[en] Inner surfaces of a Pt-10% Rh capsule exposed at room temperature to alpha particles and fission fragments in a large ²⁵²Cf source showed many small blisters, with elongated configurations in some areas. Formation of the blisters was attributed to the fission-fragment-induced agglomeration of helium implanted by the alpha particles, coupled with a stress relieving transport of lattice atoms displaced by the fission fragments into the blister walls. Lateral and vertical elongation of the blisters resulted from concentration gradients of implanted helium and displaced atoms along the capsule wall. Although no significant deterioration of the ²⁵²Cf capsule resulted, the observed blistering could have important consequences for materials applications in other complex radiation environments