ENERGY DEPOSITION AND FRAGMENTS PRODUCTION RESULTING FROM GAMMA-RAY OR ION-BEAM IRRADIATION OF AN ION-EXCHANGE RESIN

The extraction efficiency of ion exchange resins aimed at the reproces sing of nuclear effluents is strongly dependent on gamma-ray induced m odifications of their chemical structure. A poly(4-vinylpyridine) resi n, or P4VP, has been subjected to gamma irradiation using a Cs-137 sou rce (E(gamma) = 662 keV) and we have attempted to characterize its str uctural modifications using TOF-SIMS techniques based on low (keV) and high (MeV) primary ion beam energies. These analytical techniques are based on the formation of fragments resulting respectively from atomi c and electronic collisions of heavy ions. As a result, the difference s in nature and relative intensity of the emitted secondary ions, as w ell as the variation of their intensity as a function of the absorbed dose of gamma rays (up to 14 400 kGy), can be interpreted from differe nt types of bond breaking. While gamma-ray absorption results in benzy lic or pyridinic scissions, MeV ion bombardment may induce simultaneou s (and close) pyridinic-pyridinic or pyridinic-benzylic scissions, or both. Accordingly, the technique is very sensitive to the presence of fragments preformed under gamma irradiation. This is not observed with keV bombardment which may destroy the pyridine nucleus. The SIMS anal ysis of the soluble fraction of the irradiated material (free radicals and fragments) and of the remaining material confirms the proposed fr agmentation paths leading to positive and negative ion emission. Such results fully support the important finding that these gamma-ray induc ed modifications are only observed from negative emission under MeV io n bombardment.