19147

I am concerned about this article. It addresses the mass of fissile materials needed to “make a bomb,” yet it’s clear that the critical masses given–10 kilograms for plutonium-239, 50 kg for uranium-235, and 60 kg for neptunium-237–are for bare spheres with no neutron moderation, reflection, or other factors contributing to going critical. Consider that the International Atomic Energy Agency controls quantities of 8 kg of ²³⁹Pu and 25 kg for ²³⁵U and that these quantities probably relate to masses needed for crude “bombs.” Further, in some processing plants, a mass of about one-half a kilogram is used as a guideline for the minimum quantity of ²³⁹Pu or ²³⁵U, which can, given optimum conditions, go critical. I think the article could mislead people on what quantities need protection.

Robert Marshall
Santa Fe, N.M.