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Dispersion curves for phonons propagating in the trigonal direction in bismuth at room temperature and at 7S oK have been obtained in a neutron inelastic scattering experiment. Observed frequencies (units 10 1S rod/sec> at 7S oK are as follows: at the zone center, WTO 1,40 ± 0.02, (tJLO = 1.89 ± 0.02; at the zone boundary in the trigonal direction, WTA 0.73 0.01, Wr,A = 1.12 ± 0.02, WTO = 1.91 ± 0.02, UiLo = 2.03 ± 0.02. At room temperature, the observed frequencies were about 1.5 percent lower. Data were also obtained for longitudinal phonons propagating in the binary direction at 7S oK. It is interesting to note that the splitting between the zone boundary frequencies for the optical and acoustic branches for each polarization is quite large. This splitting is difficult to understand if bismuth is thought of as a slightly distorted simple cubic laltice. The experimental results may be qualitatively understood if bismuth is considered to be made up of a series of double layers normal to the trigonal axis. The atoms in each double layer form a crinkled hexagonal net with strong, probably covalent, bonds between atoms. The forces between atoms on adjacent double layers are relatively weak. This model is consistent with the easy cleavage of bismuth normal to the trigonal axis. Analysis of the trigonal dispersion curves in terms of a linear chain model indicates that there are significant forces connecting a given atom with atoms situated on the four planes on either side of it. 234 ffiM JOURNAL • JULY 1964 235 " -,

Monoergic deuterons from the Minnesota electrostatic generator were used to bombard a thin gaseous target of He 3 . Protons formed in the reaction He 3 (d,p)He i were detected outside the reaction chamber by a Nal scintillation counter. The cross section for the reaction He 3 (d,^)He 4 was measured between the angles of 15° and 130° in the laboratory at deuteron energies of 0.260, 0.455, 0.978, 1.51, 2.01, 2.50, 3.01, and 3.56 Mev. The cross section was measured at a fixed angle of 86° for deuteron energies from 240 kev to 914 kev. A maximum occurred at a deuteron energy of 430±30 kev. The cross section appears to be isotropic in the center-of-mass system in the neighborhood of the maximum. The value of the total cross section at the maximum is 0.90db0.10 barn. Comparison of this value with the upper bound provided by the single level dispersion formula indicates that the spin of the compound state of Li 5 formed in the reaction is f. At 978 kev there is a slight angular dependence of the cross section, which becomes more pronounced at higher energies. At 2.50 Mev the cross section displays a minimum at approximately 113°. At 3.01 Mev the minimum has shifted to 108°, and at 3.56 Mev it appears at 103°. * Supported by the joint program of the U. S. Office of Naval Research and the U. S. Atomic Energy Commission.t.

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