Ni64 +92Zr fission yields at energies close to the Coulomb barrier

Fission yields for the Zr64 reaction at laboratory energies between 240 and 300 MeV have been measured. Elastic scattering angular distributions were also obtained and used to deduce the generalized total reaction cross sections. The competition between fission and light-particle evaporation from the compound nucleus is well reproduced by statistical-model calculations. However, the calculated neutron multiplicities for this reaction are larger than those previously measured. Possible reasons for this discrepancy are discussed

Decay history and magnetic moments at high spin in Dy152

Average magnetic moments as well as information on the time evolution of the continuum structure of Dy152 at high spin have been obtained using the transient hyperfine magnetic field acting on fast ions traversing a thin, magnetized gadolinium foil. Dy152 nuclei were populated by the Ge76(80Se,4n)152Dy fusion-evaporation reaction at E(80Se)=326.5 MeV. The target-ferromagnet arrangement corresponds to a time window of about 701200 keV, rays contributing to the collective E2 bump, exhibit a negligible precession, in accordance with the very short lifetimes of these states. The precession of the angular distribution of discrete yrast rays deexciting the nucleus from spin I35Latin small letter h with stroke down yields an average magnetic moment for states with 43Latin small letter h with strokeI31Latin small letter h with stroke. The resulting g=0.21(2) is considerably lower than the collective value Z/A0.43 and indicates an appreciable contribution from aligned neutrons to the lower-spin region populated within the above time frame. The results are discussed in the framework of model calculations of the -ray cascade

Additional evidence for fusion-fission in S32+24Mg reactions: Division of excitation energy and spin in the fission fragments

We have measured rays in coincidence with C12 fragments from the fission of Ni56 produced with the S32+24Mg reaction at Elab=140 MeV. These data provide insight into the fission process in this light system by giving information about the energy and spin sharing between the C12 and Ti44 fragments, and the spin alignment of the lighter, C12 fragment. The spin transfer and the nuclear temperature at scission deduced from this measurement can be related to the compound-nucleus spin and potential energy at scission. The results indicate a statistical decay process consistent with the predictions of the transition-state model employing newer estimates of the spin- and mass-asymmetry-dependent saddle-point energies and corresponding shapes. No evidence is found for the spin alignment of the C12 fragments, contrary to what might be expected for a deep-inelastic scattering origin of the fully energy damped yields

Observation of superdeformation in Hg191

The first observation of superdeformation in the mass region A190 is reported. A rotational band of twelve transitions with an average energy spacing of 37 keV, an average moment of inertia scrF(2) of 110 Latin small letter h with stroke2 MeV-1, and an average quadrupole moment of 183 e b has been observed in Hg191; this band persists at low rotational frequency. These results are in excellent agreement with a calculation that predicts an ellipsoidal axis ratio of 1.65:1 for the superdeformed shape in this nucleus

Superdeformed band in Hg192

The observation of a superdeformed band in the nucleus Hg192 is reported. The band has sixteen transitions with an average energy spacing of 36 keV and an average dynamic moment of inertia scrI(2) of 112 Latin small letter h with stroke2 MeV-1. This band persists to rather low rotational frequency (Latin small letter h with stroke0.125 MeV) and is proposed to extend in spin from 10+ to 42+. No transitions linking the superdeformed states and the low deformation yrast levels were found and the decay out of the superdeformed band appears to be statistical. This is the second case of superdeformation in the 190 region

Feeding of superdeformed bands: The mechanism and constraints on band energies and the well depth

Entry distributions leading to normal and superdeformed (SD) states in Hg192 have been measured. A model, based on Monte Carlo simulations of γ cascades, successfully reproduces the entry distribution for SD states, as well as all other known observables connected with the population of SD states. Comparison of experimental and model results, together with the measured SD entry distribution, suggest that the SD band lies 3.3-4.3 MeV above the normal yrast line when it decays around spin 10 and that the SD well depth is 3.5-4.5 MeV at spin 40

Measurement of single electron emission in two-phase xenon

We present the first measurements of the electroluminescence response to the emission of single electrons in a two-phase noble gas detector. Single ionization electrons generated in liquid xenon are detected in a thin gas layer during the 31-day background run of the ZEPLIN-II experiment, a two-phase xenon detector for WIMP dark matter searches. Both the pressure dependence and magnitude of the single-electron response are in agreement with previous measurements of electroluminescence yield in xenon. We discuss different photoionization processes as possible cause for the sample of single electrons studied in this work. This observation may have implications for the design and operation of future large-scale two-phase systems.Comment: 11 pages, 6 figure

Nucleon alignment in 191Hg. A competing mechanism at moderate spins

Detailed spectroscopic studies of the discrete γ-rays feeding and deexciting a 41 2-, 4.6 MeV level in 191Hg are reported. The resulting decay scheme indicates single-particle nature for the states above the 41 2- level. At moderate spin, the corresponding particle alignment mode competes favorably with collective oblate rotation. It is suggested that this sequence is associated with a non-collective prolate shape (ε{lunate}=0.1-0.15, γ≅-120°)

A superdeformed band in 151Dy

A rotational band of 19 (possibly 20) transitions extending to spin ∼ 131 2 h {combining short stroke overlay} has been observed in 151Dy with an average dynamic moment of inertia I(2) = 79 h {combining short stroke overlay}2 MeV-1. This band is identified as a superdeformed band in 151Dy. The value of I(2) agrees with cranked Strutinsky calculations. Similarities as well as striking differences with the superdeformed bands of neighboring nuclei are observed

Lifetime measurements in the superdeformed band of Hg192

Lifetimes were measured for transitions in the superdeformed band of Hg192 with the Doppler-shift attenuation method. The results yield an essentially constant quadrupole moment of 202 e b and indicate that the sidefeeding lifetimes are of the same order as the state lifetimes. The data are consistent with calculations using the cranked Woods-Saxon Strutinsky method with pairing