Excitation functions for the production of 18F and 24Na from Al and Si with fast pions.

Abstract

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.