Abstract:
Until recently it has been impossibleto conduct experiments in which spectrum-related parameters such as
helium/dpa ratio were varied without also accepting variations in ether important parameters such as
displacement rate and temperature history. A technique currentlv being used, however, allows the study of
the influence of helium alone on density change, microstructuraievolution and mechanical properties. This
technique utilizes isotopic tailoring to vary the helium production rate without introducing changes in
neutron spectrum or displacement rate.1'z By producing alloys whose only difference is the presence or
absence of S_Ni,an isotope that does not occur naturally, and irradiating doped and undoped specimens side
by side in the appropriate reactor spectra, it is possible to generate substantial variations in He/dpa
ratio without varying any other important parameter.
