Defect production in purified and nitrogen doped niobium during low temperature neutron irradiation

Abstract

During low temperature reactor irradiation up to a neutron dose of 2.7 : times; 10¹⁸ cm⁻² the electrical resistivity increase was measured at 19 K on purified niobium and niobium doped with nitrogen up to 850 at. ppm. From the equality of the extrapolated saturation value of the resistivity with that after electron irradiation it is concluded that the defect cascades are loosely packed. A strong initial decrease of the damage rate of the purified Nb can be quantitatively accounted for by assuming that a relatively large fraction of the self-interstitials is produced by means of long range focusing collision sequences. A pronounced increase of the damage rate with nitrogen content is discussed in terms of capturing of focusing collision sequences at interstitial impurities and of a reduction of the fraction of self-interstitials produced by such collision sequences.