J.R. Hughes

Collective and non-collective high-spin states in 115I

The 92Mo(27Al, 2p2n gamma ) reaction has been used to populate high-spin states in 115I. The dominant structures are associated with pi h112/(550)1/2- and pi g92/(404)9/2+ orbitals. At the highest spins, favoured states with Ipi =43/2- and 51/2-, associated with non-collective oblate configurations are yrast. The systematics of such states in the odd-A 115-121I isotopes are discussed.

Quadruple moment of the i13/2 intruder band in 139Gd

The Doppler shift attenuation method has been used to extract the mean quadruple moment of the nu i13/2 intruder band in 139Gd. From a centroid-shift analysis of the data, and using Braune stopping powers, a value for the intrinsic nuclear quadrupole moment of Q0 approximately=7.0 eb is suggested, corresponding to a deformation beta 2 approximately=0.35. Because of appreciable side-feeding into the band at each level, a lineshape analysis of the data has also been attempted, in which the time structure of the side-feeding has been allowed to vary. This analysis indicates that the side-feeding is significantly slower than the in-band cascade.

Studies of octupole structures in the isotopes 220,222Rn populated via α decay.

The nuclei 220,222Rn have been studied, using the alpha -radioactive sources 226Ra and 228Th, via the technique of alpha - gamma angular correlation. This has enabled Jpi assignments to be made to the previously known low-lying levels in 220,222Rn and alpha hindrance factors to be interpreted. The systematics of alpha hindrance factors for these Z=86 nuclei are examined and compared with those of Z=88, 90 nuclei. The subsequent alpha decays to 216,218Po were observed and 2+ assignments confirmed for the first excited states in these nuclei.

Prolate and oblate rotational bands in 136Sm

Six rotational bands have been established in 136Sm following heavy-ion induced reactions carried out at the Nuclear Structure Facility, Daresbury. The yrast band has been observed up to Ipi =(24+) and undergoes three band-crossings. A band was observed built on the low-lying 2+ gamma-vibrational state, in addition to two negative parity sidebands built on two-quasiproton excitations. A dipole band showing the characteristics of collective oblate rotation was also established. The results are discussed in terms of total Routhian surface and cranked Woods-Saxon model calculations.

Electromagnetic properties of N=75 isotones: evidence for triaxiality at low spin

Electromagnetic properties of the negative-parity yrast bands of the N=75 isotones ranging from barium to gadolinium (56<or=Z<or=64) are summarized. Experimental E2/M1 multipole mixing ratios for inband Delta I=1 transitions have been extracted up through the first band crossing, allowing the evaluation of B(M1; I to I-1)/B(E2; I to I-1), B(M1; I to I-1)/B(E2; I to I-2) and B(E2; I to I-1)/B(E2; I to I-2) ratios of reduced transition probabilities for both the nu h11/2 and nu h11/2(X)( pi h11/2)2 configurations. The results obtained at low spin provide evidence for triaxial nuclear shapes, while at high spin the data are consistent with axially symmetric shapes.

Band termination in doubly odd 116I

The 92Mo(27Al,2pn gamma ) reaction has been used to populate high-spin states in doubly odd 116I. Evidence for a termination of the collective rotational states is observed at spin Ipi =(23-). Total Routhian surface calculations have been performed in order to interpret the structure of this non-collective state which is found to be closely related to termination states seen in several neighbouring odd-A iodine isotopes.

First observation of a rotational band in oddSn50nuclei:Sn111

Proton particle-hole excitations across the {ital Z}=50 closed shell are responsible for inducing low-lying prolate deformation in even-{sub 50}Sn nuclei. Although related rotational bands have been studied in odd-{sub 51}Sb isotopes involving the coupling of a valence proton, none had been found in odd-{sub 50}Sn nuclei. Using the {sup 96}Ru({sup 19}F,3{ital pn}) reaction, a decoupled band has been observed in {sup 111}Sn extending to a spin-parity of (67/2{sup {minus}}) and feeding out at 23/2{sup {minus}} into spherical states. This band is interpreted as the {nu}{ital h}{sub 11/2} valence orbital coupled to the deformed [({pi}{ital g}{sub 7/2}){sup 2}{direct_product}({pi}{ital g}{sub 9/2}){sup {minus}2}] {sup 110}Sn core. The extracted band properties are compared to those in {sup 111}Sb with the same deformed core.

First observation of a rotational band in odd {sub 50}Sn nuclei: {sup 111}Sn

Proton particle-hole excitations across the {ital Z}=50 closed shell are responsible for inducing low-lying prolate deformation in even-{sub 50}Sn nuclei. Although related rotational bands have been studied in odd-{sub 51}Sb isotopes involving the coupling of a valence proton, none had been found in odd-{sub 50}Sn nuclei. Using the {sup 96}Ru({sup 19}F,3{ital pn}) reaction, a decoupled band has been observed in {sup 111}Sn extending to a spin-parity of (67/2{sup {minus}}) and feeding out at 23/2{sup {minus}} into spherical states. This band is interpreted as the {nu}{ital h}{sub 11/2} valence orbital coupled to the deformed [({pi}{ital g}{sub 7/2}){sup 2}{direct_product}({pi}{ital g}{sub 9/2}){sup {minus}2}] {sup 110}Sn core. The extracted band properties are compared to those in {sup 111}Sb with the same deformed core.