Unpaired electron statistics in irradiated LiF

On the basis of a simplified model, average concentrations of unpaired electrons in neutron irradiated single crystals of lithium fluoride were calculated by the Monte-Carlo method. A preliminary study is made of a one-dimensional model, in which case the Monte-Carlo calculations are checked by solving the corresponding differential equations. The final three-dimensional version results in a curve, representing the calculated concentration of unpaired electrons versus the defect concentration. The curve is similar in shape to the one obtained from magnetic susceptibility data versus neutron dose. The absolute value of the maximum concentration is about the same for both curves. Two assumptions in particular lead to this result: 1. (1) The electrons of adjacent defects are thought to form 'non inert' pairs, and 2. (2) The newly formed defects are allowed to migrate over a few lattice distances toward existing centres.