Peter von Brentano

IBM-2 calculations of even-even Pd nuclei

Abstract Excitation energies, electromagnetic transition strengths and static moments in even-even Pd nuclei have been described systematically by using the proton-neutron interacting boson model (IBM-2). Parameters are fitted so as to be consistent with microscopic calculations. Mixed symmetry 2 + states have been identified using the M1 transition strength. The F -spin impurity of the first 2 + state is investigated by means of g -factors and M1 transitions. The calculations have been extended to neutron-rich Pd isotopes with A > 116 for which excited states are still not known.

Excited states in124Xe

Excited states of124Xe have been investigated via the122Te(α, 2n),114Cd(13C, 3n) and108Pd(19F, p2n) reactions using in-beam gamma-ray and electron spectroscopy methods. 36 new levels and several spin and parity assignments were established, revealing the existence of at least one positive parity superband and two negative parity bands, one of them showing backbending.

On the mixing of two bound and unbound levels: Energy repulsion and width attraction

Abstract The mixing of two unbound levels is discussed in the frame of a non-hermitian effective Hamiltonian. For a real off-diagonal interaction energy repulsion and width attraction are found. Three examples of this phenomenon are discussed: The 2 + doublet at 17 MeV in 8 Be, a possible K s - σ -mixing and the ϱ-ω-mixing.

Band structure of even-even selenium isotopes in the proton-neutron interacting Boson model

Available systematic IBM calculations [1-6] for Krypton and Strontium isotopes have been extended to Selenium. The analysis in terms of the IBM is complicated by the interplay of collective and noncollective degrees of freedom. However, satisfactory agreement has been obtained forN≦42.

Energy repulsion and width attraction in a system of two interacting resonances in 8Be

Abstract It is shown that the effective hamiltonian associated with the S -matrix of a system of two interacting resonancea can be decomposed in a natural and unique way into a diagonal “unperturbed” effective hamiltonian and a real and purely off-diagonal interaction. The complex energies of the poles of the “perturbed” system exhibit energy repulsion and width attraction as compared to the poles of the “unperturbed” system. An example in 8 Be is given.

E1 transitions in rare earth nuclei and the SPDF boson model

Electric-dipole (E1) transitions between low-lying states of well deformed rare-earth nuclei are investigated using an SPDF boson model. The model can treat both the high-lying Giant Dipole Resonance (GDR) and the low-lying octupole vibrational bands. The p-boson is related to the GDR state while the f-boson is to the octupole vibration. The E1 operator T(E1) consists of p and f boson terms; the two p boson terms are determined by the experimental data on the GDR states. The remaining ƒ → d E1 transition charge is determined by fitting experimental B(E1) values between low-lying collective states. The present method has been applied to 156Gd, whose low-energy positive parity bands are well described by the SU(3) limit of IBM. It has been found that the E1 operator determined in this way gives the spin dependence of the B(E1) branching ratios close to the experimental results.

Classical analogy to quantum mechanical level repulsion

The frequency repulsion in coupled harmonic oscillators can be treated as a classical analogy to the quantum mechanical level repulsion. As an example the inductively coupled LC circuit will be discussed.

M1-matrix elements and F-spin symmetry in nuclei

Abstract In this paper we test the sensitivity of different matrix elements to F-spin admixtures in nuclei. Exact calculations of neutron and proton matrix elements are compared to those in the intrinsic formalism.

Average level repulsion for N narrow resonances and its application to 53Cr

Abstract It is shown that a real, symmetrical and off diagonal interaction among a set of N resonances leads to an average level repulsion if the resonances are sufficiently narrow as compared to the interaction strength. The result is a generalization of the level repulsion theorem from two bound states to N narrow resonances. A physical example is found in the neutron resonances in 53Cr.

Energy attraction and width repulsion due to external mixing and an application to 8Be

Abstract It is shown that the effective hamiltonian of a system of two unbound states with only one open reaction channel can be decomposed in a natural and unique way into a diagonal “unperturbed” effective hamiltonian and an off-diagonal interaction, which is either real or imaginary. Due to the imaginary interaction the complex energies of the “perturbed” hamiltonian exhibit energy attraction and width repulsion as compared to the energies of the “unperturbed” hamiltonian. An application to a doublet in 8 Be is given.