Nuclear Quadrupole Absorption in Indium Metal

The nuclear quadrupole resonance spectrum of indium metal has been observed and studied over the temperature range 4^∘{}K to 225^∘{}K. The four transition frequencies occur in ratios of 1:2:3:4, as expected from the crystal structure of indium. The lowest transition at 1.881 Mc (at 4.2^∘{}K) gives a quadrupole coupling constant of (45.19±{}0.02) Mc.The root second moment of 18 kc is substantially greater than the 4 kc predicted from magnetic dipolar coupling among the nuclei, is temperature independent, but is somewhat sample dependent. It is shown that for a pure quadrupole resonance, the pseudo-exchange coupling produces an exchange broadening. This mechanism is shown to contribute about 10 kc to the root second moment and predicts a Gaussian line shape, as observed. It is concluded that in some cases magnetic impurities must be present, but it is not known whether or not the narrowest line represents a natural width.The field gradient is computed assuming point ions and a uniform electron density by a technique that converges rapidly with distance, but the answer is too small by a factor of 3. It is argued that it is important to consider the p valence electrons. The temperature dependence of frequency is very strong (a 23% decrease between 4^∘{}K and 220^∘{}K), and unexplained. It appears to show that the field gradients cannot be computed assuming point ions and a smooth charge distribution.A resonance in the superconducting state is reported.