Abstract
An unexpected ordered state among Pr nuclei in the Van Vleck paramagnet PrBi is inferred from a sharp increase in specific heat at 10 mK as well as from the onset of strong irreversible heating when sweeping the field at these temperatures. Several possible explanations are discussed, among which the coupling between the nuclei via hyperfine interaction (within the ions) and exchange interaction (between the ions) is likely to be the true ordering mechanism.