The disintegration of B10 and F19 by fast neutrons

The disintegration of B10 and F19 by fast neutrons has been studied using a grid-type ionization chamber filled with argon and boron trifluoride enriched in B10. Monoenergetic neutrons for studying the reactions from 0.2 to 8.2 MeV were produced with the Li7 (p, n)Be7, T(p, n)He3 and D(d, n)He3 reactions. Alpha groups from the B10((n, α)Li7 reaction leaving Li7 in its ground and first excited state at 478 keV were studied over the entire energy range. The cross section for the (n, α) reaction decreased rapidly from 1048 mb at 0.2 MeV to 180 mb at 1.2 MeV and then increased to 451±60 mb at the 1,84 MeV resonance. For higher energies broad resonance structure was observed with the cross section generally decreasing and reaching a value of 31 mb at 8.2 MeV. The B10(n, t2α) reaction was observed for neutron energies above 1.3 MeV. The cross section for this reaction increased to 80 mb at 4.5 MeV and was comparable to that for the B10(n, α)Li7 reaction above 5 MeV. The B10 (n, t2α) reaction was found to proceed mainly by three-body breakup or through the 4.63 MeV excited state of Li7. Some reactions may have proceeded through the 2.9 MeV level of Be8 but few, if any, proceeded through the ground state of Be8. The total excitation function for the F19(n, α)N16 reaction leaving N16 in the ground and first three excited states was studied for neutron energies above 2.9 MeV. Ten resonances were observed. The cross section increases to 135±50 mb at 5.80 MeV and then decreases at higher energies.

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