The energy spectra of photons following negative muon absorption in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$, and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ have been measured with two NaI spectrometers. The branching ratios for the emission of high energy photons give information on the induced pseudoscalar coupling constant $g_P$ in nuclear matter. The data for light nuclei are in agreement with the theoretical calculations using the nucleonic value of $g_P$≊7$g_A$ predicted by the partially conserved axial vector current hypothesis, while significantly lower values of $g_P$ are required to fit the data of the heavier elements with presently existing theoretical predictions. Disregarding the remaining theoretical uncertainties, these results can be interpreted as a further indication of the renormalization of the nucleonic form factors inside the nucleus.

• Received 26 October 1987

DOI:https://doi.org/10.1103/PhysRevC.37.1633