[en] It is found that neutron pick-up cross sections up to 50 MeV excitation energy in ¹¹⁵Sn and ²⁰⁷Pb may account for the total sum rule strength of all inner shells. The ¹¹⁵Sn spectrum exhibits much more pronounced structure than that for ²⁰⁷Pb; in particular the results give first evidence for a concentration of the 1fsub(7/2) strength in a bump centered around 15 MeV. No indication for the predicted strong concentration of the 1gsub(9/2) strength in ²⁰⁷Pb is found

[en] The production of H₃⁺ ions resulting from single collisions of mass-selected ionic hydrogen clusters, H_n⁺ (n=9,25,31), with helium at high velocity (1.55 times the Bohr velocity) has been studied. A strong double H₃⁺ ion production resulting from one incident cluster is observed. Moreover, evidence for a triple H₃⁺ fragment production is presented for n=25 and 31. Thus, in this energy range, the collision gives rise to multifragmentation processes. The formation of H₃⁺ ions takes place in the fragmentation of the multicharged cluster resulting from the collision. (authors)

[en] The (³He,α) reaction on ¹²C, ¹⁶O, ²⁸Si, ⁵⁸Ni, ⁹⁰Zr, ¹¹⁸Sn, ¹²⁴Sn and ²⁰⁸Pb target was studied at 217 MeV (or 205 MeV) in order to investigate the reaction mechanism at high energy and large momentum transfer. The reaction yields large cross sections at very forward angles and strongly enhances the largest orbital momentum transfers. The main mechanism is direct pick-up although two-step processes are quite important for some transitions. The choice of the optical potential is of critical importance to reproduce the shapes of pick-up angular distributions in the framework of the DWBA-ZR analysis

[en] The excitation energy spectra of the residual nucleus ²⁰⁷Tl have been investigated up to 14 MeV using the (d,³He) reaction at 108 MeV. New groups and high lying structures are first observed up to 8.3 MeV, in addition to the five known low lying levels. Beyond a minimum at 7.13 MeV, weaker structures are observed riding over an asymetric bump located around 9 MeV. DWBA analysis of angular distributions have allowed l attributions and the determination of valence and inner hole spectroscopic factors. It is found that the valence levels at 1.33 MeV, 1.67 MeV and 3.47 MeV exhaust respectively about 65%, 60% and 45% of the 1hsub(11/2), 2dsub(5/2) and 1gsub(7/2) sum rules. The missing strengths are found below 8.3 MeV. The 2dsub(5/2) and 1gsub(7/2) holes contribute mainly to some well concentrated groups, whereas the 1hsub(11/2) strength is distributed more smoothly. Small contributions of 1gsub(9/2) and 2p strengths are tentatively identified below 7.13 MeV. The highest lying energy region up to 14 MeV may approximately account for the 1gsub(9/2) and (1fsub(5/2)) total sum-rule and about 70% of the 2p strength. The 1gsub(9/2) strength gives the largest contribution to the asymetric bump around 9 MeV. The deduced experimental strength functions are compared with theoretical calculations

[en] Strong transitions to high spin states are observed in the study of the (α,d) reaction at 218 MeV on closed shell heavy nuclei. It is shown that the highest spin valence valence n-p strength in the residual nuclei /sup 92/Nb, /sup 122/Sb, /sup 146/Eu, and /sup 210/Bi is shared between a first strongly excited fragment and higher lying groups. The valence plus outer shell (ν/sub 13/2/ x πh/sub 11/2/)/sub 12/^- strength is tentatively identified in /sup 122/Sb

No abstract available

[en] The stripping reaction (α, ³He) at 183 MeV incident energy has been used to study the neutron-particle response function on ²⁰⁸Pb target nucleus up to 15 MeV excitation energy. Detailed spectroscopic information has been obtained on the low-lying neutron states (0-4 MeV) through angular distribution measurements and standard distorted wave Born approximation analysis. A large enhancement of cross section is observed between 5 and 15 MeV. It appears as a broad bump superimposed on a continuous background which has been analysed within the framework of the plane wave break-up model. The excitation energies, angular distributions and strengths of these high-lying transitions suggest that they arise from neutron stripping to high-spin outer subshells, i.e. 2h_11/2, 1k_17/2 and 1j_13/2 in ²⁰⁹Pb. The results are compared with predictions from the core-particle model and from the quasiparticle-phonon model

[en] Fragmentation of mass-selected 60-keV/amu-H_n⁺ induced by single collision with helium has been studied for various cluster sizes n (9, 13,21, 25, and 31). The absolute cross sections of the charged fragments H_p⁺ are measured from p equal to n-2. The deduced mass distributions are strongly different from those obtained at lower collision energy (where molecular evaporation is mainly involved) due to a strong production of ionic fragments with a size of p/n<=0.5. Moreover, the distributions for p/n< =0.5 are found to have scaling properties and to follow a power law A^-τ, where A is the normalized fragment mass (p/n) and τ an exponent close to 2.6. (authors)

[en] The energy spectra of residual ¹¹¹Sn, ¹¹⁵Sn, ¹¹⁹Sn nuclei have been studied with 38 keV resolution, up to excitation energies of the order of 16 MeV, using the (³He,α) reaction at 39 MeV. Complete angular distributions have been obtained for the ¹¹⁶Sn(³He,α)¹¹⁵Sn reaction; two angles were measured for the other isotopes. Several new levels or groups are observed up to approximately 3.5 MeV in the three isotopes, due to the momentum matching conditions. Spectroscopic factors are determined for all observed levels up to 3.71 MeV in ¹¹⁵Sn and for the low-lying strongly populated levels with known Jsup(π) in ¹¹¹Sn, ¹¹⁹Sn. The fragmentation of the l=4, 5 valence hole strengths and the excitation of levels with anomalous spins and parities in the intermediate energy region in ¹¹⁵Sn are discussed in terms of weak coupling and two step coupled channels calculations. The fine structure previously reported for the 1g(9/2) hole orbital in ¹¹⁵Sn is clearly confirmed and enhanced in the present experiment. The fragmentation of this orbital is observed for the first time in ¹¹¹Sn, between 3.4 and 5.2 MeV and in ¹¹⁹Sn, though to a lesser extent, between 3.8 and 6.5 MeV. In the fine structure region the 1g(9/2) hole strength is found to decrease from 62% to 43% and 28% in respectively ¹¹¹Sn, ¹¹⁵Sn and ¹¹⁹Sn; theoretical calculations do not explain these experimental strengths and fragmentations. The first 9/2⁺, 1/2^-, 3/2^- IAS are identified in ¹¹¹Sn. Previously unreported, weakly populated IAS are also found in ¹¹⁵Sn and ¹¹⁹Sn. The energies and widths are measured. The spectroscopic factors and isospin splitting of these states are discussed in the framework of the Lane coupled channels formalism for the neutron form factor

[en] The excitation energy spectra of the residual nucleus ²⁰⁷Tl have been investigated up to 14 MeV using the (d, ³He) reaction at 108 MeV. New high-lying states are observed for the first time up to 8.3 MeV, in addition to the five known low-lying levels. Beyond 7.13 MeV excitation energy, weaker structures are observed riding over a wide asymmetric bump. DWBA analysis of the angular distributions has allowed l attributions and the determination of valence and inner-hole spectroscopic factors. The deduced experimental strength functions are compared with theoretical calculations. (author)