jDependence of the (F19,

Abstract

The shapes of the observed angular distributions for the reactions 2 8.so si (i9 F> 16Q)3I,33 P to | + and f + states differ strongly. A consistent description of this j dependence and of the ground-state i + angular distributions is given by distorted-wave Born-approximation calculations which assume triton cluster transfer and include spin-orbit potentials in both entrance and exit channels. We find from coupled-channel Born-approximation calculations that inelastic excitation of 19 F does not affect the shapes significantly.Rather little is known about spin-dependent terms in the heavy-ion optical potential, although recent work 1 with a polarized 6 Li beam has shown the need for a spin-orbit 1 • s term. Transfer reactions in principle should be sensitive to spindependent forces. However, when using heavy ions, one is concerned with the transfer of a particle from an (Z 2 , j 2 ) orbital in the projectile to an (^uii) orbital in the residual nucleus. The angular momentum selection rules for a one-step process usually then allow several values of the transferred angular momentum L, and these can differ according to whether the angular momentum transferred to the target nucleus, j ly is l x +i or Z 1 -|. This difference in L gives rise to a strong j 1 dependence even in the absence of spin-dependent potentials. 2 In the present work we choose a case where Z 2 = 0 so that L-l 1 uniquely and the dependence of the angular distribution on j 1 for a given L can be observed.Specifically we have studied the reactions 2 a,30 Si (i9 F? i6 O) 3i,33p a t£ lab = 60 MeV. We assume that these reactions transfer a tritonlike cluster of three particles in a relative Os state, thereby preserving the simplicity of a one-particle transfer process. This assumption should be well justified for the ( 16 Ol 19 F) overlap since 92% of the 19 F wave function can be expressed 3 ' 4 in terms of a cluster moving with angular momentum Z 2 = 0 with respect to the le O core. The (SiIP) overlap presumably involves a number of components, however the relative Os cluster should dominate the reaction since (1) this allows the cm. wave function to extend as far out as possible which is important for surface reactions and (2) this does not require rearrangement of the three particles during the transfer process. Since l 2 = 0 with the cluster assumption, we have, as remarked, L-l x uniquely. Furthermore, since the target spin is zero, the spin of the residual nucleus is j^. Thus we can compare L = 2 transfer to the lowest f + and | + states of 31 P and 33 P; we also study L = 0 transfer to the | + ground states.The experiments were carried out with a 60-MeV 19 F 6+ beam from the MP tandem van de Graaff accelerator of the University of Minnesota using a sputter-type ion source and Freon as source gas. Beam currents of 300-500 nA of 19 F(6 + ) were used to bombard isotopically enriched Si0 2 targets (about 50 jug/cm 2 ), which had a carbon backing (about 5 jug/cm 2 ). The targets were continuously rotated while in the beam to reduce target deteriorat...

Spin alignment and polarisation in the (16O,15N) transfer reactions

“…These measurements are usually done using the angular correlation method, where the 7-ray distribution is measured [4] or for states unstable to particle decay with the measurement of particle correlation functions [5]. The increased interest in spin dependent effects in heavy ion reactions is due to the observation of anomalous angular distributions for single and mul-* Also Fachbereich Physik, Freie Universit~it Berlin tinucleon transfer [3,6]; it is also evident that with increasing incident energy and increasing angular momenta the importance of spin-orbit effects in heavy ion reactions must become obvious. This circumstance is emphasized by the fact that large degrees of polarisation are expected in many heavy ion reactions at appropriate Q-values (mainly negative) due to the semiclassical properties of the reaction mechanism.…”