The chemical consequences of thermal neutron capture in alkali selenates—III

Influence of Cationic Dopants on the Thermal Annealing of Reactor-Irradiated K2SeO4

“…Relation (4) is quite similar to the νπ 1 -e~ki d (1 -R)=Z»° -L·-(5) k t d expression previously proposed for radiation annealing where n° and k i are the relative proportion and rate constant, respectively, for the i th annealing step [16]. However, there is a fundamental difference between the two expressions: whereas the exponential function includes the integral gamma-dose d = φ^ί in expression (5), it is related to a thermal annealing term in equation (4).…”

“…In fact, it would seem that each of these models may account for the experimental results in certain systems and under certain physico-chemical conditions [12], a statement which would apparently hold in the case of K 2 Se0 4 matrices. Reactor-irradiated selenates present some pecu-liarities as compared to the other oxyanions and particularly to K 2 Cr0 4 : 1) they are quite sensitive to ionizing radiation even at liquid nitrogen temperature [15,16]. This observation would indicate that mobile charges which would participate in the annealing process can be created in the solid at low temperature.…”

“…This equation is comparable to that of a series of "/" first order reactions, with rate constants kwhich has been used in some cases for describing the isochronal annealing spectra (v.e.g. [16] for neutron-irradiated K 2 Se0 4 ):…”

“…Gamma-annealing Figure 9a displays a set of calculated R vs. time curves, using differential equations (15)(16)(17) of Appendix 2, for the case of 3 hole-donor species D. with respective k. values of 8X 10" 3 , 2X 10" 4 and 5 X 10" s (arbitrary units), 3 hole-acceptorsplus the acceptor recoil species Ν and impurity M. The formation rate constant of Ν(φ η Κ η ) was taken 10 times smaller than that of the other acceptors (φ Κj) and that of species Μ was proportional to the initial concentration M°. The retention per thermal neutron capture was supposed to be nil.…”

Chemical Effects of the 238U(n,y)239U Reaction and of the 239U→β– 239Np Decay in Solid Uranium Compounds

“…Some solids present a high sensitivity to temperature effects: for example, in the alkali selenates, the charges created by irradiation are mobile and active even at liquid nitrogen temperature [29]. In our case, storing at low temperature (77 K) during ß~ decay, apparently decreases the mobility of charges in some compounds, thus limiting the phenomenon of reduction of 239 Np, while for other compounds this limitation is not effective.…”