Tests of tissue-equivalence for negative pions

The results presented in brief tabular form, support the authors' earlier conclusions on the extent to which materials that are tissue-equivalent for x-rays and electrons are also tissue-equivalent for pions. In particular, the following points are noted: (i) TE plastic gives very poor results, (ii) glucose is not really satisfactory and none of the other saccharides studied give better results, (iii) pure water does not reproduce the intensity pattern for oxygen in tissues nearly as well as might be expected, (iv) the best results are for TE liquid and the amino acids, all of which contain nitrogen, as well as carbon, oxygen and hydrogen, and for Perspex. The interpretation of the pionic x-ray data involves the assumption that the pion can go into a molecular orbit before transferring to a particular atom, implying that successful definition of tissue-equivalence for pions requires consideration of molecular structure. (author)