A reactor is fueled with natural uranium and moderated with Teflon (CF₄), having NM/NF = 700 ratio of moderator molecules to fuel molecules. Use data in Table 10.3 of the textbook ('Graphite' is Carbon), plus
Element σₛ σₐ
¹⁹F 3.74 b 9.6 mb
(the cross-sections are given for thermal neutrons; the only stable isotope of Fluo- rine is ¹⁹F and assume that all of the Carbon is the same as 'graphite' in nuclear properties)
Calculate the average log-decrement (ξ) of the moderator