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5He (1984AJ01)

(See Energy Level Diagrams for 5He)

GENERAL: See also (1979AJ01) and Table 5.1 [Table of Energy Levels] (in PDF or PS) here.

Model calculations:(1978RE1A, 1979JA31, 1979KA06, 1979LU1A, 1979MA1J, 1980HA1M, 1981BE10, 1981KR1J, 1982FI13).

Special states (The first T = 5/2 state of 5He is predicted to lie at Ex ≈ 40 MeV (1981BE25; theor.).): (1979JA31, 1981BE10, 1981KU1H, 1982EM1A, 1982FI13, 1982FR1D).

Complex reactions involving 5He:(1979BR02, 1979RU1B).

Reactions involving pions:(1978FI1D, 1979BA16, 1981WH1D, 1982WH1A, 1983HUZZ).

Reactions involving antiprotons:(1981YA1B, 1981YA1C).

Hypernuclei:(1978PO1A, 1978SO1A, 1979BU1C, 1979ZO1A, 1980BA1X, 1980IW1A, 1980SC1H, 1981BA2N, 1981BA2Q, 1981KU1H, 1981LY1B, 1981RA18, 1981RE1B, 1981WA1J, 1982BA1P, 1982DA1H, 1982FI1K, 1982JO1C, 1983GI1C, 1983JO1E).

Applied topics:(1982GO1R).

Other topics:(1978BE48, 1978RO17, 1979KA06, 1980AM1B, 1982BA1P, 1982LA11, 1982NG01).

Ground state of 5He:(1979BR02, 1981AV02, 1981BE10, 1982EM1A, 1982FI13, 1982KU1C, 1982NG01).

1. 3H(d, γ)5He Qm = 16.70

At low energies the reaction is dominated by a resonance at Ed = 107 keV; the mirror reaction shows resonance at Ed = 430 keV. The cross section for emission of 16.7 MeV γ-rays for Ed = 25 to 100 keV has been measured: the ratio σ(d, γ)/σ(d, n) is approximately constant at (2.1 ± 0.6) × 10-4, leading to Γγ = 14 ± 4 eV, where Γn is taken as 66 keV. The cross sections derived from thick target yields from Ed = 150 to 1300 keV are analyzed into resonant and direct-capture contributions: there is disagreement about the cross section at resonance: see (1979AJ01). At Ed = 1.03 ± 0.05 MeV, the differential cross section is 0.44 ± 0.12 μb/sr (90°) and the γ to n branching ratio is an order of magnitude smaller: 2.3 × 10-5. The angular distribution of the γ-rays is forward peaked and the total cross section is estimated to be 4.8 μb: see (1979AJ01).

2. (a) 3H(d, n)4He Qm = 17.5894 Eb = 16.70
(b) 3H(d, 2n)3He Qm = -2.9883
(c) 3H(d, pn)3H Qm = -2.2246

Below Ed = 100 keV, the cross section for reaction (a) follows the Gamow function, σ = (A/E) exp (-44.40E-1/2). A strong resonance, σ(peak) = 5.0 b, appears at Ed = 107 keV: see Table 5.2 (in PDF or PS). From Ed = 10 to 500 keV, the cross section is well fitted with the assumption of s-wave formation of a Jπ = 3/2+ state. Excitation curves and angular distributions for reaction (a) have been measured from Ed = 8 keV to 21 MeV and at Et = 20.00 MeV [see (1974AJ01, 1979AJ01) for the earlier references] and at Et = 12.5 to 117 keV (1983BR1G; σt), 7.49 to 16.65 MeV (0° excitation function; ± 1.0 → 4.4%) and Ed = 7, 10, 13.36 and 16.5 MeV (angular distributions) (1978DR08) [see also for a review of other work on this reaction].

A study of reaction (a) with polarized deuterons at Ed = 0.2 to 1.0 MeV indicates intervention of the s-wave, Jπ = 1/2+ channel, as well as possible p-waves above Ed = 0.3 MeV. At higher energies, the neutron polarization P11) shows an angular distribution that peaks typically at θ1 = 30° lab, then goes negative with increasing angle and has a minimum between 90° and 130°, depending upon energy. (1971MU04) have made an extensive study of P1(30°) for Ed = 5 to 15 MeV and, with deuterium as target, for Et = 4.5 to 19.5 MeV (neutrons near 135° lab). The polarization increases monotonically from 0.03 at Ed = 3 MeV to ≈ 0.5 at Ed = 6.5 MeV and then with a lower slope to 0.69 at Ed = 13 MeV. The change in the slope may be caused by excited states of 5He near 20 MeV. Comparison with the 3He(d, p)4He mirror reaction at corresponding c.m. energies shows excellent agreement between the polarization values in the two reactions up to Ed = 6 MeV, but then the proton polarization becomes ≈ 15% higher, converging back to the neutron values at Ed ≈ 12 - 13 MeV. This may be due to experimental factors (1971MU04). The tensor analyzing power of Azz(0°) has been measured for Epol. d = 0.24 to 6.75 MeV: large differences in Azz(0°) for this reaction and for 3He(d, p) are reported for Epol. d < 1.65 and > 4 MeV (1980DR01). See however (1980GR14). See also (1981CL1B, 1981DE2E; prelim.). For other polarization studies see (1974AJ01, 1979AJ01) and (1982SA05: Ed = 37.1 MeV).

(1981JA1F) suggests that errors of as much as 50% are possible in the reactivity values for Ed = 10 to 100 keV, probably because of energy-scale errors: this will affect the fusion probability errors in reactor calculations. The astrophysical S function has been obtained by (1983BR1G) for the equivalent Ed = 8.3 to 78.1 keV.

Reaction (b) has been studied for Ed = 10.9 to 83 MeV: see (1974AJ01, 1979AJ01). A reanalysis of the work of (1963PO02) on reaction (c) by (1974SC04) leads to the suggestion of a resonance at Ec.m. = 2.9 ± 0.3 MeV [Ex = 19.6 MeV], Γc.m. = 1.9 ± 0.2 MeV, consistent with Jπ = 3/2- [see, however, Table 5.1 (in PDF or PS)]. For muon catalysis see (1981BY1E, 1982BE1P, 1982BR1R, 1983JO1F).

See also (1979BA2X, 1979OH1B, 1981HA1P), (1980DR1C, 1981DR05, 1982RA1A), (1978BA1F, 1979FO1R, 1979GR1P, 1979GR2D, 1979HA2C, 1980BR1D, 1980PE1J, 1981HA1N, 1982HE1F, 1982MI1E, 1982RA1F; applications) and (1978FI1D, 1981BE1P, 1981BO2C, 1981BR1G, 1981GE1C; theor.).

3. 3H(d, d)3H Eb = 16.70

The elastic scattering has been studied for Ed = 2.6 to 11.0 MeV [see (1979AJ01)] and at Et = 0.6 to 3.4 MeV (1979KA33). The excitation curves show an interference at Ex ≈ 19 MeV and a broad (Γ > 1 MeV) resonance corresponding to Ex = 20.0 ± 0.5 MeV, similar to that seen in 3He(d, d) [see 5Li]. Together with data from 3H(d, n)4He, this work favors an assignment D3/2 or D5/2 with a mixture of doublet and quartet components (channel spin 1/2 and 3/2) if only one state is involved [any appreciable doublet component would, however, be in conflict with results from 7Li(p, 3He)5He]. Measurements of differential cross section and analyzing power using polarized deuterons with Ed = 3.2 to 12.3 MeV show resonance-like behavior in the vector analyzing power near Ed = 5 MeV. The anomaly appears in the odd Legendre coefficients and is interpreted in terms of a (1/2, 3/2)- excited state of 5He with Ex ≈ 19.6 MeV. Broad structure in the differential cross section near 6 MeV, principally in the even Legendre coefficients, corresponds to an even-parity state 5He*(20.0). For other polarization measurements (and for references) see (1979AJ01). See also (1978TA1A, 1981BO2C; theor.).

4. (a) 3H(t, n)5He Qm = 10.44
(b) 3H(t, 2n)4He Qm = 11.3322

At Et = 0.5 MeV, the reaction appears to proceed via three channels: (i) direct breakup into 4He + 2n, the three-body breakup shape being modified by the n-n interaction; (ii) sequential decay via 5He(0); (iii) sequential decay via a broad excited state of 5He. The width of 5He(0) is estimated to be 0.74 ± 0.18 MeV. Some evidence is also shown for 5He* at Ex ≈ 2 MeV, Γ ≈ 2.4 MeV: see (1979AJ01). For reaction (b), see 6He.

5. (a) 3He(t, p)5He Qm = 11.21
(b) 3He(t, pn)4He Qm = 12.0959

Some evidence is reported at Et = 22.25 MeV in reaction (a) for a broad state of 5He at Ex ≈ 20 MeV, in addition to a sharp peak corresponding to 5He*(16.7): see (1979AJ01). For reaction (b) see 6Li.

6. 4He(n, n)4He Eb = -0.89

The coherent scattering length (thermal, bound) is 3.07 ± 0.02 fm, pol. σs = 0.76 ± 0.01 b (1981MUZQ). Total cross sections for En = 4 × 10-4 eV to 150.9 MeV and at 10 GeV/c are summarized in (1974AJ01, 1976GAYV). For polarization measurements see (1974AJ01, 1979AJ01) and (1983YO01; En = 50.4 MeV).

The total cross section has a peak of 7.6 b at En = 1.15 ± 0.05 MeV, Ec.m. = 0.92 ± 0.04 MeV, with a width of about 1.2 MeV. A second resonance is observed at En = 22.15 ± 0.12 MeV, corresponding to the 16.7 MeV Jπ = 3/2+ state: Γc.m. = 100 ± 50 keV [see (1979AJ01) for references]. Γn = Γd = 45 ± 10 keV (1981MUZQ). [(1966HO07) find that the data are fitted best by Γn < Γd although Γn > Γd is not excluded]. Attempts to detetct additional resonances in the total cross section have been unsuccessful: see (1966LA04).

The P3/2 phase shift shows strong resonance behavior near 1 MeV, while the P1/2 shift changes more slowly, indicating a broad P1/2 level at several MeV excitation. (1966HO07) have constructed a set of phase shifts for En = 0 to 31 MeV, l = 0, 1, 2, 3 using largely p-α phase shifts. At the 3/2+ state the best fit to all data is given by Eres = 17.669 MeV ± 10 keV, γ2d = 2.0 MeV ± 25%, γ2n = 50 keV ± 25% (see Table 5.2 (in PDF or PS)). The work of (1976LI15) indicates some discepancies with the results of (1966HO07) [below En = 22 MeV].

An R-function analysis of the 4He + n data below 21 MeV (including the absolute neutron analyzing power measurement of (1976BO05) and the accurate cross-section measurements of (1973GO38) has led to a set of phase shifts and analyzing powers which are based on the 4He + n data alone (rather than also including the 4He + p data). At r = 3.3 fm the values obtained for the P1/2 and P3/2 resonances are, respectively, Ec.m. = 1.97 and 0.77 MeV, Γc.m. = 5.22 and 0.64 MeV (1977BO24). See also (1982FR11; theor.).

See also (1978TA1A, 1978TH1A, 1979FO16, 1979KA17, 1979LE1B, 1980DM1A, 1980FU1G, 1980LA20, 1980PE1K, 1980VI01, 1981FR20, 1982AV02, 1982AZ01, 1982FR14, 1982LE1G, 1982OR03; theor.).

7. 4He(n, d)3H Qm = -17.5894 Eb = -0.89

For a study of the polarization at Epol. n = 50 MeV see (1982SA05). See also (1979AJ01) and reaction 7 in 5Li.

8. 4He(p, π+)5He Qm = -141.24

See (1981WI1F, 1982LE1L).

9. (a) 4He(d, p)5He Qm = -3.11
(b) 4He(d, pn)4He Qm = -2.2246

A typical proton spectrum consists of a peak corresponding to formation of the ground state of 5He, plus a lower continuum of protons ascribed to deuteron breakup (reaction (b)). Ground-state protons show pronounced azimuthal asymmetry when the reaction is induced by 8.5, 10 and 11 MeV vector polarized deuterons. Reaction (b) has been studied for E = 6.8 to 165 MeV: see (1979AJ01). See also 6Li.

At Eα = 70 MeV, a kinematically complete experiment (reaction (b)) shows evidence for sequential decay, proceeding through excited states of 5He. Peaks in the coincident yield of protons and deuterons are ascribed to narrow states at Ex = 16.7 ± 0.1 MeV, Γ = 80 ± 30 keV, at Ex = 18.6 ± 0.1, 18.8 ± 0.1 and 19.2 ± 0.1 MeV, all with Γ = 180 ± 60 keV (1973TR04). The fine structure near 19 MeV is not confirmed in other experiments [see, however, reaction 13]. Polarization studies are reported at Epol. d = 12 and 17 MeV (1983SL01), 12.0 and 21 MeV (1982IS06) and at 18 MeV (1981OS02). See also reaction 5 in 6Li, (1980BR20, 1980BR28, 1982LA14) and (1978NA12, 1980KO04; theor.).

10. 4He(t, nd)4He Qm = -6.2573

The results displayed in (1979AJ01) have not been published.

11. 6Li(γ, p)5He Qm = -4.59

At Eγ = 60 MeV, the proton spectrum shows two prominent peaks attributed to 5He*(0 + 4.0, 20 ± 2) (1976MA34). See also (1979AJ01) and 6Li.

12. 6Li(e, ep)5He Qm = -4.59

At Ee = 1180 MeV, the exciation of 5He*(0, 16.7) is reported: the latter state is formed with the ejection of an s-proton: see (1979AJ01) and reaction 5 in 6Li.

13. (a) 6Li(n, d)5He Qm = -2.37
(b) 6Li(n, nd)4He Qm = -1.4753

Angular distributions of ground-state deuterons have been studied at En = 6.57, 6.77, 14.4 and 56.3 MeV and recently at 14.1 MeV (1982HI06). At En = 56.3 MeV angular distributions have also been obtained to 5He*(16.7, 18.5 ± 0.5, 20.5 ± 0.5). The observation of the two highest states is not certain: if they exist their widths are less than the instrumental width, 1.6 MeV (1977BR17). See also (1974AJ01, 1979AJ01).

14. 6Li(p, 2p)5He Qm = -4.59

At Ep = 100 MeV the population of 5He*(0, 16.7) and possibly of a broad structure at Ex ≈ 19 MeV is observed: momentum distributions for 5He*(0, 16.7) and angular correlation measurements are also reported. The main features of the data are reasonably well described by DWIA: see (1974AJ01, 1979AJ01). See also (1981PA25, 1982GO1H).

15. (a) 6Li(d, 3He)5He Qm = 0.90
(b) 6Li(d, n3He)4He Qm = 1.794

5Heg.s. has been observed in reaction (a) at Ed = 14.5 MeV: see (1979AJ01) [the Ed = 80 MeV work has not been published]. For reaction (b) see (1979HO04) and 8Be.

16. 6Li(α, αp)5He Qm = -4.59

At Eα = 140 MeV, 5He*(0, 20.0) are populated: DWIA calculations provide a good fit to the data (1979NA06). See also (1979AJ01).

17. 7Li(γ, d)5He Qm = -9.62

Differential cross sections have been measured at Eγ = 100 and 150 MeV to 5He*(0, 4.0) by (1982KIZW).

18. (a) 7Li(π+, 2p)5He Qm = 128.51
(b) 7Li(π-, 2n)5He Qm = 126.95

Reaction (a) shows broad structures attributed to the ground state of 5He, to the excited state at 4 MeV (1981WHZZ) and to p-1s-1 and s-2 states at ≈ 20 and (≈ 35) MeV excitation: see (1979AJ01). For reaction (b) see (1977BA1M).

19. (a) 7Li(n, t)5He Qm = -3.36
(b) 7Li(n, tn)4He Qm = -2.468

The angular distribution of t0 has been measured at Et = 14.4 MeV. Reaction (b) at the same energy involves 7Li*(4.63) and 5Heg.s.: see (1979AJ01) and 8Li. See also (1979BE1K; theor.).

20. (a) 7Li(p, 3He)5He Qm = -4.12
(b) 7Li(p, pd)5He Qm = -9.62

At Ep = 43.7 MeV, angukar distributions of the 3He groups to the ground state of 5He (Γ = 0.80 ± 0.04 MeV; L = 0 + 2) and to levels at 16.7 MeV (L = 1) and 19.9 ± 0.4 MeV (Γ = 2.7 MeV) have been studied. Since no transitions are observed in the 7Li(p, t)5Li reaction to the analogue 20 MeV state in 5Li [see 5Li], the transition is presumably S-forbidden and the states in 5He - 5Li near 20 MeV are 4D3/2 or 4D5/2 [compare 3H(d, d)]. Particle-particle coincidence data have been obtained at Ep = 43.7 MeV. They suggest the existence of 5He*(20.0) with Γ = 3.0 ± 0.6 MeV and of a broad state at ≈ 25 MeV. No T = 3/2 states decaying via T = 1 states in 4He were observed: see (1979AJ01). In reaction (b) (1981ER10; 670 MeV), 5He*(0 + 4, 16.7, 25) appear to be involved.

21. (a) 7Li(d, α)5He Qm = 14.23
(b) 7Li(d, n)4He4He Qm = 15.121

At Ed = 24 MeV, the α-particle spectrum from reaction (a) shows structures corresponding to the ground and 16.7 MeV states and to states at Ex ≈ 20.2 and 23.8 MeV with Γ ≈ 2 MeV and ≈ 1 MeV respectively: see (1979AJ01). See also (1977RO1C).

Reaction (b) proceeds mainly via excited states of 8Be and 5Heg.s.. Spectra suggest the involvement of the P1/2 state: the values suggested are inconsistent with each other because of the difficulty of evaluating the contribution to other reactions: see (1974AJ01) for the earlier values and see (1976FO21) for a discussion of some of the problems involved in these. (1976FO21) suggest a width for 5Heg.s. = 0.6 MeV and Ex = 4.1 ± 0.2, Γc.m. = 4.4 ± 0.2 MeV for the P1/2 state. See also (1980NE1B, 1982LA21), and 7Li, 8Be and 9Be.

22. (a) 9Be(p, pα)5He Qm = -2.46
(b) 9Be(p, d3He)5He Qm = -20.82

Reaction (a) has been studied for Ep = 26.0 to 100 MeV [see (1979AJ01)] and at 101.5 MeV (1980NA09). Reaction (b) has also been studied at the latter energy. DWIA calculations show that the reactions are dominated by quasifree processes (1980NA09). The continuum has been studied by (1983DE14) at Ep = 30, 50 and 75 MeV. See also 9Be.

23. 9Be(3He, 7Be)5He Qm = -0.88

The continuum has been studied by (1983DE14, 1981DE1X; E(3He) = 45 MeV): the ground state is also strongly populated.

24. (a) 9Be(α, 2α)5He Qm = -2.46
(b) 9Be(α, 8Be)5He Qm = -2.56

Reaction (a) has been studied at Eα = 28 to 37.4 MeV [see (1974AJ01)] and at 18 MeV (1980ZH1A). Reaction (b) has been studied at Eα = 65 MeV: only 5Heg.s. is observed for Ex ≤ 25 MeV (1976WO11). See also (1981BA20; theor.).

25. 10B(d, 7Be)5He Qm = -1.97

See (1982DO1E).

26. 11B(d, n)4He4He4He Qm = 6.4568

At Ed = 3.8 to 12 MeV this reaction involves 5Heg.s. and states in 8Be, 9Be and 12C: see (1979AJ01).