Imaging of multi-ionization spurs from low LET radiations absorbed by polymers

Complete text of publication follows. Distribution and kind of spurs resulting from absorption of low LET radiation was discussed practically only for the case of water. The early developments have clearly distinguished the presence of single ionization spurs, as the origin of radical products of water radiolysis and multi-ionization spurs yielding molecular products, i.e. H2 and H2O2. Mechanism of spurs formation was shown by Henglein in his 'Strahlenchemie' monograph. Limitation of that picture to aqueous systems is not justified, because it is valid for any low Z medium and we expect the same phenomena in polymers as well. 80% of deposited energy is distributed in single spurs and the rest in multiionization spurs, formed as congestion of several ionizations very close to one another. Almost reversed situation is in the case of high LET radiations, where the most of energy is forming multi-ionization spurs, as in the case of alpha radiation. The latter produces in water mainly H2 and H2O, due to the domination of overlapping of ionization spurs and low yield of radical products. The same phenomenon of concentrated deposition of energy in the zone of multi-ionizations must occur in any condensed phase. Indeed, polycarbonates are applied to the determination of radon. Alpha particle absorbed on the surface of polycarbonate film causes local damage prone to etching by NaOH solution. Resulting micro-holes are easily counted. Single ionization spurs are not affected by etching. In our case of low LET, the participation of multi-ionization spurs is lower, but they are present and we have applied the similar technique, taking into account the facts of smaller size of multi-ionization spheres and the fact of reaching the etching solution only to spurs present at the surface of the film. Pictures in the text of the presentation show the effects of experiments. Semiquantitative estimate of yields confirms the expected, ∼20% yield of multi-ionization spurs. The dominating effects by low LET radiations (EB and γ) consists in chemical effects starting in single ionization spurs (crosslinking and degradation), present results show, it is worthwhile to look into effects caused by multi-ionization spurs, e.g. sites of higher degradation, of specific products formation, and/or formation of gases.