K.D. Hildenbrand

Elastic Scattering of Vector Polarized 6Li

Using the vector polarized 6Li-beam of the Heidelberg EN-Tandem1) the elastic scattering of 6Li on 12C, 16O, 28Si and 58Ni has been investigated at a bombarding energy of ELi = 22.8 MeV. The structure of the observed angular distributions of σ/σR depends in heavy ion scattering critically on E/Ecoul. Therefore the observed angular distributions of σ/σR display for 12C (E/Ecoul≈ 3.5) an oscillating pattern (fig.1) which looks like Frauenhofer diffraction scattering. The angular distribution of σ/σR for 58Ni (E/Ecoul≈ 1.4) is without any structure (fig.1) and looks like Fresnel diffraction scattering. The analyzing power had been obtained by measuring successively with a polarized and unpolarized beam (high frequency transition of the source1) on and off respectively). The polarization of the beam is known to be between 0.52 and 0.6. The lower bound is deduced from the highest up to now with this source observed asymmetry in the 6Li-4He elastic scattering2). The higher bound is estimated from the source parameters itself1). The polarization was monitored after some couple of runs either with the 1H(6Li,4He)3He reaction or, in a later stage of the experiment using the elastic scattering of 6Li on 12C. Around θcm = 44.5° and ELi = 22.8 MeV a flat maximum of the asymmetry connected with a fairly high cross section had been observed (fig.1).

Four-nucleon transfer reaction induced by 10B on 12C

Abstract The four-nucleon transfer reaction induced by 10 B on 12 C has been studied above the Coulomb barrier. The population of final states of 16 O is less selective than in other four-nucleon transfer reactions induced by 6 Li, 7 Li, or 16 O. This fact as well as the structureless angular distributions can be explained by the complexity of the structure of the ground state of 10 B, which has large components with a lower degree of symmetry than the α-particle.

Angular momentum transfer in nucleon exchange scattering of heavy ions.

Abstract The elastic scattering of 16 O on 17 O has been measured at E lab = 24, 28 and 32 MeV and θ c.m. = 90° −150°. At large energy the cross section exhibits a structureless rise at backward angles which can be described consistently with the DWBA approach for the elastic transfer.

Proton transfer in quasi-elastic and deep-inelastic reactions in the systems86Kr on88Sr,90Zr and92Mo at energies close to the coulomb barrier

Reaction products corresponding to the transfer of one and several protons have been measured over a large angular range for incident energies of 380 MeV and 400 MeV in reactions of86Kr with88Sr,90Zr and92Mo. For transitions with smallQ-values (total kinetic energy loss TKEL≦10 MeV) the transfer probabilities are deduced. The magnitudes and slopes of these probabilities as function of the distance of closest approach between two nuclei are discussed. The results for single proton transfer are well described by tunneling, whereas the transfer of two and more nucleons into low lying states of the final nuclei seems to be influenced by intermediate transfer steps with larger TKEL. The data give the possibility to discuss the relation between deep-inelastic and quasi-elastic processes. The deep-inelastic data are analyzed successfully by including deformations, charge transfer and statistical fluctuations into the frictional model of Gross and Kalinowski.

Elastic neutron transfer in the scattering of 28Si on 29Si

Abstract Angular distributions of the elastic scattering of 28 Si on 29 Si have been measured at 65 and 70 MeV (Lab) with a time-of-flight spectrometer. The structure of the angular distributions is well understood by the assumption of an interference between the elastic scattering and the elastic transfer amplitude. A spectroscopic factor of S 2 = 0.43 was deduced for the 2 s 1 2 neutron in 29 Si .

Elastic neutron transfer in the scattering of Si isotopes

Abstract Angular distributions of the elastic scattering of 28 Si on 29 Si and 30 Si have been measured for incident beam energies at E = 65 and 70 MeV with a time-of-flight spectrometer for heavy ions. At 70 MeV the neutron transfer 30 Si( 28 Si, 29 Si) 29 Si was observed in addition to the elastic channel. The pronounced oscillations in the elastic scattering distributions are interpreted as being due to an elastic transfer of neutrons between the colliding nuclei during the scattering process. This assumption is in accordance with some general features of the data and allows for the extraction of spectroscopic factors of the transferred neutrons.

Elastic scattering of 12C on 13C at the Coulomb barrier

Abstract The elastic scattering of 12 C on 13 C has been measured between c.m. energies of 4.8 and 9.5 MeV in steps of 48 keV at θ c.m. = 90°. The absence of resonance-like structures comparable to those observed in 12 C- 12 C scattering is discussed with respect to the influence of the elastic neutron transfer. The presence of this transfer even below the barrier is demonstrated by the measurement of an angular distribution of the 12 C- 13 C scattering at E c.m. = 5.76 MeV.

Interfering proton and neutron transfer in the reaction 13C(15N, 14N)14C

Abstract The reaction 13C(15N, 14N)14C leading to the ground state and first excited state in 14N has been measured at incident energies of 30, 32 and 45 MeV. For the isomultiplet channel the data are symmetric about θ = 1 2 π as predicted by the “Barshay-Temmer” theorem. The angular distributions for both exit channels show a minimum at θ = 1 2 π . The angular distributions of the transition to the ground state of 14N are nearly symmetric. The slight asymmetry can be explained with a model of two interfering transfer reactions. Recoil effects do not give rise to significant changes in the shapes of the angular distributions.

The Source for Polarized 6-Lithium Ions at the Heidelberg En-Tandem

The source was developed at the University of Hamburgl,2,3) and installed at the Heidelberg EN-Tandem4). The principle is that of an atomic beam source, but the usually used electron bombardement ionizer is replaced by a surface ionizier with an efficiency close to one. The outline of the source is displayed in fig.1. An intense atomic beam is formed by evaporating 6Li from an oven through a Laval nozzle (0.5 mm o). After that the core of the beam is skimmed by a conical and a plane heated orifice (1 and 1.5 mm o respectively). The beam is polarized with respect to the elctron spin by passing a permanent 6-pole magnet. Than it enters a weak field transition. The transition unit, which had an efficiency of 90% 4) has been redesigned in some parts and reaches now full efficiency. The surface ionizer consists of a 10×25 mm2, 0.1 thick tungsten strip heated to about 1000° C. A monolayer of oxygen which increases the work function of tungsten to values higher than the ionization energy of lithium5) is provided by an oxygen leak near the tungsten strip. In this way a nearly 100% efficiency of the ionizer is achieved. Since the surface absorption time is known to be 20 to 100 ms for temperatures around 1000°C 6) a strong magnetic field (B/B c=4) has to be provided for the ionization region in order to avoid depolarization effects and to define the direction of polarization.