A=5He (1984AJ01)

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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 E_x ≈ 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 Q_m = 16.70

At low energies the reaction is dominated by a resonance at E_d = 107 keV; the mirror reaction shows resonance at E_d = 430 keV. The cross section for emission of 16.7 MeV γ-rays for E_d = 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 Γ_γ = 14 ± 4 eV, where Γ_n is taken as 66 keV. The cross sections derived from thick target yields from E_d = 150 to 1300 keV are analyzed into resonant and direct-capture contributions: there is disagreement about the cross section at resonance: see (1979AJ01). At E_d = 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 Q_m = 17.5894 E_b = 16.70
(b) ³H(d, 2n)³He Q_m = -2.9883
(c) ³H(d, pn)³H Q_m = -2.2246

Below E_d = 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 E_d = 107 keV: see Table 5.2 (in PDF or PS). From E_d = 10 to 500 keV, the cross section is well fitted with the assumption of s-wave formation of a J^π = 3/2⁺ state. Excitation curves and angular distributions for reaction (a) have been measured from E_d = 8 keV to 21 MeV and at E_t = 20.00 MeV [see (1974AJ01, 1979AJ01) for the earlier references] and at E_t = 12.5 to 117 keV (1983BR1G; σ_t), 7.49 to 16.65 MeV (0° excitation function; ± 1.0 → 4.4%) and E_d = 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 E_d = 0.2 to 1.0 MeV indicates intervention of the s-wave, J^π = 1/2⁺ channel, as well as possible p-waves above E_d = 0.3 MeV. At higher energies, the neutron polarization P₁(θ₁) 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 E_d = 5 to 15 MeV and, with deuterium as target, for E_t = 4.5 to 19.5 MeV (neutrons near 135° lab). The polarization increases monotonically from 0.03 at E_d = 3 MeV to ≈ 0.5 at E_d = 6.5 MeV and then with a lower slope to 0.69 at E_d = 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 E_d = 6 MeV, but then the proton polarization becomes ≈ 15% higher, converging back to the neutron values at E_d ≈ 12 - 13 MeV. This may be due to experimental factors (1971MU04). The tensor analyzing power of A_zz(0°) has been measured for E_{pol. d} = 0.24 to 6.75 MeV: large differences in A_zz(0°) for this reaction and for ³He(d, p) are reported for E_{pol. d} < 1.65 and > 4 MeV (1980DR01). See however (1980GR14). See also (1981CL1B, 1981DE2E; prelim.). For other polarization studies see (1974AJ01, 1979AJ01) and (1982SA05: E_d = 37.1 MeV).

(1981JA1F) suggests that errors of as much as 50% are possible in the reactivity values for E_d = 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 E_d = 8.3 to 78.1 keV.

Reaction (b) has been studied for E_d = 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 E_c.m. = 2.9 ± 0.3 MeV [E_x = 19.6 MeV], Γ_c.m. = 1.9 ± 0.2 MeV, consistent with J^π = 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 E_b = 16.70

The elastic scattering has been studied for E_d = 2.6 to 11.0 MeV [see (1979AJ01)] and at E_t = 0.6 to 3.4 MeV (1979KA33). The excitation curves show an interference at E_x ≈ 19 MeV and a broad (Γ > 1 MeV) resonance corresponding to E_x = 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 D_3/2 or D_5/2 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 E_d = 3.2 to 12.3 MeV show resonance-like behavior in the vector analyzing power near E_d = 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 E_x ≈ 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 Q_m = 10.44
(b) ³H(t, 2n)⁴He Q_m = 11.3322

At E_t = 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 E_x ≈ 2 MeV, Γ ≈ 2.4 MeV: see (1979AJ01). For reaction (b), see ⁶He.

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

Some evidence is reported at E_t = 22.25 MeV in reaction (a) for a broad state of ⁵He at E_x ≈ 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 E_b = -0.89

The coherent scattering length (thermal, bound) is 3.07 ± 0.02 fm, pol. σ_s = 0.76 ± 0.01 b (1981MUZQ). Total cross sections for E_n = 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; E_n = 50.4 MeV).

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

The P_3/2 phase shift shows strong resonance behavior near 1 MeV, while the P_1/2 shift changes more slowly, indicating a broad P_1/2 level at several MeV excitation. (1966HO07) have constructed a set of phase shifts for E_n = 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 E_res = 17.669 MeV ± 10 keV, γ²_d = 2.0 MeV ± 25%, γ²_n = 50 keV ± 25% (see Table 5.2 (in PDF or PS)). The work of (1976LI15) indicates some discepancies with the results of (1966HO07) [below E_n = 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 P_1/2 and P_3/2 resonances are, respectively, E_c.m. = 1.97 and 0.77 MeV, Γ_c.m. = 5.22 and 0.64 MeV (1977BO24). See also (1982FR11; theor.).

7. ⁴He(n, d)³H Q_m = -17.5894 E_b = -0.89

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

8. ⁴He(p, π⁺)⁵He Q_m = -141.24

See (1981WI1F, 1982LE1L).

9. (a) ⁴He(d, p)⁵He Q_m = -3.11
(b) ⁴He(d, pn)⁴He Q_m = -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 E_α = 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 E_x = 16.7 ± 0.1 MeV, Γ = 80 ± 30 keV, at E_x = 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 E_{pol. 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 Q_m = -6.2573

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

11. ⁶Li(γ, p)⁵He Q_m = -4.59

At E_γ = 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 Q_m = -4.59

At E_e = 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 Q_m = -2.37
(b) ⁶Li(n, nd)⁴He Q_m = -1.4753

Angular distributions of ground-state deuterons have been studied at E_n = 6.57, 6.77, 14.4 and 56.3 MeV and recently at 14.1 MeV (1982HI06). At E_n = 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 Q_m = -4.59

At E_p = 100 MeV the population of ⁵He*(0, 16.7) and possibly of a broad structure at E_x ≈ 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 Q_m = 0.90
(b) ⁶Li(d, n³He)⁴He Q_m = 1.794

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

16. ⁶Li(α, αp)⁵He Q_m = -4.59

At E_α = 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 Q_m = -9.62

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

18. (a) ⁷Li(π⁺, 2p)⁵He Q_m = 128.51
(b) ⁷Li(π^-, 2n)⁵He Q_m = 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 Q_m = -3.36
(b) ⁷Li(n, tn)⁴He Q_m = -2.468

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

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

At E_p = 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 ⁴D_3/2 or ⁴D_5/2 [compare ³H(d, d)]. Particle-particle coincidence data have been obtained at E_p = 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 Q_m = 14.23
(b) ⁷Li(d, n)⁴He⁴He Q_m = 15.121

At E_d = 24 MeV, the α-particle spectrum from reaction (a) shows structures corresponding to the ground and 16.7 MeV states and to states at E_x ≈ 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 ⁵He_g.s.. Spectra suggest the involvement of the P_1/2 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 ⁵He_g.s. = 0.6 MeV and E_x = 4.1 ± 0.2, Γ_c.m. = 4.4 ± 0.2 MeV for the P_1/2 state. See also (1980NE1B, 1982LA21), and ⁷Li, ⁸Be and ⁹Be.

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

Reaction (a) has been studied for E_p = 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 E_p = 30, 50 and 75 MeV. See also ⁹Be.

23. ⁹Be(³He, ⁷Be)⁵He Q_m = -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 Q_m = -2.46
(b) ⁹Be(α, ⁸Be)⁵He Q_m = -2.56

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

25. ¹⁰B(d, ⁷Be)⁵He Q_m = -1.97

See (1982DO1E).

26. ¹¹B(d, n)⁴He⁴He⁴He Q_m = 6.4568

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