3d→2pPionic Transition inNi58andNi60

The $3d\to 2p$ pionic x rays in ${\mathrm{Ni}}^{58}$ and ${\mathrm{Ni}}^{60}$ have been observed in order to measure effects due to the strong interaction between the pion and the nucleus. These isotopes were chosen because nuclear effects in the x-ray energy are expected to be large and the x-ray yield is appreciable. We see a large nuclear level shift and broadening, but no isotope effect within experimental error. The level shift is found to have a strong dependence on the neutron radius, and our results are consistent with the hypothesis of equal neutron and proton rms radii. We also compute the isotope shift for the $2p\to 1s$ transition in ${\mathrm{O}}^{16}$ and ${\mathrm{O}}^{18}$ and find that experimental measurements require the neutron radius of ${\mathrm{O}}^{18}$ to be greater than the neutron radius of ${\mathrm{O}}^{16}$. However, uncertainties in the pion-nuclear interaction do not allow an accurate determination of the neutron radius.