S. Lunardi

Particle hole yrast states in146Gd and147Gd and the Z=64 shell closure

The level structures of146Gd and147Gd have been investigated by in-beamγ-ray ande− spectroscopy with (α, xn) reactions on enriched Sm targets. Detailed level schemes up to ∼4 MeV, which differ radically from earlier schemes, are reported. The energy levels are characterized as particle-hole excitations using empirical single particle energies and two nucleon interactions. Analysis of pure 1p 1h proton excitations demonstrates that theZ=64 andN=82 energy gaps are about equally large.

Structure of 52,54Ti and shell closures in neutron-rich nuclei above 48Ca

Abstract The level structure of 5422Ti32 has been explored for the first time by combining β-decay measurements from fragmentation products with prompt γ-ray spectroscopy following deep inelastic reactions. The latter technique was also instrumental in tracing 52Ti30 to higher spin. The data provide new tests of effective interactions for full pf-shell calculations in neutron-rich nuclei above 48Ca. The data indicate the presence of a significant subshell gap at N=32 and comparisons between theory and experiment suggest an additional shell closure at N=34 in Ca and Ti isotopes.

Heavy-ion fusion below the Coulomb barrier: The systems 28,30Si + 58,62,64Ni and 32,34,36S + 58,64Ni

Abstract Fusion cross-sections for the 12 systems 28,30 Si + 58,62,64 Ni and 32,34,36 S + 58,64 Ni were measured at many energies from well below up to about 1.5 times the Coluomb barriers. The data show large sub-barrier fusion probabilities with strong isotopic dependences. The results of coupled-channel calculations involving the lowest 2 + and 3 − levels of both colliding nuclei and the 2-neutron transfer channel are compared with the measured excitation functions. Indications for the importance of the transfer channels are found. Signatures of system-dependent effects of the positive Q -value transfer channels are evidenced, also from a systematic intercomparison of the data.

Rotational bands in the doubly odd nucleus 134Pr

Abstract The band structures of the doubly odd 134 Pr nucleus has been investigated via the 119 Sn( 19 F,4n) 134 Pr and 110 Pd( 28 Si,p3n) 134 Pr reactions at beam energies of 87 and 130 MeV, respectively. The three previously known rotational bands based on the π[541] 3 2 − (α=± 1 2 )⊗ν[514] 9 2 − and π[423] 5 2 + ⊗ν[514] 9 2 − configurations have been extended to higher spins. The difference of ≈2ħ in the experimental alignment of the bands based on the signature partners of the [541] 3 2 − h 11 2 proton orbital is discussed in terms of shape coexistence and coupling with the γ-phonon but no consistent interpretation can be found. A new band consisting of quadrupole transitions has also been identified and linked unambiguously to the low-lying levels of the yrast band. Total routhian surface and cranked shell model calculations suggest a (π h 11 2 ) 3 ⊗ν[530] 1 2 − configuration for this band. The experimental ratios of reduced transition probabilities B( M 1) B( E 2) of the various rotational structures are compared to the theoretical values obtained from a semiclassical model and from the two-particle plus triaxial-rotor model.

In-band M1 and E2 transition rates and collective structures in 128Ba

Abstract Subpicosecond mean lifetimes of eight excited states in 128Ba populated via the 96Zr(36S,4n) reaction were measured by the Doppler-shift attenuation (DSA) technique using a line-shape analysis. The differential decay-curve method (DDCM) was applied for the lifetime determination. The B(E2) values in the yrast band indicate that the first band-crossing is with a proton S-band. The configuration πh 11 2 d 5 2 of the negative-parity semi-decoupled bands is confirmed by the measured B(E2, I → I − 2) and B(M1, I → I − 1) transition strengths. The higher-lying “dipole” band in 128Ba can be described as a high-K four-quasiparticle band built on the prolate configuration (πh 11 2 d 5 2 ) ⊗ (νh 11 2 g 7 2 ) .

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.

Linking transitions between the highly deformed states and the yrast states of normal deformation in 133Nd

Abstract Transitions linking the highly deformed band to low deformation states have been unambiguously established in 133 Nd in the very first experiment performed with the GASP array. the highly deformed band becomes yrast at 29 2 + , where it mixes with the positive parity band built upon the [404] 7 2 Nilsson state. The experimentally deduced interaction amounts to 13 keV. The measurement of the spins in the highly deformed intruder band sheds some light upon the reported backbend anomaly in this mass region.

Band termination in the N = Z odd-odd nucleus

High spin states in the odd-odd N=Z nucleus 46V have been identified. At low spin, the T=1 isobaric analogue states of 46Ti are established up to I = 6+. Other high spin states, including the band terminating state, are tentatively assigned to the same T=1 band. The T=0 band built on the low-lying 3+ isomer is observed up to the 1f7/2-shell termination at I=15. Both signatures of a negative parity T=0 band are observed up to the terminating states at I = 16- and I = 17-, respectively. The structure of this band is interpreted as a particle-hole excitation from the 1d3/2 shell. Spherical shell model calculations are found to be in excellent agreement with the experimental results.

^{46}

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.

V.

Inbeam γ-ray angular distribution measurements establishIπ = 3− for the 1579 keV first excited state in146Gd.