Electron collision cross-section measurements and data for gas phase molecules (atoms) of interest to radiotherapy

Detailed analysis and understanding of the early stages of radiation interaction with matter require the knowledge of pertinent electron-molecule collision cross sections. In spite of half a century of activities in this field and a recent increase in demands and efforts to generate cross section data, our knowledge still can be characterized only as fragmentary. In this paper the status of electron-molecule (atom) collision cross section data of interest to radiotherapy is briefly summarized in the low and intermediate-energy regions (about threshold to hundred eV impact energies). The emphasis is on data obtained from measurements carried out under single-collision conditions and associated with elastic scattering, momentum transfer, excitation (rotational, vibrational, electronic), and dissociation into neutral and charged fragments. Differential, integral and total electron collision cross section measurements and theoretical results are discussed and a projection of trends and expectations for the near future is attempted. The recent developments both in experimental and theoretical methods are very encouraging. The optimum approach to the generation of the very large body of data required is a joint experimental-theoretical effort. (Theoretical methods are not yet completely reliable and need experimental verifications. On the other hand, experimental determination of a detailed and complete set of cross sections is a difficult and tedious job; it is overwhelming in general and practically impossible in some cases.) (author). 63 refs, 5 figs, 1 tab