Study of the Neutron ReactionsLi6(n, α)H3,F19(n, γ)F20, andI127(n, γ)I128

Abstract

The reactions ${\mathrm{Li}}^{6}(n, \ensuremath{\alpha}){\mathrm{H}}^{3}$, ${\mathrm{F}}^{19}(n, \ensuremath{\gamma}){\mathrm{F}}^{20}$, and ${\mathrm{I}}^{127}(n, \ensuremath{\gamma}){\mathrm{I}}^{128}$ were studied using scintillating crystals both as targets and as detectors. The neutrons were produced by the ${\mathrm{Li}}^{7}(p, n){\mathrm{Be}}^{7}$ and ${\mathrm{T}}^{3}(p, n){\mathrm{He}}^{3}$ reactions. A redetermination of the ${\mathrm{Li}}^{7}(p, n){\mathrm{Be}}^{7}$ differential cross section was made in the proton energy range 1.9 to 3.0 Mev at 0\ifmmode^\circ\else\textdegree\fi{} and the cross section observed at 2.27 Mev was 154 mb. Cross sections for this reaction were determined at 120\ifmmode^\circ\else\textdegree\fi{} for proton energies below 2.4 Mev and at 60\ifmmode^\circ\else\textdegree\fi{} for energies below 2.1 Mev. The ${\mathrm{Li}}^{6}(n, \ensuremath{\alpha}){\mathrm{H}}^{3}$ reaction cross section was studied for neutron energies between 0.025 and 4 Mev. The resonance at 0.255 Mev was observed to have a width (lab) of 0.125 Mev and a maximum cross section of 2.80 barns. A fit of the dispersion theory to this resonance yielded the following parameters in the center-of-mass coordinates: ${{\ensuremath{\gamma}}_{n}}^{2}=0.41$ Mev-cm, ${{\ensuremath{\gamma}}_{\ensuremath{\alpha}}}^{2}=0.015$ Mev-cm, ${\ensuremath{\Delta}}_{\ensuremath{\lambda}}=0.17$ Mev, ${E}_{\ensuremath{\lambda}}=0.039$ Mev, and $\ensuremath{\Gamma}=0.188$ Mev at the resonant energy. Sixteen resonances were observed in the ${\mathrm{F}}^{19}(n, \ensuremath{\gamma}){\mathrm{F}}^{20}$ reaction at neutron energies of 0.027, 0.048, 0.100, 0.177, 0.270, 0.308, 0.388, 0.425, 0.500, 0.600, 0.760, 0.865, 0.950, 1.125, 1.290, and 1.635 Mev. The radiative widths ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ of twelve of these resonances vary between 1.1 and 8.6 ev. A monotonically decreasing cross section was observed for the ${\mathrm{I}}^{127}(n, \ensuremath{\gamma}){\mathrm{I}}^{128}$ reaction between 0.025 and 0.500 Mev.