A study of states in 201, 203Tl using the (d, 3nγ) reaction: A new 92− band

The nuclei ^{201, 203} Tl were formed in (d, 3n) reactions. Studies of the de-excitation γ-rays are described and level schemes are deduced for both isotopes. Evidence is presented for the existence in ²⁰¹Tl of a rotational band built on the $\text{9}\text{2}{}^{\mathrm{?}}$ isomeric state at 920 keV. The band is compared to the $\text{9}\text{2}{}^{\mathrm{?}}$ bands occurring in the odd isotopes ^{191 ? 199}Tl and is shown to be well described by a symmetric rotor-plus-particle model. The model predictions for the low-lying positive parity states are also considered and satisfactory agreement with experimental data is obtained. No $\text{9}\text{2}$^? band was observed in ²⁰³Tl and possible interpretations of this result are presented.     

Angular momentum partition in heavy ion induced fission and the effects of shells on gamma-ray multiplicities

Gamma-ray multiplicities have been measured following fission of nuclei with a wide range of mass and angular momentum. The average multiplicity reflects the total angular momentum of the fragments, but the observed variation of multiplicity with fragment mass asymmetry is dominated by shell effects. The highest average multiplicity arises fission of the heaviest compound system, produced with the lowest angular moméntum. This behaviour is well described by spin enhancement through statistical excitation.     

Intrinsic states,high-spin rotational bands and rotation alignment in 177Os and 179Os

Low-lying intrinsic states and their associated rotational bands have been identified in ¹⁷⁷Os and ¹⁷⁹Os. They are the mixed i_{$\text{13}\text{2}$} neutron states and the $\text{1}\text{2}$^?[521] states in ¹⁷⁷Os and ¹⁷⁹Os, as well as the $\text{5}\text{2}$^?[512] state in ¹⁷⁷Os and the $\text{7}\text{2}$^?[514] state in ¹⁷⁹Os. The $\text{1}\text{2}$^? sta is assumed to be the ground state, the other intrinsic states giving rise to isomers. The in-band decay properties of the $\text{7}\text{2}$^?[514] band, and the i_{$\text{13}\text{2}$} bands show the effect of mixing. In the rotational bands in ¹⁷⁷Os a low frequency backbending anomaly is observed but no anomaly is observed in the i_{$\text{13}\text{2}$}. band. In ¹⁷⁹Os the i_{$\text{13}\text{2}$} band does backbend but at a higher frequency than in the yrast bands of the even neighbours. The systematics of the backbending frequencies, and the effects of blocking, are discussed. The rotation aligned angular momentum is deduced, and a comparison made between the i_{$\text{13}\text{2}$} bands and the s-bands in the even neighbours. The results broadly support the identification of the s-bands with the aligned (i_{$\text{13}\text{2}$})² configuration.     

High-spin states in 208Rn

The yrast decay scheme of ²⁰⁸Rn has been investigated up to spin $\text{≈ 20}\text{h}\text{?}$ and an excitation energy of ≈ 6 MeV. Several different γ-ray spectroscopic techniques were used to determine the properties of excited states and transitions in the nucleus. Significant changes to the previously established level scheme are proposed, based on the existence of an unobserved 3.1 keV transition. Simple empirical shell-model calculations of level energies aided in the assignment of shell-model configurations to excited states and the decay scheme is discussed in terms of these configurations. The energy level systematics for the even radon isotopes, from A = 206 to 212 are discussed, as are core polarization effects in the even radon isotopes (A = 204 to 210) and polonium isotopes (A = 202–208).     

Exotic Isomers in Deformed Atomic Nuclei

Excited states of atomic nuclei can have long half lives, due to the angular-momentum couplings of unpaired nucleons. Such isomeric states provide opportunities for exploring novel nuclear physics, astrophysics and physics at the atomic/nuclear interface. This review focuses on the properties of isomers in deformed nuclei, and emphasises the importance of axial symmetry in preserving the integrity of the K quantum number. A region of neutron-rich nuclei around ¹⁸⁸Hf (Z=72, N=116) is predicted to have exceptional isomer properties, and experimental advances are now opening up this region to detailed investigation. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the character of three 8+ states in 192Pb

Three low-lying 8⁺ states have been identified in ¹⁹²Pb . A newly observed cascade of $ \gamma$ -rays built directly on the 8⁺ ₁ state is compared to the previously identified, weakly rotational band above the 11^- $ \pi$ i _13/2 , h _9/2 isomer in the same nucleus, and to analogous structures in ¹⁹⁴Pb . The similarity of all four structures lends support to the suggestion that the 8⁺ ₁ configurations are of a similar oblate deformation to the 11^- isomers. The excitation energies of all three 8⁺ states in ¹⁹²Pb and ¹⁹⁰Pb are compared to systematics. The possibility that one of the 8⁺ states in ¹⁹²Pb is associated with a prolate shape is discounted.     

A parallel multi-configuration self-consistent field algorithm

A scalable multi-configuration self-consistent field (MCSCF) algorithm is described. The method for optimizing the orbital and configurational parameters is based upon the two-step Newton–Raphson approach with an augmented orbital Hessian matrix. A single copy of the two-electron integrals in the molecular orbital basis is distributed over the memory of all processors. Storage of the augmented Hessian is avoided by re-computing its elements as needed. A replicated data approach is used to parallelize the configuration interaction step. Scalability to 1024 processors is demonstrated.     

Microsecond isomers in 187Tl and 188Pb

Lifetime measurements of states in nuclei with A=187 and 188 have been performed, using reactions between ¹⁵⁵Gd and ³⁶Ar and following the transport of evaporation residues to the focal plane of a gas-filled recoil separator. In a separate experiment using the ¹⁵⁹Tb(³²S, 4n) reaction the γ-decay of isomeric levels in ¹⁸⁷Tl has been studied using delayed γ-γ coincidence measurements. From observation of their subsequent γ decay, the mean lifetimes were measured to be 1000 ± 55 ns and 1600 ± 100 ns. Although it was not possible to characterize the isomers completely, they are proposed as candidates for one-proton, two-neutron excitations. In the course of this study, the decay of an isomer in ¹⁸⁸Pb was also observed and its lifetime was measured as 1150 ± 30 ns, and limits of 20–600 ns were placed on the meanlife of an isomer conjectured in ¹⁸⁷Pb. Received: 20 August 1999     

The yrast spectroscopy of 209Rn

The yrast spectroscopy of ²⁰⁹Rn has been investigated to an excitation energy of over 7 MeV and to a spin of $\text{51}\text{2}$. The existence of six isomers has been established: $\text{1174}\text{keV}\text{(J}{}^{\mathrm{\pi }}\text{=}\text{13}\text{2}{}^{\mathrm{+}}\text{, τ}{}_{\mathrm{<mtext>m</mtext>}}\text{= 19.3 ± 1.9 μ}\text{s}\text{), 1687}\text{keV}\text{(}\text{19}\text{2}{}^{\mathrm{?}}\text{, 1.0 ± 0.3}\text{ns}\text{), 2419}\text{keV}\text{(}\text{21}\text{2}{}^{\mathrm{+}}\text{, 12.6 ± 0.3}\text{ns}\text{20 ± 3}\text{ns}\text{, 3637}\text{keV}\text{(}\text{35}\text{2}\text{, 4.3 ± 0.4 μ}\text{s}\text{)}\text{and}\text{4834}\text{keV}\text{(}\text{41}\text{2}{}^{\mathrm{?}}\text{, 14.4 ± 0.5}\text{ns}\text{)}$. Shell-model calcu are used to explain the observed structure. E3 and M2 transitions in ²⁰⁹Rn and neighbouring nuclei are discussed.