Neutron irradiations of silicon studied by Fe-57 Mössbauer effect

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Abstract
Fast neutron irradiations of silicon are studied through the cobalt-57 probe incorporated into the lattice. The cobalt substitutional atoms introduced by fast quenching from around 1100°C are found to be converted to interstitials by reactor irradiations at 80°C. The reverse effect in which the irradiations enhance the substitutional atoms also takes place. These conversion effects are accompanied by a marked dependence upon initial Fermi levels. Their efficiencies seem to be proportional to integrated neutron flux. A strong unstable spectrum best represented by 4 quadrupolar doublets arises before the interstitial-type conversion is observed. These doublets are tentatively assigned to the cobalt interstitials trapped by charged centers. The spectrum dies out with the decay of the induced radiation, suggesting that the pairs become unstable at thermal equilibrium at room temperatures.