S. Brant

SU(6) quadrupole phonon model for even and odd nuclei and the SU(3) limit

Abstract Analogous to the equivalence between the SU(6) quadrupole-phonon model (TQM) and the interacting boson model (IBM), the equivalence is pointed out for odd systems between the SU(6) particle quadrupole-phonon coupling model (PTQM) and the interacting boson-fermion model (IBFM). PTQM is formulated starting from the Dyson representation for the odd system. Different aspects of the SU(3) limit of TQM and PTQM are studied; the quadrupole-phonon block structure of rotational bands in even and odd nuclei and analytic expressions based on the coherent state; signature effects generated in PTQM; electromagnetic properties and correction factors for PTQM; overlaps of the PTQM analogs of Nilsson states with Coriolis-coupled Nilsson states and the relation to the rotational model representation.

Asymptotic cancellation for the tensor M1 operator versus particle-vibration coupling away from doubly closed shell nuclei

Abstract For M1 transitions which are l -forbidden in zeroth order, asymptotic cancellation appears among second- and higher-order contributions to the matrix element of the tensor M1 operator. This leads to approximate reestablishment of the zeroth-order value, although the wave functions of the initial and final state are rather mixed.

SU(6) model for odd-odd nuclei (OTQM/IBOM) and boson-aligned phase diagram inO(6) limit

We introduce the SU(6) model IBOM/OTQM for odd-odd nuclei and discuss the bands in O(6) limit. Bands are characterized by a particular type of phase correlations in the wave functions and exhibit splitting of the SU(3) analogs of Gallagher-Moszkowski bands.

Nuclear structure of 198Au studied with (n, γ) and (d, p) reactions and interpreted with the IBFFM

Abstract The 197 Au(d, p) 198 Au reaction was measured with the high-resolution Q3D spectrograph at the Munich Tandem Accelerator at θ lab = 35°, using 20 MeV deuterons. Average resonance neutron capture gamma rays were measured with a filtered neutron beam at the Brookhaven National Laboratory. Using also secondary (n, γ) data a level scheme of 198 Au was established with 66 levels up to an excitation energy of 1600 keV mostly with spin and parity assignments. The level energies, E2 and M1 branching ratios and (d, p) transfer data were compared with new model predictions of the interacting boson-fermion-fermion model (IBFFM). This model provides a basic understanding of 198 Au.

Structure of 66Ga from (p, nγ) reaction

Abstract γ-ray, γγ-coincidence, and internal conversion electron spectra were measured with Ge(HP), as well as superconducting and traditional magnetic lens plus Si(Li) electron spectrometers at different bombarding proton energies between 6.5 and 7.1 MeV. Energies and relative intensities of 131 (among them 52 new) 66Ga γ-rays have been determined. Internal conversion coefficients of 33 transitions were measured for the first time. A more complete level scheme with new levels, γ-ray branching ratios, level spin and parity values has been deduced. The energy spectrum and electromagnetic properties were calculated on the basis of an interacting boson-fermion-fermion/truncated quadrupole phonon model for odd-odd nuclei. The model calculations reasonably describe the level spectra and electromagnetic properties of 64Zn, 65Ga, 65Zn and 66Ga nuclei with consistent parametrization.

Evolution from spherical to various deformed shapes in the odd-odd 59136Pr77 nucleus

Abstract The level scheme of the doubly odd 136Pr nucleus has been investigated via the 136Ce(p,n), 122Sn(19F,5n) and 110Pd(30Si,p3n) reactions at beam energies of 14, 84 and 125 MeV, respectively. A complex decay scheme has been established for the 90 ns isomeric level with Ex = 594.7 keV and Jπ = 6+. The two previously reported bands, one based on the πh 11 2 ⊗ νh 11 2 configuration and one with suggested negative parity consisting of only dipole transitions, have been extended at higher spins and connected firmly to the 6+ isomer. Six new bands have been also identified: two consist of strong dipole and crossover quadrupole transitions, whereas the other four, very weakly populated, consist of only quadrupole transitions. The observed level structures are compared to theoretical calculations performed within the interacting boson model for odd-odd nuclei (IBFFM) and the cranked shell model. The experimental B (M1) B (E2) ratios of the yrast band are well reproduced by the IBFFM calculations, while those of the other semi-decoupled structures are in good agreement with the values obtained from the semiclassical model of Donau.

Detailed spectroscopy and IBFFM interpretation of the odd-odd nuclei 132Pr and 130Pr

Abstract High-spin rotational structures in the odd-odd nuclei 130,132Pr have been studied via the 104 Pd + 32 S reaction at 160 MeV. Several states below the previously reported negative- and positive-parity states have been established through the observation of low-energy transitions, leading to new spin assignments for all observed levels. The bands based on the πh 11 2 ⊗ vg 7 2 and πh 11 2 ⊗ vh 11 2 configurations have been extended at much higher spins. Detailed interacting boson-fermion-fermion model calculations have been performed for the two nuclei, which reveal the complex structure of the new observed low-lying states. The change from inverted to normal signature at high spin and the staggering pattern of all observed bands are well reproduced, being explained by the interplay between a new term introduced in the boson quadrupole operator and the residual quadrupole-quadrupole interaction.

High-spin states in 137Nd: A large variety of collective rotations

Abstract The high-spin structure of 137Nd has been studied through the 110Pd(30Si,3n) and the 123Sb(19F,5n) reactions at beam energies of 125 and 97 MeV, respectively. A very complex level scheme has been established up to spin 97 2 + and 23.9 MeV of excitation energy. Regular bands are observed at high-spin, consisting of either M1 and E2 crossover transitions, or of stretched M1 or E2 transitions. Calculations have been performed in the framework of the interacting boson-fermion model with broken pairs for the relatively strong ΔI = 1 regular structures observed above spins 27 2 − and 31 2 − , which are well described by the (νh 11 2 ) 3 and νh 11 2 ⊗(πh 11 2 ) 2 configurations, respectively.

Levels of 137Ba studied with neutron-induced reactions

Abstract The nucleus 137 Ba has been studied via primary and secondary γ-rays as well as γγ-coincidences following thermal-neutron capture and inelastic neutron scattering. A level scheme was established up to 4.7 MeV consisting of 37 levels including 91 transitions. The neutron binding energy was determined to be 6905.59(8) keV. The thermal-neutron-capture cross section and isomer production of the 11 2 − state at 661.6 keV were determined to be 0.65 −0.04 +0.08 and 0.0098(4) b respectively. The experimental data on excitation energies and electromagnetic properties are compared with predictions of the SU(5) limit of the interacting boson-fermion model. A satisfactorily good agreement between experiment and theory can be stated.

Low-lying states in the doubly odd nucleus 132Pr from beta decay of 132Nd

Abstract The low-lying level scheme of the odd-odd nucleus 132Pr has been investigated for the first time. The radioactive nuclei were produced by bombarding 96Mo targets with a 225 MeV 40Ca beam. Levels in 132Pr have been populated from the 132Nd β-decay. A new value of its half-life has been measured: T 1 2 = 88 ± 7 s . The activities produced in the reaction have been transported with a He-jet device and γγt, Xγt, e−γt coincidence measurements performed. Internal conversion coefficients have been measured with a magnetic lens spectrometer. The experimental level scheme of 132Pr is compared to theoretical calculations performed with the interacting boson-fermion-fermion model (IBFFM).