The reactions ${\mathrm{Li}}^6(n, \alpha ){\mathrm{H}}^3$, ${\mathrm{F}}^{19}(n, \gamma ){\mathrm{F}}^{20}$, and ${\mathrm{I}}^{127}(n, \gamma ){\mathrm{I}}^{128}$ 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° and the cross section observed at 2.27 Mev was 154 mb. Cross sections for this reaction were determined at 120° for proton energies below 2.4 Mev and at 60° for energies below 2.1 Mev. The ${\mathrm{Li}}^6(n, \alpha ){\mathrm{H}}^3$ 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: ${{\gamma }_n}^2=0.41\mathrm{}$ Mev-cm, ${{\gamma }_{\alpha }}^2=0.015\mathrm{}$ Mev-cm, ${\Delta }_{\lambda }=0.17\mathrm{}$ Mev, $E_{\lambda }=0.039\mathrm{}$ Mev, and $\Gamma =0.188\mathrm{}$ Mev at the resonant energy. Sixteen resonances were observed in the ${\mathrm{F}}^{19}(n, \gamma ){\mathrm{F}}^{20}$ 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 ${\Gamma }_{\gamma }$ of twelve of these resonances vary between 1.1 and 8.6 ev. A monotonically decreasing cross section was observed for the ${\mathrm{I}}^{127}(n, \gamma ){\mathrm{I}}^{128}$ reaction between 0.025 and 0.500 Mev.

• Received 3 November 1958

DOI:https://doi.org/10.1103/PhysRev.114.201