Relaxation phenomena and nuclear magnetic resonance of116In(T 1/2=14s) produced by capture of polarized neutrons in the indium III–V compounds

Abstract

Polarized116In nuclei have been produced by capture of polarized thermal neutrons in several In compounds. At temperaturesT below 77 °K and magnetic field strengthsH 0 of several kOe, asymmetries of a few percent of the β− decay of the116In ground state could be observed in polycrystalline InP, InAs and InSb, thus indicating the nuclear polarization. Nuclear magnetic resonance signals have been measured with the result for the magnetic moment μ i (116In)=2.7723 (10) nm (uncorrected). β− decay asymmetry and spin lattice relaxation timeT 1 have been studied as a function ofH 0 andT. The effect ofH 0 is to decouple the hyperfine interaction caused by the capture-γ recoil process. However,H 0 has no influence uponT 1, which demonstrates the absence of nuclear relaxation due to paramagnetic impurities.T 1 is determined by quadrupolar relaxation. A quadrupole momentQ(116In)=0.09 (2) b was calculated by comparison of the116In relaxation rates with those of the stable115In isotope in the same compounds. Above 30 °K the temperature dependence of 1/T 1 agrees with a recent theoretical investigation. Below 30 °K the relaxation rate shows an anomalous behaviour, which can be explained by resonance modes due to recoil lattice defects.