Atomic data required for the calculation of local energy deposition near isotopes decaying by electron capture or internal conversion

There is a group of isotopes widely used both medically and as tools in radiobiological research which decay by electron capture and/or internal conversion. These isotopes have the general characteristic of a very high energy deposition localized within a few nanometres of the decay, in addition to the energy that is delivered by gamma rays and long range electrons. Such very local energy deposition will produce high LET-like effects if the decay is located in or very near a sensitive site, or low LET-like effects if removed from sensitive sites. Two mechanisms are responsible for the short ranged radiation effects: (a) the emission of very low energy electrons produced by transitions between higher orbitals; these occur when the atom is already multiply ionized and their energies and transition rates are difficult to estimate, and (b) the emission of many electrons produces a charging and subsequent neutralization of the daughter atom. The charging produces considerable potential energy which is released by the neutralization. The neutralization is a complex process and the collection of charge from neighbouring atoms will produce a cluster of ions around the daughter atom. There is also evidence that some of the electrons collected are re-emitted. Techniques for the evaluation of the local energy deposition will be described and the relative importance of the two short range components of the dose will be presented. (author). 28 refs, 1 fig., 1 tab