Corrections to measurements of pion capture ratios

Abstract

The authors have recently reported measurements of pionic X-rays from some organic molecules (Jackson et al., Phys. Rev. A, vol.25, p.326, 1982), tissues and tissue-equivalent materials (Lewis et al., ibid., vol.27, p.683, 1982). The intensities of the X-ray lines in the Balmer series in carbon and in oxygen were summed to give the C/O pion capture ratios, which showed marked departures from the Fermi-Teller Z-law. The dependence of the capture ratios on molecular structure has raised serious questions about the effect on dose calculations for pion radiotherapy (Lewis et al., 1982, G. Buche private communication) and on the definition of tissue equivalence for pions (Jackson, 1982). It is concluded that the electromagnetic corrections to the C/O pion capture ratios deduced from the summed intensities of pionic Balmer series are small, and much less than the authors experimental errors. The magnitude of the correction due to nuclear absorption depends on the initial angular momentum distribution which in turn depends on molecular structure.