Interaction of 17F with a 208Pb target below the Coulomb barrier

The interaction of loosely bound (S _p = 600 keV) ¹⁷F ions with a ²⁰⁸Pb target was studied at E _lab = 86 MeV, below the Coulomb barrier, by measuring the differential cross-section for the quasi-elastic scattering and the cross-section for the exclusive breakup process ¹⁷F $ \rightarrow$ ¹⁶O + p . The small reaction and exclusive breakup cross-sections confirm the small reactivity of this system, even at low energy, and indicates that the ¹⁷F small binding energy plays a minor role in the reaction dynamics.     

Elastic scattering for the system 11Be + 209Bi at Coulomb barrier energies

The elastic scattering process for ¹¹Be ions impinging on a ²⁰⁹Bi target was studied in the energy range around the Coulomb barrier. The angular distributions of the ¹¹Be scattered particles were analyzed within the optical model framework in order to evaluate the reaction cross section, which turned out to be much larger than the fusion one, especially in the sub-barrier region. The comparison with the system ⁹Be + ²⁰⁹Bi showed that the reaction cross section is larger for the reaction ¹¹Be + ²⁰⁹Bi in the energy range around the Coulomb barrier, while they are rather similar at higher bombarding energies. This result suggests that direct processes related to the ¹¹Be halo structure and lower binding energy are more relevant at near-barrier energies.     

Preparation and characterization of strontium targets for nuclear astrophysics experiments

Journal of Radioanalytical and Nuclear Chemistry - The present paper describes preparation and characterization of strontium targets for nuclear astrophysical experiments with alpha particles...     

Low-spin excitations in 146Sm

The low-spin excitations of the nucleus ¹⁴⁶Sm which is just two neutrons and two protons away from the N = 82 shell and Z = 64 subshell closures have been investigated by means of the ¹⁴³Nd (??, n) and ¹⁴⁴Nd (??, 2n) fusion-evaporation reactions. We established 47 hitherto unknown energy levels up to 4.7MeV and 75 new transitions. In addition, 7 spin assignments were possible from the ??-?? angular correlation analysis. The structure of the possible candidates for a 2⁺ ? 3^? quadrupole-octupole multiplet are first discussed in terms of the harmonic vibrational model. A comparison of these states with the corresponding ones in the neighboring N = 84 isotones is also presented. Finally, the structure of the ¹⁴⁶Sm nucleus is interpreted in terms of the IBA-spdf model. It is shown that the model is able to reproduce the experimental relative transition strengths of the 2⁺ ? 3^? quadrupole-octupole multiplet and also a series of collective properties such as the proposed double-octupole excitations.     

Isomerism of low-lying states in 86Y

Low-energy isomeric states of ⁸⁶Y were populated in the reaction ⁷³Ge + ¹⁶O at 57MeV and were investigated by means of delayed n $ \gamma$ and $ \gamma$ $ \gamma$ coincidences. A half-life of 70(7)ns was measured for the 5^- state at 208keV, yielding an exceptionally small B(M1) value of 2.0(7)×10^-5 W.u. and a B(E2) value of 0.34(⁺²⁴ _-13) W.u. For the other three known isomeric states at 218, 243, and 302keV, the half-lives extracted from the present experimental data are in very good agreement with previous measurements. Given the newly observed isomeric character of the 5^- 208keV state, the re-analysis of earlier experimental data on the 302keV isomer led to a new spin-parity assignment, 6⁺, for this state. In addition, this re-evaluation provided two g -factors, -0.083(3) and +0.63(2) , for the 208 and 302keV states, respectively. The results are discussed in terms of spherical-shell model calculations performed with a truncated space of configurations built on the f _5/2 , p _3/2 , p _1/2 , and g _9/2 valence orbitals. Effective spin, orbital, and “tensor” g -factors were determined empirically for protons and neutrons in the considered configuration space.     

Partial fusion of a weakly bound projectile with heavy target at energies above the Coulomb barrier

Partial-fusion cross-sections for the systems ⁶Li + ²⁰⁸Pb, ⁹Be + ²⁰⁹Bi have been determined. The effect of breakup on fusion for weakly bound projectiles ⁶Li and ⁹Be incident on ²⁰⁸Pb or ²⁰⁹Bi targets has been discussed comparing experimental fusion cross-section excitation functions to those evaluated with a semi-classical approach. It is shown that complete fusion of a weakly bound projectile with heavy target is reduced, whereas the breakup process has very little influence on the total-fusion cross-section for some of the studied systems at energies above the Coulomb barrier.     

Quasi-elastic backscattering of 6,7Li on light, medium and heavy targets at near- and sub-barrier energies

High-spin states in the nucleus ⁷²Ge were investigated via the ⁷⁰Zn( $ \alpha$ , 2n)⁷²Ge reaction at a beam energy of 30MeV, using the AFRODITE spectrometer. One aim of the study was to search for tetrahedral states. There was no evidence for such states in our coincidence data. The existing decay scheme was substantially revised and extended. Several $ \gamma$ -ray placements and level spin-parities were changed, and some 30 new transitions were added to the level scheme. One new negative-parity rotational band was identified. The new band is likely the unfavoured signature partner of the band built on the previously known $\ensuremath I^{\pi}=3^{-}$ state at 2515keV. The two negative-parity bands are interpreted as involving an aligned octupole vibration which evolves to a four-quasiparticle structure at higher spins. The upbend in the yrast band is interpreted as the AB neutron alignment. The band structures are discussed with reference to Cranked Shell Model calculations, the aligned angular momenta, experimental routhians, and moments of inertia.     

Scattering of 11Be halo nucleus from 209Bi at the Coulomb barrier

The scattering of the radioactive, weakly bound, halo nucleus ¹¹Be from ²⁰⁹Bi has been studied at 40MeV beam energy. The measurement performed with a low-intensity and a large-emittance secondary beam could be made using an extremely compact, large solid angle (∼ 2π sr) detecting set-up, based on 8 highly segmented Si telescopes. The ^{11, 9}Be scattering angular distributions, as well as their relative reaction cross-sections, resulted to be rather similar. This may suggest that at Coulomb barrier energies the halo structure and the very small binding energy of the ¹¹Be projectile have no big influence on the reaction dynamics.