2. Limits to the use of the nuclear microprobe

For the various assay methods used with a nuclear microprobe, the sensitivity and therefore the local detection limit depend on the measurement statistics. Since the number of events detected is proportional to the number of incident ions, a suitable statistic can only be achieved with a microbeam at the cost of increasing the number of charges received per unit area by several orders of magnitude. This can lead to damage that can distort measurement results. A gain in detection efficiency can only push back this limit. The mechanism of particle-matter interactions is beginning to be well understood in the case of electron beams. The same cannot be said for light ion beams with energies of the order of a few mega-electronvolts. Several phenomena can be identified.