The effect of helium on cavity swelling in dual-ion irradiated Fe and Fe-10Cr ferritic alloys

•Cavity swelling peaked at an intermediate He implantation rate ∼10 appm He/dpa for ion irradiated Fe and fe-10cr alloys.•A bimodal cavity size distribution was observed in the 10 and 50 appm He/dpa samples but not for 0.1 appm He/dpa.•Treating small bubbles as bias sinks can significantly change the biased to unbiased sink strengths ratio (Q) and the capture efficiency ratio (Z).•Assuming the same z ratio for all He/dpa ratios may be physically incorrect.