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

Abstract

Polarized ll6In nuclei have been produced by capture of polarized thermal neutrons in several In compounds. At temperatures T below 77 ~ and magnetic field strengths H o of several kOe, asymmetries of a few percent of the t-decay of the II6In ground state could be observed in polycrystalline In_P, InAs and InSb, thus indicating the nuclear polarization. Nuclear magnetic resonance signals have been measured with the result for the magnetic moment ai(l16In)=2,7723 (10)nm (uncorrected). t-decay asymmetry and spin lattice relaxation time T 1 have been studied as a function of H 0 and T. The effect of H 0 is to decouple the hyperfine interaction caused by the capture-7 recoil process. However, H 0 has no influence upon T 1, which demonstrates the absence of nuclear relaxation due to paramaguetic impurities. T 1 is determined by quadrupolar relaxation. A quadrupole moment Q (116In)= 0.09 (2) b was calculated by comparison of the a16In relaxation rates with those of the stable 11Sin isotope in the same compounds. Above 30 ~ the temperature dependence of lIT 1 agrees with a recent theoretical investigation. Below 30 ~ the relaxation rate shows an anomalous behaviour, which can be explained by resonance modes due to recoil lattice defects.

Spin-polarization of radioactive 123Ing.s. by the tilted-foil method

“…In the present experiment, the nuclear polarization primarily induced by the TF method could be as large as the expected values of 9%. However, the measured nuclear polarization in ionic InAs crystal, which was reported as a good catcher material to preserve the nuclear polarization of indium isotopes [13], would be about a factor of 5 smaller than the primarily induced polarization. The same spin-relaxation may occur in the implantation into the InAs crystal, but…”

“…The expected spin-lattice relaxation time T 1 of 123 In at T ∼ 20 K is about 27 s from the 116 In case [13], which is much longer than the lifetime of the radioactive isotope 123 In.…”

“…has been measured by laser spectroscopy [10] and hence the RF frequency of β-NMR is known. Third, the catcher material (semiconducting indium) to preserve the nuclear polarization during the lifetime was investigated previously by β-NMR of 116 In [13]. Therefore, we could focus our attention on the nuclear polarization by the TF method.…”

“…Therefore, the nuclear polarization was destroyed by applying a weak B 1 of amplitude ∼ 0.3 mT. The applied RF frequency ν 0 ± Δν Q = 4649 ± 200 kHz corresponding to the Larmor frequency ν 0 and the resonance width 2Δν Q were estimated from the NMR linewidth of the 116 In in InAs crystal [13] ] ∼ 84. The duration of the RF sweep from ν 0 − Δν Q to ν 0 + Δν Q was 20 ms.…”

“…In addition, the relaxation time of the polarization in the InAs crystal might not be as long as the value in the present case suggested by ref. [13] because of the different implantation sites in the InAs crystal from the experiment in ref. [13].…”