Preparation and characterisation of 239Pu and 240Pu thin films as sources for 235mU and 236U recoil ions
摘要
Recoil-ion sources of 239Pu and 240Pu, providing recoiling alpha-decay daughters 235 mU and 236U, were prepared by molecular plating. Comprehensive radiographic, microscopic and spectroscopic characterisation revealed thickness-dependent morphology, homogeneity, and activity distributions. Since neither recoil ion can be readily detected, 239Pu sources spiked with 228Th were also prepared to provide readily detectable 224Ra daughter ions. Geant4 simulations, validated against 224Ra surrogate measurements, reproduce recoil escape efficiencies within ~ 3%. 239Pu and 240Pu recoil-ion sources with thicknesses of ~ 40–55 nm produce the highest recoil rate per unit area and highest layer quality across the 24–108 nm thickness range.