Norway and Sweden to Cooperate on Development of Lead Cooled Small Nuclear Reactors.

[NNadir]

4. I'm not sure whence that 5333 barn figure comes. The ENDF 7.1 scattering plot for 3He suggests a lower figure.

I'm curious. Perhaps you can share the reference. You've raised my curiosity.

Here's the plot for ³He:



Here's the plot for ⁴He:



Evaluated Nuclear Data File (ENDF) Retrieval & Plotting

It is important to note that even at a low scattering cross section, the average energy loss from elastic scattering is highest for light nuclei.

Without going too much into the mathematics of elastic scattering of neutrons, and energy loss, the number of collisions to thermalize a neutron from 2 MeV to 1 ev is reportedly 14 for H, 20 for ²H and 43 for ⁴He.

cf: Stacy, Nuclear Reactor Physics, 1st edition, 2001, Wiley, page 31. (I haven't opened that book for a long time.)

By the way I was wrong about the nonexistence of ⁵He and ⁸Be. It would appear that the sensitivity at which time intervals can be measured is now so great, that they can be transiently detected with extremely short half-lives, on the order of 10^-22 seconds for ⁵He and 10^-18 seconds for ⁸Be . I can't imagine that there would be any way to measure the capture cross section for such a short lived nuclei. ⁵He decays, of course, by neutron emission, but this would suggest that even in such a short existence period, that this would have the effect of slowing neutrons, since gamma emission would be involved. ⁸Be decays by symmetric double alpha, call it fission or whatever.

Your comments caused me to look deeper into the matter for which I thank you.