The energy shifts of the nuclear gamma rays from the first rotational states of ${\mathrm{Nd}}^{150}$, ${\mathrm{Sm}}^{152}$, ${\mathrm{Gd}}^{154}$, ${\mathrm{Er}}^{166}$, ${\mathrm{W}}^{182}$, ${\mathrm{W}}^{184}$, and ${\mathrm{W}}^{186}$ due to the presence of a muon in a $1s$ state have been measured. The shifts are related to changes in the nuclear mean-square charge radius, and are compared with Mössbauer isomer-effect measurements.

• Received 10 June 1968

DOI:https://doi.org/10.1103/PhysRevLett.21.457