Reactions induced by radioactive {sup 6,8}He beams from the SPIRAL facility were studied on {sup 63,65}Cu and {sup 188,190,192}Os targets and compared to reactions with the stable {sup 4}He ...projectiles from the Mumbai Pelletron. Partial residue cross sections for fusion and neutron transfer obtained from the measured intensities of characteristic in-beam {gamma} rays for the {sup 6}He+{sup 63,65}Cu systems are presented. Coincidence measurements of heavy reaction products, identified by their characteristic {gamma} rays, with projectilelike charged particles, provide direct evidence for a large transfer cross section with Borromean nuclei {sup 6}He at 19.5 and 30 MeV and {sup 8}He at 27 MeV. Reaction cross sections were also obtained from measured elastic angular distributions for {sup 6,8}He+Cu systems. Cross sections for fusion and direct reactions with {sup 4,6}He beams on heavier targets of {sup 188,192}Os at 30 MeV are also presented. The present work underlines the need to distinguish between various reaction mechanisms leading to the same products before drawing conclusions about the effect of weak binding on the fusion process. The feasibility of extracting small cross sections from inclusive in-beam {gamma}-ray measurements for reaction studies near the Coulomb barrier with low intensity isotope separation on-line beams is highlighted.
Excitation functions have been measured for quasi-elastic back-scattering of
16O on
92Zr,
144Sm,
154Sm and
186W targets. A new procedure to extract representations of fusion barrier distributions is ...suggested and applied. The results are compared with barrier distributions obtained from fusion data and with coupled-channel calculations. The representations from quasi-elastic scattering are consistent with those from fusion below the average barrier energy. However, the effect of transfer smooths the quasi-elastic representations at higher energies, so that the sensitivity to the barrier distribution is reduced.
Measurements of the helium-cluster breakup and neutron removal cross-sections for neutron-rich Be isotopes 10–12,14Be are presented. These have been studied in the 30 to 42 MeV/nucleon energy range ...where reaction measurements are proposed to be sensitive to the cluster content of the ground-state wave-function. These measurements provide a comprehensive survey of the decay processes of the Be isotopes by which the valence neutrons are removed revealing the underlying α–α core-cluster structure. The measurements indicate that clustering in the Be isotopes remains important up to the drip-line nucleus 14Be and that the dominant helium-cluster structure in the neutron-rich Be isotopes corresponds to α–Xn–α.
Results from a study in inverse kinematics of the $^{24}$Ne(d, pγ)$^{25}$Ne reaction, using a radioactive beam of $^{24}$Ne from the SPIRAL facility at GANIL, are reported. First, a brief overview is ...given of several methods using radioactive beams to study the classic single-nucleon transfer reactions such as (d, p) or (d, t)/(d, $^{3}$He), where the experimental design is strongly influenced by the extreme inverse kinematics. A promising approach to deliver good energy resolution is to combine a high geometrical efficiency for kinematically complete charged particle detection with a high efficiency array for gamma-ray detection. One of the first dedicated set-ups for this type of experiment is the TIARA silicon strip array combined with the EXOGAM segmented germanium array. Together they comprise a highly compact, position-sensitive particle array with 90% of 4π coverage, mounted inside a cubic arrangement of four segmented gamma-ray detectors in very close geometry with 67% of 4π active coverage. Using this setup, the structure of $^{25}$Ne has been studied via the (d, p) reaction. A pure ISOL beam of 10$^{5}$ s$^{-1}$ of $^{24}$Ne at 10 MeV/A was provided by SPIRAL and bombarded a CD$_{2}$ target of 1 mg/cm$^{2}$. The $^{25}$Ne was detected at the focal plane of the VAMOS spectrometer where the direct beam was separated and intercepted. Reaction protons were detected in coincidence with little background. Four resolved peaks were recorded between E$_{x}$ = 0 and 4 MeV. The data confirm and extend the results from a multinucleon transfer study using the ($^{13}$C,$^{14}$O) reaction. Further information has been obtained using the energies of coincident gamma-rays. The reactions $^{24}$Ne(d, dγ)$^{24}$Ne, $^{24}$Ne(d, t)$^{23}$Ne and $^{24}$Ne(d, $^{3}$He)$^{23}$F were recorded simultaneously and analysis of these is also underway.
Fusion excitation functions for sup 144Sm + sup 16O and sup 17O have been measured to high precision. The extracted fusion barrier distributions show a double-peaked structure which is interpreted in ...terms of coupling to inelastic excitations of the target. The effect of the neutron stripping channel is evident in the reaction with sup 17O. These barrier distributions show clearly the signatures of specific inelastic and transfer channels.
The sign of the mean transverse momentum of non-equilibrium light charged particles was determined from the circular polarization of coincident
γ-rays emitted from residual nuclei for
14
N-induced ...reactions on
154
Sm at incident energies,
E/
A=35, 100 and 155 MeV. Results of the emitted
α-particles at mid-central collisions show the predicted transition from mean-field dominated dynamics at low energies to nucleon-nucleon collision dominated dynamics at high energies.
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