A. Gamp

Fission characteristics of the composite system 32S + 50Ti: (II). Energy and angular dependence

Abstract Angular distributions, mass distributions and excitation functions have been measured for the heavy fragments 35 ≦ A ≦ 60 produced in the bombardment of 50 Ti by 32 S at beam energies between 121 and 166 MeV. The angular distributions are of the form ( sinθ ) −1 for all masses, although slight deviations do occur. The mass distributions exhibit a striking energy dependence with a strong trend towards symmetric mass divisions at high energies. The excitation functions agree qualitatively with the predictions of the rotating liquid drop model.

Fission characteristics of the composite system 32S+50Ti: (I). Correlations between coincident fragments

Abstract The characteristics of “fission-like” processes observed in the bombardment of 50 Ti with 32 S ions of 140 MeV energy are investigated in a coincidence experiment between a time-of-flight telescope and a position sensitive ΔE - E ionization chamber. Coincident particles were identified and their energy and angular correlations in and normal to the reaction plane were measured. The experiment proves the binary nature of the mass division. Both the width and the average value of the total kinetic energy distribution are consistent with the values extrapolated from fission of heavier nuclei. An average number of 3±1 nucleons are emitted during the reaction; α-particle emission is not an important decay mode.

High energy structures in heavy ion collisions: A multi-phonon description

Energy spectra of fragments from the36Ar+208Pb reaction at 11 MeV/n exhibit structures at high excitation energies. These structures are interpreted in terms of target multi-phonon excitations built from giant resonances. The importance of such processes for the kinetic energy dissipation in heavy ion collisions is emphasized.

The Heidelberg 3MV-CW Heavy Ion Postaccelerator Section Using Independently Phased Spiral Resonators

The Heidelberg 3MV heavy ion postaccelerator section based on independently phased normal conducting spiral resonators working at 108 MHz is described. The design veloctity of the spiral resonators is ß = 0.10. The peak voltage drop is 0.37 MV at 20 kW CW input power (0.74 MV at 80 kW, duty factor 0.25) corresponding to a peak accelerating field of 1.7MV/m (3,4MV/m) averaged over the external length of the resonator. Using a synchronous phase of ¿S = -20° gives a maximum effective voltage of 0.35 MV (0.7 MV). The resonators are stacked in modules of four with one external quadrupole doublet. The total effective voltage of this first test section of the Heidelberg postaccelerator under construction is 3 MV-CW (6 MV d. f. 0,25) providing ion energies up to 6 MeV/ nucleon at mass A=40. The postaccelerator will be integrated into the existing experimental area. Beam matching to the longitudinal acceptance of the postaccelerator is done by a separate spiral resonator as rebuncher. The high quality of the tandem beam with respect to longitudinal and transverse phase space is maintained in the designed postaccelerator.

Nucleon exchange in scattering of carbon isotopes

Abstract The elastic scattering of 12 C on 13 C and 14 C, of 13 C on 14 C has been measured in the vicinity of the Coulomb barrier. The structure of the angular distributions is consistently described using the method of molecular wave functions which takes into account the exchange of the valence particles.

High excitation energy structures in208Pb

Inelastic spectra from the36Ar+208Pb reaction at 11 MeV/n and20Ne+208Pb at 30 MeV/n have been measured with a time of flight spectrometer. Structures ranging up to 100 MeV excitation energy are observed together with previously known giant resonance excitations. Transfer-evaporation reactions are shown to contribute only to the background under the structures. These structures are interpreted in terms of an excitation of the target nucleus through a direct process.

Structures in the excitation functions for compound reactions in the12C+14C system

Excitation functions for the elastic scattering of12C on14C and the reactions14C(12C, α)22Ne,14C(12C,t)23Na and14C(12C,d)24Na have been measured in the vicinity of the Coulombbarrier. Strong fluctuations of the differential cross sections as a function of incident energy are observed in the α-particle, triton and deuteron channels. The total yield in the three different channels shows correlated structures at energiesEc.m.=6.8, 7.2 and 8.3 MeV. This phenomenon is similar to the structures observed in the12C+12C reactions and indicates the possible presence of resonances in the entrance channel.

Elastic scattering of15N on19F,19F on18O and19F on16O at low energies and elastic transfer

Angular distributions of the elastic scattering in the range of 30–160 ° θcm have been measured for the systems15N+19F,19F+16O and19F+18O at three energies, the highest being approximately 4 MeV above the Coulomb barrier. The large differences observed in the structure of the angular distributions at large angles are discussed considering elastic transfer, and the angular momentum balance for the possible direct surface reactions. The analysis yields a consistent description of the data in terms of elastic transfer.

Pairing effects in quasi-elastic neutron transfer between Tin isotopes

The transfer of neutrons between low-lying states of Tin isotopes has been measured in the reaction120Sn→112Sn at energies below the Coulomb barrier. The transfer probabilities are deduced as function of the classical minimum distance from transfer and scattering cross sections at different angles and two energies. At the smallest distances very large transfer probabilities,pt=0.5, are observed for one- and two-neutron transfer. The two-neutron transfer is significantly enhanced as compared to a successive independent single-nucleon transfer. The definition of enhancement is discussed.

Evaporation residue cross sections from the fusion of52Cr+110Pd

Evaporation residue cross sections for the fusion of52Cr and110Pd were studied at four energies close to the barrier (up toECM−EB=26 MeV). The cross sections were analysed using a multiple-chance fission/evaporation calculation. Agreement with the data is obtained with a fission barrier reduced by 40 to 20%, depending on incident energy.