D. A. Meyer

Systematic exploration of 0 + states in structurally diverse nuclei

The puzzling nature of 0 + excitations, especially in transitional and deformed nuclei, has attracted new attention. Following a recent experiment studying 158 Gd, we investigated 15 additional nuclei in and near the rare earth region. Our aim was to map out the energies of as many 0 + states as possible. A series of (p, t) experiments was performed at the Q3D magnetic spectrograph at the University of Munich MP tandem accelerator laboratory. These reactions are particularly sensitive to 0 + states. Outgoing tritons were recorded at various lab angles, and their relative cross sections are compared to those calculated using the distorted wave Bom approximation (DWBA). The L = 0 angular distribution is easily discerned. New 0 + states are found in each of these nuclei, and their systematics are discussed.

SASSYER: An old instrument for new physics at Yale

Abstract The Wright Nuclear Structure Laboratory has recently acquired a gas-filled recoil separator previously used at Berkeley National Laboratory for heavy-element synthesis. The separator will be used to separate reaction recoils from primary beam particles and fission products following target bombardment. Commissioning of the separator has recently been completed, and the structure of 203 Rn investigated.

High-resolution study of 0+ and 2+ excitations in 168Er with the (p, t) reaction

Excited states in the deformed nucleus 168Er have been studied with high energy resolution in the (p, t) reaction, with the Munich Q3D spectrograph. A large number of excited 0+ states (25) and 2+ states (64) have been assigned up to 4.0-MeV excitation energy. This allows detailed investigations along two directions of current interest: first, an extension of microscopic model interpretations into the region of medium level density above the pairing gap; second, a first analysis of the statistical fluctuation (order/chaos) properties of pure sequences of levels, in one deformed nucleus. Predictions of two models (the quasiparticle-phonon model and the projected shell model) are compared to the data, and it is concluded that, in both cases, mixing of more configurations is required in the wave functions.

Violations of K‐Conservation in 178Hf

Coulomb excitation of Kπ=6+(t1/2=77 ns), 8−(t1/2=4.0 s) and 16+(t1/2=31 y) 178Hf isomers has led to the measurement of a set of Eλ matrix elements, coupling the isomer bands to the γ‐ and ground state bands. The resulting matrix elements, derived using a coupled‐channel semiclassical Coulomb excitation search code, have been used to probe the K‐components in the wave functions and revealed the onset and saturation of K‐mixing in low‐K bands, whereas K‐mixing is negligible in the high‐K bands. The implications can be applied to other quadrupole‐deformed nuclei. An upper limit on the Coulomb depopulation yield of the 16+ isomer was calculated based on the present set of matrix elements.

Quadrupole moment measurements of TSD1 and TSD2 bands in 167Lu

The triaxial strongly deformed (TSD) bands in 167Lu were populated by the 123Sb(48Ca, 4n) reaction with a beam energy of 203 MeV. Gamma rays, requiring five fold or more in prompt coincidence, were detected with the Gammasphere spectrometer. Of particular interests are TSD bands 1 and 2 which have previously been interpreted as zero phonon and one phonon wobbling bands, respectively. Using the Doppler shift attenuation method (DSAM), a preliminary transition quadrupole moment of 6.9+0.3−0.3 eb was extracted for the TSD1 band. Data analysis continues for TSD2 which is considerably more weakly populated.

Isomers and seniority in the trans-Pb nuclei

Low-energy excited states of 210 Ra and 208 Ra were investigated at the Wright Nuclear Structure Laboratory of Yale University. Fusion evaporation recoils were selected using the gas-filled spectrometer, SASSYER. Delayed γ-rays, following isomeric decays, were detected at the focal plane of SASSYER with a small array of HPGe detectors. Transitions following the proposed J π = 8 + isomers were observed, and the half-lives measured. The experiments are discussed and results compared to expectations from the seniority scheme.

Surrogate Nuclear Reactions using STARS

The results from two surrogate reaction experiments using the STARS (Silicon Telescope Array for Reaction Studies) spectrometer are presented. The surrogate method involves measuring the particle and/or γ‐ray decay probabilities of excited nuclei populated via a direct reaction. These probabilities can then be used to deduce neutron‐induced reaction cross sections that lead to the same compound nuclei. In the first experiment STARS coupled to the GAMMASPHERE γ‐ray spectrometer successfully reproduce surrogate (n,γ), (n,n′γ) and (n,2nγ) cross sections on 155,156Gd using 3He‐induced reactions. In the second series of experiments an energetic deuteron beam from the ESTU tandem at the Wright Nuclear Structure Lab at Yale University was used to obtain the ratio of fission probabilities for 238U/236U and 237U/239U populated using the 236,238U(d,d′f) and 236,238U(d,pf) reactions. Results from these experiments are presented and the implications for the surrogate reaction technique are discussed.

High-resolution study of 0{sup +} states in {sup 170}Yb

Recently,

A First Test of the E(5/4) Bose‐Fermi Symmetry : 135Ba

{0}^{+}

High-resolution study of 0{sup +} and 2{sup +} excitations in {sup 168}Er with the (p, t) reaction

excitations, especially in the rare-earth region, were studied extensively. We extend this work by studying the excited