On Sat, Mar 23, 2013 at 5:11 PM, <[email protected]> wrote: Then you should be able to follow the same procedure, but include all the > natural isotopes, no? >
I've gone back and corrected the calculation to take into account the missing isotopes. This time I obtained upper and lower bounds for the total cross section, from both Robin's Web site [1] and Lou's site [2], and I did the calculation using Robin's method along with a modified version of that method. Here are the estimated upper and lower bounds for the total neutron cross sections for nickel as it is found in its natural isotopic abundances. The combined cross sections are the weighted values of the cross sections for individual isotopes of nickel. UB Kaeri: 206 barns LB Kaeri: 45 barns UB NDS: 94 barns LB NDS: 29 barns On the basis of these cross sections, I calculated the upper and lower bounds for the transmitted fraction of an incident beam of neutrons at 1mm and 10mm, using Robin's approach as well as a modified version of Robin's approach relying upon the mean free path described in Wikipedia's article on the neutron capture cross section [3]. The two sets of calculations agreed to within two degrees of precision, which was nice to see. Since they agreed, I'll just give the transmitted percentages using Robin's approach: UB, 1mm: 76.6 percent LB, 1mm: 15.2 percent UB, 10mm: 7 percent LB, 10mm: small For 1W of power being generated by way of neutron capture, assuming around 10 MeV per capture, there would be about 624 billion neutrons generated per second. The number of neutrons per second that would be transmitted through 1mm and 10mm of inactive nickel shielding would be: UB, 1mm: 478 billion LB, 1mm: 94 billion UB, 10mm: 43 billion LB, 10mm: 4000 This assumes that there are no neutrons being generated in the nickel shielding surrounding the active core, an assumption that runs counter to conjecture that LENR (in Pd/D) is a surface effect. An interesting thing that I discovered as I was looking into this was that Robin's Web site and Lou's Web site disagree significantly on what happens to the total cross sections when the energies are small. In general, Robin's Web site gave values that were well below the maximums, at around 10E-4 MeV, while Lou's site gave values that were highest at the very lowest energies, around 10E-10 MeV. I'm not sure what was going on there. Just to be safe, the above calculations make use of both the cross sections at the lowest energies as well as the maximum values for the cross sections. It interesting to note that the combined cross section can be expected to go way up as 58Ni transmutes to 59Ni, which normally exists in trace amounts but would build up over time, as 59Ni has an extremely large neutron capture cross section. Note that nickel would become dangerously radioactive over time as it was activated under this kind of neutron flux. Eric [1] http://atom.kaeri.re.kr/ [2] http://www-nds.iaea.org/ngatlas2/ [3] http://en.wikipedia.org/wiki/Neutron_cross_section
