Multiplicities as a function of $\gamma$-ray energy have been measured for continuum $\gamma$-ray spectra produced in argon- and calcium-induced reactions. A peak sometimes occurs in the multiplicity spectrum, indicating a correlation between $\gamma$-ray energy and multiplicity (spin). This correlation can be explained by rotational motion of the nucleus, suggesting basically prolate nuclear shapes. Absence of structure in the multiplicity spectrum is interpreted to indicate noncollective motion, and hence spherical or oblate shapes.

• Received 12 December 1977

DOI:https://doi.org/10.1103/PhysRevLett.40.629