Energy deposition and fragments production resulting from gamma-ray or ion beam irradiation of an ion exchange resin

Abstract

The extraction efficiency of ion exchange resins aimed at the reprocessing of nuclear effluents is strongly dependent on gamma-ray induced modifications of their chemical structure. A poly(4-vinylpyridine) resin, or P4VP, has been subjected to gamma irradiation using a 137Cs source ( E γ = 662 keV) and we have attempted to characterize its structural 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 atomic and electronic collisions of heavy ions. As a result, the differences in nature and relative intensity of the emitted secondary ions, as well 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 different types of bond breaking. While gamma-ray absorption results in benzylic or pyridinic scissions, MeV ion bombardment may induce simultaneous (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 analysis of the soluble fraction of the irradiated material (free radicals and fragments) and of the remaining material confirms the proposed fragmentation paths leading to positive and negative ion emission. Such results fully support the important finding that these gamma-ray induced modifications are only observed from negative emission under MeV ion bombardment.