The (α,n) production rate of plutonium alpha particles on vermiculite

The (α,n) production rate for plutonium alpha particles on vermiculite relative to that on PuO2 is estimated within the framework of a homogeneous medium model using thick target elemental values evaluated at 5.5 MeV. The composition of the vermiculite is highly variable and the predicted relative (α,n) rate varies over a range of approximately 7–25, but this is in broad agreement with an empirical observation on a particular sample of (13.2 ± 0.7). These results demonstrate that plutonium standards for the calibration of non-destructive assay neutron monitors prepared by the absorption of plutonium nitrate solution onto a vermiculite carrier cannot be considered to be true analogues of plutonium nitrate wastes. Additional information is presented allowing the extension of these results to a variety of other media containing elements of low atomic number with a significant (α,n) production rate.