Whisker growth - a new mechanism for helium blistering of surfaces in complex radiation environments

Implantation of helium concurrent with the generation of displaced atoms in surface layers of materials exposed to 252Cf α-particles and fission fragments produces a unique form of low temperature surface blistering. Observations of vertically elongated blisters, among other configurations, formed under such conditions suggest that the blisters result from a whisker-growth mechanism. In this mechanism the blisters, like filamentary whiskers on certain electroplated metals represent a surface deformation that relieves the lateral compressive stresses developed in the material during helium implantation. The implanted helium combines with vacancies resulting from atom displacements by the fission fragments to produce gas bubbles, leaving residual interstitial atoms around the bubbles to form whisker-like walls. Such a mechanism may under some conditions contribute to surface blistering in other complex radiation environments, such as the thermonuclear reactor. The purpose of this paper is to formulate a basis for the whisker-growth mechanism for helium blistering as an aid to the specification of conditions under which the mechanism might apply. (Auth.)