Total cross sections for the pion single-charge-exchange reaction $^{12}\mathrm{C}$(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{0}$${)}^{12}$N (ground state) were measured at 116, 160, 180, 200, 230, and 291 MeV with a fast activation technique. The excitation function for this nonanalog, spin-flip transition was found to be flat over this energy region that includes the (3,3) resonance. Good agreement is noted between these measurements and the estimated cross sections obtained from pion inelastic scattering measurements for the analog reaction $^{12}\mathrm{C}$(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{+}$'${)}^{12}$${\mathrm{C}}^{\mathrm{*}}$ (${1}^{+}$,T=1,${\mathit{E}}_{\mathit{x}}$=15.1 MeV) for all energies except 230 MeV. Distorted-wave impulse-approximation calculations in the \ensuremath{\Delta}-hole formalism do not reproduce the trend of the data.

This paper describes an experiment designed to search for a new form of nuclear matter—a bound η‐nucleus system. The (π+,p) reaction was used to study the possible formation of an η‐mesic nucleus. No narrow η‐nuclear bound states were observed using Li, 12C, 16O and 27Al targets. The results of this experiment have now been published elsewhere by Chrien et al.

Differential cross sections for the double-isobaric-analog-state transition in the reaction /sup 48/Ca(..pi../sup +/,..pi../sup -/)/sup 48/Ti at an incident energy of 35 MeV were measured over the angular range 20/sup 0/--80/sup 0/. The cross section extrapolated to 0/sup 0/ is 3.1 +- 0.8 ..mu..b/sr, and the angular distribution shape is nearly isotropic. The results are compared to second-order optical-potential calculations and to the systematics of low-energy double-charge-exchange reactions. Measurements were also made at 50 MeV at scattering angles of 25/sup 0/ and 40/sup 0/. The analog-state transition could not be clearly observed above the background of non-analog-state transitions.

Differential cross sections for the double-isobaric-analog-state transition in the reaction $^{48}\mathrm{Ca}$(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${)}^{48}$Ti at an incident energy of 35 MeV were measured over the angular range 20\ifmmode^\circ\else\textdegree\fi{}--80\ifmmode^\circ\else\textdegree\fi{}. The cross section extrapolated to 0\ifmmode^\circ\else\textdegree\fi{} is 3.1\ifmmode\pm\else\textpm\fi{}0.8 \ensuremath{\mu}b/sr, and the angular distribution shape is nearly isotropic. The results are compared to second-order optical-potential calculations and to the systematics of low-energy double-charge-exchange reactions. Measurements were also made at 50 MeV at scattering angles of 25\ifmmode^\circ\else\textdegree\fi{} and 40\ifmmode^\circ\else\textdegree\fi{}. The analog-state transition could not be clearly observed above the background of non-analog-state transitions.

The excitation functions for the pion-induced reactions $^{27}\mathrm{Al}$(${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$,xN${)}^{18}$F, $^{27}\mathrm{Al}$(${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$,xN${)}^{24}$Na, Si(${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$,xN${)}^{18}$F, and Si(${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$,xN${)}^{24}$Na have been determined for 50- to 390-MeV ${\ensuremath{\pi}}^{+}$ and 50- to 500-MeV ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$. These excitation functions will enable experimenters to monitor high-intensity pion beams by activation of readily available high-purity Al foils or Si disks. The four excitation functions for $^{18}\mathrm{F}$ production and the two for $^{24}\mathrm{Na}$ production by ${\ensuremath{\pi}}^{+}$ show similar (3,3) resonance patterns. However, those for $^{24}\mathrm{Na}$ production by ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ are strikingly different in that the cross sections remain large from the resonance energy on down. This feature is attributed to increasing contributions from ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ absorption and charge exchange with decreasing energy.

Forward-angle differential cross sections at low energies (\ensuremath{\le}80 MeV) are reported for pion single charge exchange to the isobaric analog state for nuclei from $^{7}\mathrm{Li}$ to $^{120}\mathrm{Sn}$. A minimum in the 0\ifmmode^\circ\else\textdegree\fi{} excitation function near 50 MeV persists for all of the measured nuclei and reflects the analogous minimum in the ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}n$ cross section that is caused by a nearly perfect cancellation of the $s$- and $p$-wave $\ensuremath{\pi}$-nucleon amplitudes. The persistence of this feature in these nuclei indicates a strong suppression of the net effect of the medium and constrains the interplay of the medium effects.