C.J. Pearson

The role of triaxiality in the ground states of even-even neutron-rich Ru isotopes

Abstract Partial decay schemes for the very neutron-rich nuclei 108,110,112 Ru and 114 Ru, about which nothing was previously known, have been determined from the study of prompt, triple-γ coincidences in 248 Cm fission fragments. Levels with probable spin up to 10ħ have been observed and γ-ray branching ratios obtained. Ratios of reduced electric quadrupole transition probabilities obtained from the branching ratios are in good agreement with predictions of a simple model of a rigid triaxial rotor.

Triple angular correlations of γ rays following spontaneous fission

Abstract Triple angular correlations between γ rays following spontaneous fission of 248 Cm are studied using the EUROGAM array. Results, for transitions in even-even fission-product nuclei, agree with predictions of angular correlation theory. Efficient detector systems combined with new analysis techniques offer for the first time a convenient tool to determine multipolarities of prompt γ transitions in the fission-product nuclei.

Search for octupole deformation in neutron-rich Cs nuclei

Abstract Partial level schemes of the very neutron-rich nuclei 141,143,145 Cs have been determined from the study of γ-γ-γ coincidences in 248 Cm fission fragments. Excited states of 143,145 Cs nuclei were observed for the first time. The possible existence of octupole deformation in the Cs nuclear ground states is discussed.

High-spin states in the neutron rich fission fragments138Xe and139Xe

High-spin structures in the neutron-rich nuclei138Xe and139Xe have been investigated by observing prompt γ -rays from the spontaneous fission of248Cm with the Eurogam spectrometer. The partial level schemes were constructed on the basis of double-, triple- and quadruple-γ coincidences. The ground state band in138Xe has been extended up to 5 MeV excitation energy. The structure of the newly observed medium-spin states in139Xe is similar to the one of heavier N=85 isotones where vf72/3, vh9/2f72/2 and vf72/3 ⊗ 3− multiplets have been observed.

Gamma-decays of 151Eu levels populated in the 150Nd(6Li, 5n) reaction

The N = 88 nucleus 151Eu was studied using the 150Nd (6Li, 5n) reaction, at a bombarding energy of 47 MeV, to populate yrast and near yrast levels at medium spins. A wide variety of bands was observed, including two that could be attributed to the coupling of an h112 proton to an octupole phonon. Although strong electric dipole transitions were observed, no good evidence was found for reflection-asymmetric band structures. This suggests that any tendency towards stable octupole deformation at low or medium spins is weak in this nucleus. Band structures were examined for evidence of triaxiality. The observations are consistent with but do not require a triaxial shape.

A spectrometer for prompt mass identification of fragments from low‐energy fission

A spectrometer for prompt mass identification of fragments from low‐energy fission having a large effective solid angle of 35.2 msr is described. The mass identification is obtained by time‐of‐flight measurement using a pair of microchannel plate detectors and kinetic energy measurement using an axial ionization chamber. A mass resolution of 3.8 u at 100 u was obtained from experiments which observed coincidences between fragments and γ rays from a 252Cf spontaneous fission source.

Search for octupole deformation in neutron-rich Xe isotopes

A search for octupole deformation in neutron-rich Xe isotopes has been conducted through prompt gammaray spectroscopy of secondary fragments produced in the spontaneous fission of248Cm. The spectrometer consisted of the Eurogam 1 array and a set of 5 LEPS detectors. Level schemes were constructed for Xe isotopes with mass number ranging from 140 to 144 and excited states for143,144Xe nuclei were observed for the first time. None of the level schemes exhibit an alternating parity quasimolecular band, a feature usually expected in nuclei in which octupole correlation effects are strong enough to produce stable octupole deformation. For several isotopes, structures observed in the level schemes are consistent with an octupole softness of the nuclei.