R. V. Ribas

Precise DSAM lifetime measurements in 48Cr and 50Cr as a test of large scale shell model calculations

Precise DSAM lifetime values have been obtained for the positive parity yrast bands of 48Cr and 50Cr, populated with the reaction 28Si+28Si at 115 MeV bombarding energy using a Au backed target. The obtained precision relies on the well-known stopping power at high velocity and on the use of DSAM analysis procedures which avoid the sidefeeding contribution. The deduced B(E2) and B(M1) values are in very good agreement with those predicted by full fp shell model (SM) calculations. A new procedure named narrow gate on transition below has been applied for the analysis of the lifetimes. Clear evidence was found in both nuclei for a low-lying negative parity band which has been successfully described by SM in the fp shell extended to include a hole in the 1d32 orbital. Also in this case the derived B(E2) and B(M1) values are in good agreement with the SM calculations.

Lifetimes of a shears band in 139Sm

Abstract Lifetimes have been measured in 139Sm with the DSAM method, using the reaction 62Ni(81Br,p3n)139Sm at 350 MeV. In the negative-parity regular dipole band based on the 25 2 − state at 3325 keV values of 0.60(21), 0.40(14) and 0.25(8) ps were found for the 337, 409 and 473 keV transitions, respectively. The deduced B(M1) and B(E2) are in agreement with the predictions of the tilted axis cranking model, allowing a triaxial equilibrium shape for the assumed νh 11 2 ⊗ πh 11 2 2 configuration.

Lifetimes in the middle of 1f7/2 shell: cross-conjugated nuclei 47V and 49Cr

DSAM lifetimes have been determined in the middle of 1f7/2 shell for the cross-conjugated nuclei 47 Va nd 49 Cr, populated with the reaction 28 Si on 28 Si at 115 MeV using a Au backed target. B(E2) and B(M1) reduced rates agree very well with large scale shell model predictions. The interplay between spherical and collective structures is discussed.  2001 Elsevier Science B.V. All rights reserved.

g-factors in the ground state and γ-bands in 164,166,168Er

Abstract The g -factors of the ground state band members up to the 10 + level and of the 2 + state in the γ-vibrational band have been measured in 164,166,168 Er using the Coulomb excitation transient field technique. In the g-band the g -factor values were found to be nearly constant as a function of spin. For the 2 + states of the γ-band, values about 20% larger than those in the g-band have been determined. This latter fact is consistent with the known decay properties of the γ-band.

Shape change along the highly-deformed band in 137Nd☆

Abstract Lifetimes of states of the highly-deformed (HD) band in 137Nd have been measured using the Doppler shift attenuation method. A line-shape analysis has been carried out for individual states, resulting in transition quadrupole moments which decrease with increasing spin. This represents the first confirmation of previous total routhian surface (TRS) calculations that predicted a drift towards positive γ values of the HD minimum (at essentially constant β deformation). The lifetime data show a rather modest deformation of the HD band structure, indicating a softening of the nuclear potential at HD shape.

SACI—a 4π plastic phoswich array ancillary detector system of a γ-ray spectrometer

A large solid angle low-Z charged particle detector system was built in order to improve the quality of the identification and selection of evaporation channels for in-beam g-spectroscopy measurements. The array consists of 11 plastic phoswich telescopes closely packed in a 4p arrangement and to be used as an ancillary system for the Pelletron Laboratory g-ray spectrometer. The new system was tested in g-particle and g–g-particle coincidence measurements using the 27 Al þ 16 O and 100 Mo þ 11 B reactions, at 53 and 43 MeV incident beam energies, respectively. The values for the particle detection efficiency and improvement in the peak to background ratios are considered acceptable for the usefulness of the system. r 2002 Elsevier Science B.V. All rights reserved.

Shape transition in odd-odd A ≈ 130 nuclei

Abstract A systematic analysis of rotational bands in doubly odd nuclei in the mass region A = 130–140 is carried out using a shell model configuration mixing approach. The shell model (many-body) basis is constructed by projecting out deformed quasiparticle (Nilsson + BCS) states onto good angular momenta. The hamiltonian is assumed to be a sum of (spherical) single-particle hamiltonian and a schematic two-body interaction, which consists of Q · Q + (monopole) pairing + quadrupole-pairing forces. The analysis indicates a shape transition from prolate ( N = 73) to oblate ( N = 79) shape as a function of neutron number. Agreement between theoretical results and experimental data is quite satisfactory except for γ-deformed nuclei ( N = 75 and 77).

Superdeformed band g-factor in 133Nd

Abstract A g-factor measurement in the superdeformed band of 133Nd has been performed by applying the transient field method in coincidence mode with the multidetector array GASP. The 133Nd nuclei were populated by the 104Pd(32S,2pn) reaction at a bombarding energy of 135 MeV. Polarized Gd has been used as ferromagnetic host. A mean g-factor of g = 0.31(8) has been determined at the I π = 41 2 + superdeformed state. The experimental value is compared with theoretical predictions and supports the assignment of the superdeformed band to the ν[660] 1 2 + Nilsson intruder orbital.

g-factors of the lowest 2+ and 4+ states in198, 200, 202Hg

Theg-factors of the 21+ and 41+ states in198,200,202Hg were simultaneously measured by means of the transient-field perturbed angular correlation method in Coulomb excitation using multi-isotopic targets and thin polarized Gd foils as ferromagnetic host. Theg(21+) andg(41+) were found identical within errors in198, 200Hg, while in200Hg lowerg-factor values have been determined. The experimentalg-factors were compared with the predictions of the pairing-plus-quadrupole, dynamical deformation and interacting boson models.

MagMo: data analysis of TMF measurements of g-factors

Abstract A computer code dedicated to data analysis of g -factor measurements of excited nuclear states using the transient magnetic field (TMF) is described. Although the code was conceived for the cases where multiple Coulomb excitation is used to populate the excited states, it may also be employed for fusion-evaporation reactions with transient or static interactions.