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The He 3 ( α , γ ) Be 7 process is a key reaction in both Big-Bang nucleosynthesis and p–p chain of Hydrogen Burning in Stars. A new measurement of the He 3 ( α , γ ) Be 7 cross section has been performed at the INFN Gran Sasso underground laboratory by both the activation and the prompt γ detection methods. The present work reports full details of the prompt γ detection experiment, focusing on the determination of the systematic uncertainty. The final data, including activation measurements at LUNA, are compared with the results of the last generation experiments and two different theoretical models are used to obtain the S-factor at solar energies.

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.

High-spin states in the neutron-deficient nuclide I-111 have been populated with the fusion reaction Ni-58 + Ni-58 at a beam energy of 210 MeV, in an experiment performed at the Tandem Accelerator of the Laboratori Nazionali di Legnaro. The gamma spectrometer GASP was used in time coincidence with the ISIS Si-ball and the CAMEL recoil mass spectrometer for the positive identification of the nuclide. Gamma transitions and structure details previously attributed to I-111 by Other authors are only partially confirmed. The obtained level scheme includes new rotational bands and a new low lying structure which suggests the presence of octupole correlations at predicted rotational frequency values.

The next generation of 4 pi arrays for high-precision gamma -ray spectroscopy will involve gamma -ray tracking detectors. They consist of high-fold segmented Ge detectors and a front-end electronics, based on new digital signal processing techniques, which allows to extract energy, timing and spatial information for a gamma -ray by pulse shape analysis of the Ge detector signals. Utilizing the information on the positions of the interaction points and the energies released at each point the tracks of the gamma -rays in a Ge shell can be reconstructed in three dimensions.

The lifetimes of five levels of the two-quasineutron band in 128 Ba populated via the 116 Cd( 16 O ,4 n) reaction were measured for the first time by means of the recoil-distance Doppler-shift method. For the data-analysis, a new version of the differential decay-curve method in singles-like mode was developed which takes into account the velocity distribution of the recoils and the effect of the Doppler-shift attenuation in the stopper. The high values of 〈K 2 〉 and K eff characterising the band are confirmed by the determined B (E2 ,I→I−2 ) and B (M1 ,I→I−1 ) transition strengths. At the same time, the rigid-rotor model is not able to describe the behaviour of the experimental B (E2 ,I→I−1 ) and B (M1 ,I→I−1 ) values. A new theoretical effort seems to be needed for a consistent explanation of the intraband transition strengths within two-quasiparticle bands in γ -soft nuclei.

A superdeformed band has been discovered in 143Gd consisting of 15 transitions. It does not show the band crossing observed in the neighbouring heavier Gd isotopes and it is degenerate with the superdeformed band in 143Eu. In contrast to other degenerate bands at superdeformed shape, the configurations of the bands are quite different here. They result from the exchange of a ν64 with a π[404]9/2 configuration. In addition, a collective band has been observed which adopts a well-deformed triaxial shape at high spins according to calculations. The transition from highly to superdeformed shapes proceeds via triaxial shapes.

High-spin states in 180Os have been populated by means of the 150Nd(36S,6n) reaction at 177 MeV and studied with the γ-spectrometers OSIRIS and GASP. Eight known bands have been extended to higher spins and a new strongly coupled band has been discovered. Configuration assignments of the bands have been carried out in the framework of the tilted-axis cranking model utilizing experimental ratios of reduced transition probabilities B( M1 ) B( E2 ) . The investigation of the alignment behaviour of the bands revealed that besides the well-known first band crossing caused by the alignment of an i 13 2 quasineutron pair, a second band crossing occurs in four of the bands. The crossing frequency is ⩾ 0.38 MeV and the alignment gain is fairly small, ranging between 2 and ⩾4 ℏ;. The crossing can consistently be explained as a two-quasineutron (ν 7 2 − [514]) 2 alignment. This crossing has been observed for the first time.

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 ) .

The g -factors and quadrupole moments of the 9 2 − isomeric states in 129,131 Ce have been determined by the TDPAD method. The results are g = −0.185(10) and | Q | = 1.32(13) eb for 129 Ce and g = −0.189(7) and | Q | = 0.92(10) eb for 131 Ce. Firm spin-parity assignments were made on the basis of measured moments. The experimental electromagnetic moments and the level energies in the positive- and negative-parity bands were analysed within the particle-plus-triaxial-rotor model and optimum shape parameters have been established.

Thick target γγ coincidence measurements for the system 130 Te + 275 MeV 64 Ni have been performed using the GASP Ge detector array at Legnaro. For the isotopic assignments of previously unknown γ-ray cascades, prompt γγ coincidences observed between Te and Ni partner products were of vital importance. The results yield much new information about excited states of moderate spins in A = 126–131 tellurium nuclei, especially about yrast excitations of the little studied odd- A isotopes 127 Te, 129 Te, and 131 Te. Level systematics of tellurium nuclei are presented, and both single-particle and collective aspects of the level spectra are discussed.

Five superdeformed (SD) bands have been identified in 144Gd with the GASP array using the reaction 100 Mo + 48 Ti . The J(2) moments of inertia of the four excited SD bands are flat as a function of rotational frequency, indicating the blocking of the N = 6 proton crossing observed in the yrast SD band. According to cranked shell model calculations, the excited bands have two-quasiproton configurations with one proton in the N = 6 orbital and the other in each signature partner of the [404]9 2 + or [411]3 2 + orbitals, lying above the Z = 64 gap. The interpretation of the excited SD bands in terms of proton excitations points to the high stability of the N = 80 shell closure at SD shapes. The population of the yrast SD band as a function of the beam energy has been also investigated. Our data shows that the intensity of the yrast SD band is not configuration dependent, being comparable to that of yrast SD bands in the neighboring nuclei. By comparing experimental and theoretical alignments, spins and configurations are assigned to all observed SD bands in the A = 140–150 region.

Using the (18O,5n) 163Er reaction a multitude of rotational bands have been established with firm spin and parity assignments in 163Er. In 17 out of 24 band crossings E2 cross-band transitions have been observed. The interaction strength varies between ∼ 1 and ∼ 50 keV with many of the values in the range 10–15 keV. These interactions sample a variety of the lowest (multi) -quasiparticle configurations. For some bands, in particular those with high K-values, the configurations can be established rather well. Quite complicated changes in the wavefunctions must occur at these crossings, and to explain the observed interaction strengths coupling to various vibrational degrees of freedom, in addition to possible residual neutron-proton interactions, may be needed.

Three bands consisting of dipole M1 and quadrupole E2 crossover transitions have been identified in 134 Nd using the GASP array and the 110 Pd( 28 Si, 4n) reaction at 130 MeV. Calculations with the projected shell model are used to assign configurations to the different bands and to infer their K -composition. The properties of the band built on the I π = 8 − isomer confirm the previously assigned two-quasineutron [404] 7 2 + ⊗ [514] 9 2 − configuration of the isomeric state. The other two bands are interpreted as coexisting prolate and oblate four-quasiparticle configurations.

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.

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.

Unfavored components of doubly decoupled bands are reported for the first time. They can be interpreted as having the pseudo-spin flipped relative to the orientation in the favored components, i.e. antialigned with respect to the rotation axis. In addition, the differences in consecutive transition energies along the favored and unfavored sequences are strikingly similar among them up to Iπ = 15+and 14+ respectively. This feature arises from a cancellation of differences in alignments and moments of inertia.

The high-spin states in 45 Sc were studied with the GASP multidetector array. The nuclei were excited by the 30 Si( 18 O,p2n) 45 Sc reaction at E LAB =60 MeV and separated with the Recoil Mass Spectrometer. Several new high-spin levels extending the known single-particle and collective structures were observed. Energies of the negative-parity states agree with the shell model predictions whereas the positive-parity-intruder rotational band extends up to very high rotational frequencies and continues beyond the maximum angular momentum available from the single-particle f 7 2 configuration.

Very proton rich nuclei in the A≈100 region have been investigated using the GASP array coupled with the Recoil Mass Spectrometer (RMS) and the GASP Si-ball. High-spin states of 105Sn and 103In nuclei formed with the reaction 58 Ni + 50 Cr at 210 MeV have been investigated up to ≈ 10 and 7 MeV of excitation energy respectively. We have confirmed the known excited states for both nuclei and extended to higher spin the level scheme. The experimental level schemes are compared with shell model calculations.

The hyperdeformed ridge structure recently observed in the reaction of 187 MeV 37 Cl on 120 Sn has been confirmed in a new proton-γ coincidence experiment at the GASP spectrometer and assigned to the nucleus 152 Dy. Proton spectra have been measured in coincidence with γ-rays belongings to the different structures in 152 Dy (oblate, prolate, super- and hyper-deformed). The deformation of the final evaporation residue affects only weakly the proton evaporation from the compound nucleus. Evidence has been found that the energy of the protons in coincidence with the hyperdeformed structure is larger than expected. This effect is discussed in the framework of the fission-evaporation competition.

The decay properties and the magnetic moment of the 548 keV isomeric state in 136Pr populated in the 122Sn (19F, 5n) reaction were investigated by pulsed beam γ-ray spectroscopy and TDPAD measurements using as host metallic Pt at room temperature. The determined characteristics of the isomeric state, T12 = 90(2) ns, Jπ = 4+ and g = + 0.570(19), are explained by assigning to it a dominant configuration π(1h112)⊗ν(1h112) and an extremely small contribution of configurations involving proton and neutron positive-parity orbits. Firm spin assignment for the upper energy collective structures can be deduced.

Gyromagnetic ratios of the 2 1 + and 4 1 + states in 192,194,196 Pt and of the 2 2 + states in 192,194 Pt were simultaneously measured by the transient-field perturbed angular correlation method in Coulomb excitation using a multi-isotopic Pt target and thin polarized Fe and Gd foils as ferromagnetic hosts. The experimental g -factors were found identical within errors. These and previous existing data indicate the independence of the low-lying state g -factors in even stable Pt nuclei with respect to the spin and neutron number.

The g -factor of the first 2 + states in three stable N =82 nuclei, 140 Ce, 142 Nd and 144 Sm, have been measured using the transient magnetic field technique. The levels under study were Coulomb excited with 110–116 MeV 32 S beams and spin precession after passing a thin polarized iron foil was measured. The field strength has been checked using the first 2 + state in 148 Sm as internal calibration. The obtained values were 0.97 (9), 0.84 (7), 0.76 (11) for 140 Ce, 142 Nd and 144 Sm, respectively. These remarkably lower values with respect to shell-model predictions in a proton subspace are explained in terms of neutron core excitation by quasiparticle random-phase-approximation calculations.

The elastic scattering of protons by 46Ca has been measured at seven angles for Ep = 1.82−1.90 MeV. Thirteen resonances are observed and interpreted as components of the split analogue of the 47Ca first excited state. The resonance parameters are extracted and the proton width of the IAS is determined. The partial reduced widths are fitted to the Robson one-level formula and the pertinent parameters are deduced. In addition, γ-rays from the 46Ca(p, γ)47Sc reaction were detected; the decay scheme and Γγ are deduced. The summed M1 strength for the IAS is 1.0 W.u. Hindrance of the M1 decay is explained as resulting from the polarization due to the spin-isospin interaction, which is especially strong for the analogue-to-antianalogue transitions.