DAMAGE OF POLYVINYLALCOHOL BY 16 MEV ELECTRONS

A stack of seven 15 mu m thick polyvinlyl alcohol (PVA) foils was irra diated with 16 MeV electrons. In order to allow for the electrons' slo wing-down until stopping, six 5 mm thick Al plates had been inserted i n between these PVA foils. The fractional depth distribution of the PV A destruction is derived from the change in the UV-Vis optical spectru m of PVA with depth. The polymer irradiation leads to a shift in the o ptical absorption edges, which indicates a lowering of the energy gap. A convenient explanations of this change is to assume the formation o f carbonaceous clusters. The sizes of these clusters are estimated acc ording to Robertson's theory. Their growth with increasing mean transf erred energy density is compared with the one recorded after ion irrad iation. For the same transferred energy density, energetic electrons a re found to be slightly less efficient in polymer damage than energeti c ions.