Abstract
The magnetic relaxation of dilute Sm spins in Pr ethylsulphate has been measured by electron spin echoes. The Sm spins are relaxed by the fluctuating magnetic fields of the Pr spins which form XY chains. The measurements are in satisfactory agreement with the relaxation function calculated using the known spin correlation fractions for the XY model. As predicted for the XY model, spin diffusion is found to be absent or negligible.