Chemical states and thermal annealing of the 131I, 133I and 135I formed by 235U fission produced by thermal neutron irradiation of uranyl chloride at room and liquid nitrogen temperatures

In uranyl chloride irradiated by thermal neutrons the initial values of the percentages of reduced iodine forms are: 68.2% for 131I, 67.7% for 133I and 76.4% for 135I, at the channel temperature and 73.3, 69.9 and 77.4% respectively in liquid nitrogen. By thermal annealing of the neutron irradiated samples the percent of the reduced forms increases for all three isotopes during the first 2 to 4 hr. At longer annealing time an oxidation process occurs progressively at 1000C and a pseudo-plateau is noticed at 130 to 1500C for 131I and 133I isotopes. In the case of 135I the pseudo-plateaux were obtained after a visible decrease of the reduced form. For the interpretation of the experimental results in the thermal annealing process of the reducing action of the deformed fission matrix and the oxidising action of the species diffusing from the track of the fission fragments have been considered. (author)