} rays were detected using the GAMMASPHERE array at the 88-Inch Cyclotron. Twelve {gamma}-ray transitions have been observed directly linking three members of the {sup 194}Pb yrast superdeformed band to low-lying normal deformed levels. Anisotropy measurements indicate that these linking decays include E1, M1, and mixed M1/E2 multipolarities. The radiative widths deduced are very inhibited, typically B(E1){approximately}10{sup {minus}8} Weisskopf units (W.u.) and B(M1){approximately}10{sup {minus}5} W.u. Without recourse to {ital a priori} assumptions J{sup {pi}}=6{sup +} and E{sub x}=4878.4(3) keV have been unambiguously assigned to the lowest-lying observed superdeformed state (the state populated by the 170-keV intraband transition). The intensity of the observed primaries accounts for 21(2){percent} of the superdeformed band population. {copyright} {ital 1997} {ital The American Physical Society}

Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in (254)Rf

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the K^{π}=8^{-}, ν^{2}(7/2^{+}[624],9/2^{-}[734]) two-quasineutron and the K^{π}=16^{+}, 8^{-}ν^{2}(7/2^{+}[624],9/2^{-}[734])⊗8^{-}π^{2}(7/2^{-}[514],9/2^{+}[624]) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the ^{254}Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1) μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

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.

ONSET OF COLLECTIVITY IN NEUTRON-DEFICIENT PO-196,PO-198

We have studied via in-beam gamma-ray spectroscopy Po-196 and Po-198, which are the first neutron-deficient Po isotopes to exhibit a collective low-lying structure. The ratios of yrast state energi ...

{sup 92}Mo(n,xnypz{alpha}{gamma}) reactions for neutron energies up to 250 MeV

Excitation functions from the interaction of fast neutrons (up to an energy of 250 MeV) on a target of {sup 92}Mo have been measured. Yields have been determined for reaction {gamma} rays from {sup 88-92}Mo, {sup 88-92}Nb, {sup 86-91}Zr, {sup 84-86,88}Y, and {sup 80,82-86}Sr. These results are compared with model calculations using the GNASH code which takes into account compound nucleus, preequilibrium emission, multiple preequilibrium emission, and direct reaction contributions. The model calculations are in good agreement overall, but significant discrepancies emerge for some high-multiplicity, charged-particle-exit channels.

Low-energy enhancement in theγ-ray strength functions ofGe73,74

Author(s): Renstrom, T; Nyhus, HT; Utsunomiya, H; Schwengner, R; Goriely, S; Larsen, AC; Filipescu, DM; Gheorghe, I; Bernstein, LA; Bleuel, DL; Glodariu, T; Gorgen, A; Guttormsen, M; Hagen, TW; Kheswa, BV; Lui, YW; Negi, D; Ruud, IE; Shima, T; Siem, S; Takahisa, K; Tesileanu, O; Tornyi, TG; Tveten, GM; Wiedeking, M | Abstract:

Low-energy enhancement in the γ-ray strength functions of 73,74Ge

Author(s): Renstrom, T; Nyhus, HT; Utsunomiya, H; Schwengner, R; Goriely, S; Larsen, AC; Filipescu, DM; Gheorghe, I; Bernstein, LA; Bleuel, DL; Glodariu, T; Gorgen, A; Guttormsen, M; Hagen, TW; Kheswa, BV; Lui, YW; Negi, D; Ruud, IE; Shima, T; Siem, S; Takahisa, K; Tesileanu, O; Tornyi, TG; Tveten, GM; Wiedeking, M | Abstract:

Relative {sup 235}U(n,{gamma}) and (n,f) cross sections from {sup 235}U(d,p{gamma}) and (d,pf)

Author(s): Allmond, J.M. | Abstract: The internal surrogate ratio method allows for the determination of an unknown cross section, such as (n,y), relative to a better-known cross section, such as (n,f), by measuring the relative exitchannel probabilities of a surrogate reaction that proceeds through the same compound nucleus. The validity of the internal surrogate ratio method is tested by comparing the relative gamma and fission exit-channel probabilities of a 236U* compound nucleus, formed in the 235U(d,p) reaction, to the known 235U(n,y) and (n,f) cross sections. A model-independent method for measuring the gamma-channel yield is presented and used. PACS numbers: 24.87.+y, 24.75.+i, 24.50.+g, 25.85.Ge

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 .