Reorientation of Aligned Nuclei

Abstract

Where nuclei aligned at low temperatures decay by a two-stage cascade, the degree of alignment of the intermediate state may be influenced by magnetic coupling. If the second stage is $\gamma$ radiation, the angular distribution will be influenced as a consequence. This effect is treated by assuming a static interaction and twofold ionic degeneracy. In particular for high temperatures very explicit results are given for ${\Delta }^{\prime }$, the mean degree of alignment of the intermediate state. This is dependent primarily on the mean life and magnetic moment of the intermediate state. If is found that if the properties of the intermediate state are similar to those of the initial state. (1) Reorientation effects will be present if $\tau >{10}^{-9\mathrm{}}$ sec; (2) They may either increase or decrease ${\Delta }^{\prime }$; (3) A strong external field cancels the effect altogether; (4) Reorientation can introduce ${cos}^4\theta$ terms into the angular distribution even at the highest temperatures; (5) Where $\tau$ is very long, ${\Delta }^{\prime }$ tends to a finite limit. The calculations are applied to an experiment.