Exposure rate constants for filtered 192 Ir sources

The exposure rate constant, Γ δ was recently calculated to be 4.69±0.05 R cm 2 h −1 mCi −1 (9.09×10 −19  C kg −1 m 2 s −1  Bq −1 ) for an unfiltered point source of 192 Ir. Using that same nuclear spectroscopy data filtered exposure rates constants have been calculated for encapsulated sources produced by two commercial manufacturers. For a 0.3 mm diam. spherical source with a 0.1 mm core of 25% Ir and 75% Pt encased in a sheath of 0.1mm 100% Pt, the calculated filtered exposure rate constant is 4.30±0.10 R cm 2 h −1 mCi −1 (8.33×10 −19  C kg −1 m 2 s −1  Bq −1 ). For a 0.5 mm diam. spherical source with 0.1 mm diam. core of 25% Ir and 75% Pt encapsulated in 0.2 mm stainless steel, the calculated filtered exposure rate constant is 4.45±0.10 R cm 2 h −1 mCi −1 (8.62×10 −19  C kg −1 m 2 s −1  Bq −1 ). Calculational details are presented.