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Irradiation strengthening of metals is a result of the barriers to dislocation motion that are produced from precipitation of radiation-induced defects, i.e., vacancies and interstitials. The barriers formed are voids and dislocation loops. In some alloy systems, such as nickel alloys and stainless steels, irradiation-induced precipitation of second phases such as carbides may also contribute to the observed strength increase. While the pinning of dislocations directly contributes to the increase in yield stress, the critical shear stress also increases because it depends on the breakaway of pinned dislocations.