(See the Energy Level Diagram for 5Li)
The excitation curve measured from Ed = 0.2 to 2.85 MeV shows a broad maximum at Ed = 0.45 ± 0.04 MeV (Eγ = 16.6 ± 0.2, σ = 50 ± 10 μb, Γγ = 11 ± 2 eV). Above this maximum, non-resonant capture is indicated by a slow rise of the cross section. The radiation appears to be isotropic to ± 10% at Ed = 0.58 MeV, consistent with s-wave capture (1954BL89). See also (1955KU1B), (1955BA1G; theor.).
Cross sections and angular distributions for reaction (a) from Ed = 35 keV to 10 MeV are given in (1957JA37); see also (1957BO79, 1957FI1A). Below 100 keV the cross section follows the simple Gamow form: σ = (18.2 × 103/E)exp(-91E-1/2) b (E in keV) (1953JA1A, 1954AR02). A pronounced resonance occurs at Ed = 430 keV, of about 450-keV width. The peak cross section is given as 0.695 ± 0.014 b by (1952BO68, 1955KU03) and 0.92 ± 0.07 b by (1953YA02, 1954FR01). The resonance is closely fitted with the one-level dispersion formula, using the parameters listed in Table 5.2 (in PDF or PS) (see 3H(d, n)4He). See also (1955BA1G, 1955HA1B, 1955JO1A, 1956KL1A), (1958PO1A; theor.).
Above Ed = 3.71 MeV, deuteron breakup (reaction (b)) is observed (1955HE90).
Differential cross sections for Ed = 0.4 to 3 MeV are plotted in (1957JA37); see also (1952AL36, 1957BR23, 1957FI1A). In the range Ed = 380 to 570 keV, θc.m. = 65°, the scattering cross section is considerably below Rutherford scattering and is consistent with s-wave formation of a J = 3/2+ state. Above Ed = 2 MeV, the distributions are quite similar to those observed in 3H(d, d)3H (1952AL36, 1954BR05, 1957BR23).
The proton spectrum at E(3He) = 360 keV shows an unresolved ground-state group superposed on a broad continuum. No evidence is found for well-defined proton groups of lower energy than the ground-state group (1954GO18). See also (1953AL1A), (1957BR18) and 6Be.
Differential elastic scattering cross sections have been measured at numerous energies from 0.95 to 95 MeV, as indicated in Table 5.4 (in PDF or PS); curves at several energies are given by (1957JA37) and (1957BR28). Phase shifts derived from the experimental data are listed in the table. At Ep = 40 MeV, the differential cross section shows "diffraction" maxima and minima characteristic of the optical model (1957BR24: see also (1956BU95, 1957GI14, 1957HO1C, 1958GA13)). Recent surveys of the experimental and theoretical situation are reported by (1958GA13, 1958HO1B, 1958MI93).
Even at low energies, the phase shift analysis clearly requires a splitting of P1/2 and P3/2 levels, generally attributed to spin-orbit effect. Either order of the P-doublet can be used to fit the cross section data (1949CR1A, 1952DO30): that the P3/2 state is the lower is established by measurements of the polarization of scattered protons (1952HE15, 1955SC1A, 1956JU10, 1958SC1A). The tabulated phase shifts apply to this case.
The P3/2 phase shift shows a pronounced resonance effect, passing through 90° at Ep = 2.8 MeV (1949CR1A), while the P1/2 changes only slowly over a range of several MeV. Analysis by (1952DO30), based on resonance theory, yields for the P3/2 level (ground state of 5Li) Eλ(c.m.) = -4.1 MeV, γ2λ = 25 × 10-13 MeV-cm and for the P1/2, Eλ(c.m.) = 3.4 MeV, γ2λ = 105 × 10-13 MeV-cm (see also (1952AD09)). (These widths correspond to θ2p = 0.9 and 3.9 times the sum-rule limit, respectively, using R = 2.9 × 10-13 cm.) It thus appears that the P1/2 state, if resonance theory is at all appropriate here, is extremely broad and located 5 - 10 MeV above the ground state. A new analysis of all data < 18 MeV yields Eres(lab) = 2.6 MeV, γ2p = 12 × 10-13 MeV-cm, θ2p = 0.40 for the ground state and Eres(lab) = 10.8 MeV, γ2p = 30 × 10-13 MeV-cm, θ2p = 1.0 for the excited state, using R = 2.6 × 10-13 cm (1958MI93). The s-wave phase shifts are well accounted for by hard-sphere scattering, with R = 2.9 × 10-13 cm (1952AD09, 1952DO30: see, however, (1956VA1C)), R = 2.0 × 10-13 cm (1958MI93). Semi-empirical phase shifts and polarizations for Ep = 10 to 40 MeV are given by (1958GA13).
Proton and neutron scattering in helium are discussed in terms of a central potential with spin-orbit interaction by (1954BR1B, 1954HO1B, 1954JA1A, 1954SA1B, 1955HO1C, 1958GA13). (1955HO1C) obtain a good account of the s- and p-wave interactions with a Gaussian potential and Serber exchange force. The effect of tensor forces is discussed by (1956FE1A). See also (1956AB1A, 1956LE1C, 1958HO1B).
Angular distributions are reported at Ep = 27.9 MeV (1957WI22), 31.6 MeV (1952BE1A) and 95 MeV (1955TE1A) for reaction (a). The cross section at Ep = 40 MeV, θ = 30°, is 10 ± 1 mb/sr (1956EI05). For reaction (b), see (1957WI22) and (1956EI05).
At Ep = 18.6 MeV, the ground-state group appears as a broad, asymmetric peak (Γ = 1.8 MeV) which tails off to a low continuum at lower energies. The angular distribution of the ground-state group has a maximum at 15° (c.m.) and, at small angles, conforms with stripping theory (ln = 1) (1955LI09).
This reaction has been observed at Ep = 17.5 MeV (1957MA04).