Application of Polarized Deuterons in (d, pγ) Angular Correlation Measurements

Abstract

The application and use of tensor polarized beams of deuterons in (d,py) angular correlation experiments with spin-0 targets is described in connection with the measurement of mixing ratios of decays from spin-f states in 13 C and 31 Si.The angular distribution of y rays emitted from an excited nuclear level populated in a nuclear reaction is a function of the initial and final level spins, the multipole mixing ratio for the y-ray transition, and the population ratios for the magnetic substates of the initial state. These population ratios are not, in general, accurately predicted by reaction theories, and for this reason the technique 1 of detecting the outgoing particle along the direction of the beam axis has been widely used as a reaction-mechanism-independent method of extracting spectroscopic information from angular correlation experiments. In this collinear geometry, the maximum substate populated in the residual nucleus is limited to a value equal to the sum of the intrinsic spins of the incident particle, target, and emitted particle. A reaction such as ( 3 He, a) on spin-0 targets then populates only lral = i substates [P(|) = l], and there is no unknown population ratio. On the other hand, the (d, p) reaction on spin-0 targets populates both \m\-\ and f substates, and the mixing ratio x can be extracted only if the experimental angular correlation provides enough information to determine both x and the unknown population parameter, P(-|)/P(-|). This requirement is not always fulfilled and has often limited the usefulness of (d, py) angular correlation measurements in the past, especially in studies of decays from spin-J-states.The present work describes the utilization of tensor polarized deuteron beams in measuring (d,py) angular correlations with spin-0 targets and illustrates the first application of a slight variation of a method proposed by McCullen and Seyler 2 for circumventing the difficulty associated with the unknown population parameter. The technique requires measuring correlations at different known values of the beam polarization, and then forming a combination of the correlations which is not dependent on the population of the \m\ = j substates in the residual nucleus. The method, as described below, was tested in a measurement of the mixing ratio of the 3.68 -0.0 (|" -* \") transition in 13 C. We have obtained a mixing ratio of -0.154 ±0.054, in agreement with a previous value of -0.096tjJ;[J;jJ obtained by Poletti, Olness, and Warburton from y-y correlation studies. 3 The method is applied here to a measurement of the unknown mixing ratios of the 2.32-0.0 (f + -f + ) and the 3.54-0.76 (f~-~i + ) transitions in 31 Si.The experiments consisted of angular correlation studies of the reaction 30 Si(d/>y) 31 Si initiated by ~15-nA beams of polarized deuterons from the Triangle Universities Nuclear Laboratory Lamb-shift, polarized ion source. 4 The protons were detected at ~180° in a 500-/im silicon surface-barrier detector and the coincident y rays were detected at angles between 25° and 90...