-----Original Message----- From: Horace Heffner
> Mr. Heffner has kindly done the calculations, and I wouldn't > consider myself qualified to do them right, at least not the first > time! I *never* get anything right the first time. 8^) Whoa. What about elastic collision cross sections? If there is a mistake in your underlying assumptions - then one of them could be this. Al-Najjar et al. (1986) reported that the threshold energy of the neutron required to fission a carbon atom (three alpha) is 9.6 MeV. The authors apparently agree, and cite this reference several times. This is a cutoff, a threshold below which - nada - so if there is an elastic collision of the high energy neutron first, with any hydrogen atom which is half the atoms, then the neutron is lost for further consideration. To do calculation correctly, it would seem that the cross-section for all elastic collisions must be considered first to take this into account. This seems to absent since when you say "Thus 1 in 1/(1.036x10^-3), i.e. 1 in 966 neutrons that is not stopped by O or H is involved in a 12C(n,n')3alpha reaction within 1 mm" but that seems to assume that there is no elastic collision possible with the carbon. Is that true? What am I missing? Jones
