A Dynamically Polarized Deuteron Target

Abstract

A dynamically polarized deuteron target was constructed at the Triangle Universities Nuclear Laboratory for low energy polarized neutron transmission experiments. Theoretical calculations suggested a measurement of the longitudinal spin-dependent total $vec[n]-vec[d]$ cross section difference, $Deltasigma_L$, would provide evidence of three nucleon force effects.

The target was operated at a temperature of 0.5K with a recirculating $ˆ3$He evaporation refrigerator and a 2.5T split-pole superconducting magnet which can be mechanically mounted to produce either a longitudinally or tangentially polarized target relative to the beam momentum. The target material consisted of a cube of volume 2.7 ml of either partially (D6) or fully (D8) deuterated 1,2-propanediol chemically doped with EHBA-Cr$ˆV$ to provide the paramagnetic centers for dynamic nuclear polarization with microwaves in the region 69GHz. Polarization was monitored during the experiment using a continuous wave NMR Q-meter capable of both phase sensitive and magnitude detection. A PC running LabVIEW controlled data acquisition, frequency sweep of the digital frequency synthesizer and a novel background cancellation technique. A pre-recorded background signal was subtracted on a channel by channel basis before the NMR spectrum was sampled.

Polarization was extracted from the NMR spectra by a fit to a theoretical lineshape. Effects including dispersion were considered. The equal spin temperature (EST) hypothesis was used to determine deuteron polarization indirectly though the measurement of polarization of the residual protons in the partially deuterated sample. Efforts to improve the system stability and signal-to-noise are discussed along with numerical methods, fitting strategy and evaluation of uncertainties.