J.A. Evans

An intrinsic spin for interacting bosons

Abstract The addition, to the usual set of T =1 bosons, of s and d bosons with T =0 and an intrinsic spin of S =1 leads to a version of the IBM which incorporates the Wigner supermultiplet symmetry.

A soluble γ-unstable hamiltonian

Abstract A simple five-dimensional hamiltonian for the nuclear shape is solved analytically for any value of a parameter whose variation describes vibration about a spherical equilibrium at one extreme and a rigid non-spherical but γ -unstable nucleus at the other. Spectra and E2 transition rates are compared with results from the interacting boson model.

An IBM-3 analysis of the nuclei just beyond the magic numbers N = Z = 28

Abstract The isospin-invariant form IBM-3 of the interacting boson model has been used to study energies and electromagnetic properties of the isotopes of nickel, zinc, germanium and selenium in the first half of the 1p 3 2 , 0f 5 2 and 1p 1 2 shell. The hamiltonian and electromagnetic operators vary with boson number and isospin in a manner determined by a mapping into the shell-model based on seniority and reduced isospin.

A microscopic derivation of the dependence of the IBM3 hamiltonian on the boson number and isospin

Abstract The number and isospin dependence of the hamiltonian in the isospin invariant form (IBM3) of the boson model has been deduced from a seniority mapping into a single j-shell, making use of shell-model formulae recently obtained from vector coherent state theory. Numerical results are given for a specific shell-model example and the qualitative behaviour of the different parameters in the hamiltonian is discussed.

A microscopically determined IBM 3 hamiltonian

Abstract An IBM 3 interaction is deduced from a four-nucleon shell-model calculation and the IBM results for six nucleons are compared with those of the shell-model. The relation between the shell-model interaction and the boson interaction is investigated and the quadrupole component of the shell-model interaction is seen to dominate the relative energies of states with different U(6) labels.

The group [R5] O(5) as a link between the O(6) limit of the IBM and the γ-unstable geometrical model

Abstract It is shown that for large boson number N the O(6) group of the interacting boson model contracts to the group [R5] O(5) of the rotor with fixed deformation.

Isospin in a boson approximation for particles and holes

Abstract With neutron holes and proton particles in the same j-shell (or vice-versa) it is shown that IBM 2 states have good isospin in the limit of large j. A relation is deducted between particle-hole signature and F -spin.

On the validity of the O(18) coupling scheme in N ∼ Z nuclei

Abstract Wave-functions from the newly proposed O(18) coupling scheme in IBM-3 are compared with those from a numerical calculation fitted to some Zn, Ge and Se nuclei.

An IBM-3 hamiltonian from a multi-j-shell model

Abstract The number and isospin dependence of the hamiltonian in the isospin invariant form (IBM-3) of the boson model is deduced from a seniority mapping onto a shell-model system of several shells. The numerical results are compared with earlier work for a single j -shell.

Electromagnetic operators in IBM-3 and their dependence on the boson number and isospin

Abstract A Marumori mapping from the isospin invariant form (IBM-3) of the interacting boson model into the shell model is used, with the help of the neutron-proton quasi-spin group O(5), to deduce the dependence of the IBM-3 electric quadrupole and magnetic dipole operators on the boson number and isospin. Some comparisons are made with IBM-1 and IBM-2.