Does anybody know about a web site where neutron cross sections for various
isotopes (thermal energies and above, up to 1 MeV or so) can be found?
Do we have a good explanation of tremendous differences in cross secions
(at thermal and above thermal energies) for nearly identical nuclei? Looking
at the old Evans textbook, "The Atomic Nucleus" (page 443) I see the first
resonance in Cd (Z=48) at 0.18 eV while in Ag (Z=47) the first resonance is
at 4.9 eV. Why is it so?
Or why is the thermal cross section for B ten times larger than for Ag (500
versus 50 barns)? B has no nearby resonances but its total cross section is
much larger than that of Ag. The nearby resonance in Ag should enhance the
capture probability but just the opposite is observed. [The PI*lambda^2 are
identical in both cases and each nucleus is much smaller than lambda.]
Am I missing something important in trying to rationalize this empirical
information?
Ludwik Kowalski