The second order recombination and spin-exchange relaxation of atomic deuterium at low temperatures in a low magnetic field

Abstract

We measured the 2nd order recombination rates and spin-exchange relaxation of atomic deuterium (D) in a4He coated sample cell, using the hyperfine resonance of β(F = 1/2, mF= −1/2) − δ(F = 3/2, mF= −1/2) transition in a low magnetic field (3.9 mT) at temperatures between 0.6 K and 1.2 K. At lower temperatures below 0.9 K, the density decay of D atoms was dominated by D-D recombination on the liquid He surface. We found that the surface recombination cross length was 1DD= (5.5 ± 1.3) × 10−9cm and the adsorption energy of D on4He surface was ea= 3.97 ± 0.07 K. Compared with prior measurements at high magnetic fields by other groups, 1DDat low field was orders of magnitude smaller than what was expected when the scaling of 1/B2dependence of the direct recombination mechanism was used, and in addition, eawas significantly larger. This was attributed to the onset of the resonant recombination mechanism for the D-D surface recombination at high fields. Above 0.9 K, D-D volume recombination and recombination of D with hydrogen impurity became dominant processes of the density decay of D. The transverse relaxation times were measured and we determined the D-D spin-exchange relaxation rates, GDD= (1.4 ± 0.6) × 10−10cm3sec−1. It was smaller than theoretical calculations.