## Abstract

Paramagnetic resonance has been observed at 4$\cdot $2 degrees K and a wavelength of 3$\cdot $1 cm in magnetically dilute crystals of the acetate and double magnesium nitrate of dysprosium. Values for the nuclear spins and nuclear magnetic dipole moments of the odd isotopes $^{161}$Dy and $^{163}$Dy have been deduced from the spectrum in dysprosium acetate, although the spectrum does not have axial symmetry and cannot be analyzed in detail. More reliable values for these moments have been obtained from the spectrum of dysprosium double nitrate, which has axial symmetry. It has also been possible to make an approximate calculation of the electronic ground state of dysprosium ions in this salt and estimate the nuclear electric quadrupole moments. The values of the moments are: $^{161}\mu $ = - 0$\cdot $37 $\pm $ 0$\cdot $04 n.m.; $^{163}\mu $ = + 0$\cdot $51 $\pm $ 0$\cdot $06 n.m.; and, in units of 10$^{-24}$ cm$^{2}$, $^{161}$Q = + 1$\cdot $1 $\pm $ 0$\cdot $4; $^{163}$Q = + 1$\cdot $3 $\pm $ 0$\cdot $4. For each isotope, only the relative signs of the two moments were determined experimentally; the signs quoted above are suggested as the most probable ones.