A.R. Poletti

Shape coexistence in very neutron-deficient Pt isotopes

Yrast bands in 176Pt(N=98) and 178Pt have been identified. The level scheme of 176Pt changes from a quasi-vibrational pattern to that of a well deformed rotor, at very low spins, a behaviour similar to that attributed to shape coexistence in the light Hg isotopes. Analysis of The 176-188Pt yrast bands supports a shape coexistence interpretation, the excitation energy of the intruder state behaving as predicted by Wood, (1981).

Spectroscopy of high-spin states in 211,212,213Fr

Abstract The level structures of 211 Fr, 212 Fr and 213 Fr have been observed to high spins, ~ 28 /kh, (and excitation energies ~ 8 MeV) using a variety of γ-ray spectroscopic techniques. The structure of these nuclides is discussed in terms of couplings of single-particle states through empirical shell-model calculations. Good agreement with experiment is obtained. In 212 Fr and 213 Fr core-excited configurations are required to explain the properties of the highest states. A number of long-lived states were observed in each nucleus some of which decay by enhanced E3 transitions. The E3 transition strengths are discussed.

g-Factors in 210Rn and octupole coupling of core-excited states in 210Rn, 211Rn and 212Rn

Abstract The g -factors of isomeric states in 210 Rn have been measured using the TDPAD technique. Semi-empirical shell-model calculations, with explicit inclusion of the couplings to the 3 − octupole vibration, are carried out for the core-excited states in 210 Rn and 211,212 Rn. The resulting mixed multi-particle configurations are used to explain simultaneously the g -factors and enhanced E3 transitions which connect several pairs of these states.

Magnetic moments, E3 transitions and the structure of high-spin core excited states in 211Rn

Abstract The results of g -factor measurements of high-spin states in 211 Rn are: E x = 8856 + Δ′ keV (J π = 63 2 − ) , g = 0.626(7); 6101 + Δ′ KeV ( 49 2 + ), 0.766(8) ; 5347 + Δ′ KeV ( 43 2 − ), 0.74(2) ; 3927 + Δ KeV ( 35 2 + ), 1.017(12) ; 1578 + Δ KeV ( 17 2 − ), 0.912(9) . These results together with measured E3 transition strengths and shell model calculations are used to assign configurations to the core excited states in 211 Rn. Mixed configurations are required to explain the g -factors and enhanced E3 strengths simultaneously.

High-spin yrast isomer in 211Rn and 212Rn with enhanced E3 decays

Abstract New isomeric states with Jπ = 69/2+, τm = 13(1) ns in 211Rn and Jπ = 33−, πm = 7(1) ns in 212Rn have been identified. They decay by enhanced E3 transitions with strengths of 33(3) and 43(6) single particle units to the known 63/2− and 30+ isomers in 211Rn and 212Rn, respectively. The excitation energies and transition strengths agree well with predictions of the multiparticle, octupole-vibration coupled model.

Spectroscopy and shell model interpretation of high-spin states in the N = 126 nucleus 214Ra

Abstract Excited states in the N = 126 nucleus 214 Ra have been studied using γ-ray and electron spectroscopy following reactions of 12 C and 13 C on 206 Pb targets. Levels were identified to spins of ∼ 25 ħ and excitation energies of ∼ 7.8 MeV. Lifetimes and magnetic moments were measured for several levels, including a spin (25 − ) core-excited isomer at 6577.0 keV with τ = 184 ± 5 ns and g = 0.66 ± 0.01. The level scheme, lifetime and magnetic moment data are compared with, and discussed in terms of, empirical shell-model calculations and multiparticle octupole-coupled shell-model calculations. In general, the experimental data are well described by the empirical shell model.

Spectroscopy of 166W and 167W and alignment effects in very neutron-deficient tungsten nuclei

Abstract High-spin states in 166 W and 167 W were populated by the reactions 142 Nd( 28 Si,4n) 166 W, 142 Nd( 28 Si,3n) 167 W and 147 Sm( 24 Mg,4n) 167 W. From the γ-decay the yrast band and a side band (with assumed negative parity) were identified to high spins. There is evidence for a second side band in 167 W. The observed backbend of the yrast sequences and band-crossing anomalies in the side bands are discussed in conjunction with cranked-shell-model calculations. A systematic comparison is made between the yrast bands of 166,167,168 W in order to understand the structure of the second backbend in 168 W.

Gamma decay and band structures in 46Ti

The states of 46Ti have been studied using the 43Ca( alpha ,n gamma ) reaction. The level and decay scheme of 46Ti was deduced from gamma - gamma coincidence, gamma -ray energy and intensity measurements. Spins are suggested on the basis of the gamma -ray angular distribution, supported by relative excitation functions. The ground-state band has been extended to spin 10+, and about 20 new states are observed. Some of these can be grouped into rotational-like bands based on the 3- state at 3.059 MeV and other excited states.

Spectroscopy of 211Rn approaching the valence limit

Abstract High-spin states in 211 Rn were populated using the reaction 198 Pt( 18 O, 5n) at 96 MeV. Their decay was studied using γ-ray and electron spectroscopy. The known level scheme is extended up to a spin of greater than 69 2 and many non-yrast states are added. Semi-empirical shell-model calculations and the properties of related states in 210 Rn and 212 Rn are used to assign configurations to some of the non-yrast states. The properties of the high-spin states observed are compared to the predictions of the multi-particle octupole-coupling model and the semi-empirical shell model. The maximum reasonable spin available from the valence particles and holes in 77 2 and states are observed to near this limit.

Incomplete-fusion reactions for γ-ray spectroscopy: Application to the study of high-spin states in 234U

Incomplete-fusion reactions occur when breakup of the projectile results in only part of the beam particle fusing with the target, the remnant being emitted with an energy equivalent to the beam velocity. Such reactions have been demonstrated to populate slightly neutron-rich nuclei compared to conventional fusion-evaporation reactions, opening possibilities for the study of nuclei along the neutron-rich side of the line of stability. Results from a study of 211Po are presented to illustrate the use of incomplete-fusion reactions for γ-ray spectroscopy. New results from a test-run which populated high-spin states in 234U via the 232Th(9Be,α3n) reaction are also presented. An interesting feature of the latter reaction is that the high fission probabilities for the compound nuclei which follow complete fusion, results in the residues from incomplete fusion forming the dominant residue channels.