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5He (1979AJ01)

(See Energy Level Diagrams for 5He)

GENERAL: See also (1974AJ01) and Table 5.1 [Table of Energy Levels] (in PDF or PS) here.

Model calculations: (1974JA30, 1974LE22, 1975DI04).

Special states: (1974GO13, 1974IR04, 1974JA30, 1974LE22, 1975DI04, 1976IR1B).

Special reactions: (1973FE1A, 1974FE1A, 1975FE1A, 1976VA29, 1978ME1C).

Reactions involving pions: (1973BA30, 1978FI1E).

Other topics: (1974GO13, 1974IR04, 1976BI1A, 1976IR1B, 1977SH1B, 1978GO1D).

Ground state of 5He: (1975BE31, 1977HI09).

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. (1969BE56) have measured the cross section for emission of 16.7 MeV γ-rays for Ed = 25 to 100 keV: 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. (1963BU07) have measured thick target yields from Ed = 150 to 1300 keV. The derived cross sections are analyzed into resonant and direct-capture contributions: the cross section at resonance is here reported as 60 μb [versus 1 mb reported by (1969BE56)]. At Ed = 1025 ± 47 keV, 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 (1970KO09). The cross section for γ0 has been measured (at 90°) for Ed = 2.0 to 12.0 MeV and angular distributions were obtained at Ed = 4, 8, 10 and 12 MeV for γ0 (1975BA1E; and C.A. Barnes, private communication). See also (1974AJ01).

2. (a) 3H(d, n)4He Qm = 17.5894 Eb = 16.70
(b) 3H(d, 2n)3He Qm = -2.9884
(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(-44.40 E-1/2) (1953JA1A, 1954AR02). 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 (1952AR30, 1952CO35, 1955KU03). Excitation curves and angular distributions for reaction (a) have been measured from Ed = 8 keV to 21 MeV: see (1974AJ01) for earlier references and (1976DR1A, 1976DR1B; preliminary work; angular distributions at Ed = 7.00 and 10.00 MeV, 13.36 and 16.50 MeV (partial) and at Et = 10.48 and 14.98 MeV; 0° excitation function for Ed = 7 to 16.5 MeV), (1975MA28; angular distributions at Ed = 8 to 16 MeV, in 1 MeV steps; 0° excitation function for same interval) and (1977JA07; dσ/dΩ at Et = 20.00 MeV; very accurate).

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 (1965TR01, 1971GR32). 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). Using polarized deuterons (1971HI07) find that the average ratio of vector analyzing power of 3He(d, p) to 3H(d, n) is 1.016 ± 0.015 at Ed = 6 MeV and 1.035 ± 0.020 at 10 MeV. The vector analyzing power of the two reactions agree to within ± 0.025 at all angles. This agreement between the mirror reactions is in apparent conflict with the result of (1971MU04). For earlier polarization measurements see Table 5.3 (in PDF or PS) in (1974AJ01). Polarization studies are also reported by (1976SU06; Ed = 7 MeV), (1976LI15; Ed = 3.5 to 12.8 MeV), (1976OH02; Epol. t = 5.37 to 10.50 MeV) and (1975SA1A; preliminary; Ed = 38 MeV; looked at pol. of 50 MeV neutrons). See also (1977DR1B). The Ky'y(0°) determined for Epol. t = 5.37 to 10.50 MeV show a minimum at Epol. t = 9.6 MeV (1976OH02). See also (1978CA13; Ed = 0.7 MeV).

Reaction (b) has been studied for Ed = 10.9 to 83 MeV: see (1974AJ01). A discussion and comparison of attempts to measure 1S0 nn scattering length is presented by (1971GR45; Ed = 13.4 MeV): based on kinematically complete measurements and using the Watson-Migdal treatment, they find ann = -16.0 ± 1.0 fm. Intervention of n - 3He final state interactions is believed to be small in this work (1971GR45). At Et = 22 MeV no clear evidence is seen for sequential processes via excited states of 4He (1971GR12).

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)]. n-p final-state interaction enhancement has been studied by (1973SL03) at Ed = 35 MeV. They find that only when Enp ≤ 1 MeV is in agreement with the Watson-Migdal theory obtained, even if data far from dominant n-t final-state interaction and p-t quasi-free scattering are chosen. See also (1974AL01).

See also (1974AD11), (1974GE1B, 1974WI1D, 1975CR1A, 1975ST1A, 1975ST1B, 1976BL1A, 1976BR1B, 1976JA1C, 1976MO1A, 1977BE1H, 1977KI1C, 1977MC1C; applied topics), (1973LI1B, 1975KU1C, 1975SE07, 1975SO1C, 1976HA1C, 1976SE1B, 1976WA1C, 1977SE09; reviews), (1975FO19; astrophysics) and (1974KE1B, 1974ST14, 1975DO1B; theor.).

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

The elastic scattering has been studied for Ed = 2.6 to 11.0 MeV. 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 (1967TO02, 1968IV01) [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-bar = 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) (1971KI02). Tensor analyzing powers have been measured for Ed = 5.0 to 11.5 MeV (1973DE51), at Epol. t = 10.5 MeV (1976OH02) and at Ed-bar = 11.4 and 14.4 MeV (1974DO05; angular distributions of tensor and vector polarizations). See also (1974ST14, 1975AB1C, 1975DO1B, 1976BA1E; theor.).

4. (a) 3H(t, n)5He Qm = 10.44
(b) 3H(t, 2n)4He Qm = 11.3321

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 branching ratios at θ = 90° are 0.7 : 0.2 : 0.1. 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 (1965WO03). For reaction (b), see 6He and (1974LA02).

5. (a) 3He(t, p)5He Qm = 11.20
(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) (1968YO06). For reaction (b) see 6Li and (1975SC28, 1977DEYM).

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

The coherent scattering length (thermal, bound) is 3.0 ± 0.1 fm (1973MU14). The thermal scattering cross section is 0.773 ± 0.009 b and the absorption cross section at 2200 m/sec σn,γ0 is < 0.05 b (1969RO16). (1973MU14) adopt 0.76 ± 0.01 b for σs-bar. Total cross sections for En = 4 × 10-4 eV to 150.9 MeV and at 10 GeV/c are summarized in (1974AJ01, 1976GAYV). Angular distribution measurements are summarized in (1970GA1A, 1974AJ01). Polarization studies are displayed in Table 5.4 (in PDF or PS) of (1974AJ01): recent work includes that of (1976BO05: En = 1.5 to 6.0 MeV; used an absolutely calibrated source of polarized neutrons), (1976LI15: En = 20 to 30 MeV; Ay(θ) is the same for 4He + n and 4He + p) and (1978YO1A: En-bar = 50 MeV). See also (1974TO03).

The total cross section has a peak of 7.6 b (1973GO38) at En = 1.15 ± 0.05 MeV, Ec.m. = 0.92 ± 0.04 MeV, with a width of about 1.2 MeV (1964ST25). A second resonance is observed at En = 22.15 ± 0.12 MeV, corresponding to the 16.7 MeV Jπ = 3/2+ state (1959BO54, 1964SH30): Γc.m. = 100 ± 50 keV, Γn = Γd = 50 ± 35 keV (1960HU08). [(1966HO07) find that the data are fitted best by Γn < Γd although Γn < Γd is not excluded]. Attempts to detect 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 (1952DO30, 1966HO07, 1970AR1B, 1972ST01). (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. They have measured differential cross sections from 6 to 30 MeV, with special attention to the region near 22.15 MeV and have fitted the data with the assumed 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 polarization has been calculated from the phase shifts and is presented as a contour plot (1966HO07). The work of (1976LI15) indicates some discrepancies with the results of (1966HO07) [below En = 22 MeV] and with the measurements of (1972BR10).

A recent 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 (1974KR07). For earlier analyses, see (1974AJ01). See also (1974MA1C, 1977YO1B), (1975FI1B, 1976OH1B, 1976WA1B, 1976WA1C) and (1974BA34, 1974DO10, 1974GH01, 1974JA1F, 1974ST14, 1975BA76, 1975CA05, 1975LO1A, 1975TH12, 1976AH1A, 1976AL1E, 1976CH1B, 1976SP1A, 1977BA1N, 1977BE50, 1977CH1C, 1977LA1C, 1977LE1D, 1977PH01, 1977ST1D, 1977TH09, 1978AH01, 1978FO1G, 1978FR02, 1978KO13, 1978LE1H, 1978MA37; theor.).

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

See (1976BR1B), (1974AJ01) and (1976BA1E; theor.).

8. (a) 4He(d, p)5He Qm = -3.12
(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. A DWBA calculation is in only qualitative agreement (1967TR05, 1971KE16).

Reaction (b) has been studied for E = 9 to 165 MeV: see (1974AJ01) and Ed = 6.8 and 7.8 MeV (1978KA11), 8.9 MeV (1977SA21), at Ed-bar = 15 MeV (1978NA08), Eα = 21.9 and 23.7 MeV (1974RA10), 22.5 MeV (1977PR06), 27.2 MeV (1974GR40) and 165 MeV (1974HO11). See also 6Li.

At Ed = 8.9 MeV, the FSI (final state interaction) is very important (1977SA21). In the kinematically complete experiment of (1977PR06) at Eα = 22.5 MeV, the results are in quite good agreement with the predictions of the sequential decay model: the slight deviations are assumed to be due to the omission of Coulomb interaction effects and to the restriction to partial waves with l ≤ 2. At Eα = 70 MeV, a kinematically complete experiment 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 12].

See also (1974HE21, 1974NA10, 1975HE09, 1976KO21, 1976LI1E, 1977BR25, 1978FI1E, 1978KO13), 5Li and 6Li.

9. 4He(t, nd)4He Qm = -0.4105

At Eα = 70 MeV, there is indication of the population of 5He*(0, 16.7) and of a structure with Ex = 18 - 20 MeV (1974LA1A, 1975AL1A; preliminary results).

10. 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) (1973GA16, 1976MA34). See also (1973DE17), (1975MA1E) and 6Li.

11. 6Li(e, ep)5He Qm = -4.59

At Ep = 1180 MeV, the exciation of 5He*(0, 16.7) is reported: the latter state is formed with the ejection of an s-proton (1972AN24, 1972AN27, 1972AN29). See also (1975ME27; theor.).

12. (a) 6Li(n, d)5He Qm = -2.37
(b) 6Li(n, nd)4He Qm = -1.4735

Angular distributions of ground state deuterons have been studied at En = 6.57 and 6.77 MeV (1977RO01), 14.4 MeV (1965VA05) and 56.3 MeV (1977BR17). In the latter experiment, 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). For reactrion (b) see (1967VA12). See also (1974AJ01).

13. 6Li(p, dπ+)5He Qm = -142. 72

See (1976HUZK).

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 (1974BH03). For the earlier work see (1974AJ01). See also (1975VO04, 1977RO1E) and (1974GH03, 1974PR10, 1975CH1C, 1976OH04; theor.).

15. (a) 6Li(d, 3He)5He Qm = 0.90
(b) 6Li(d, n3He)4He Qm = 1.795

At Ed = 14.5 MeV, 5Heg.s. is populated (1955LE24). At Ed = 80 MeV, the population of 5He*(16.7) as well as a broad state near Ex = 19 MeV is reported (1975DI1A, 1975DI1B; abstracts). For reaction (b) see (1974AJ01).

16. 6Li(t, α)5He Qm = 15.22

See (1974AJ01).

17. (a) 6Li(α, 5Li)4He + n Qm = -5.66
(b) 6Li(α, αp)5He Qm = -4.59

See (1975GR42) for reaction (a) and (1978CA1E) for reaction (b).

18. 7Li(γ, d)5He Qm = -9.62

See (1975DE37) in 7Li.

19. (a) 7Li(π+, 2p)5He Qm = 128.51
(b) 7Li(π-, 2n)5He Qm = 126.94

The two-proton spectrum shows broad structures attributed to the ground state of 5He, and to p-1s-1 and s-2 states at ≈ 20 and (≈ 35) MeV excitation (1965CH12). For reaction (b) see (1977BA1M).

20. (a) 7Li(n, t)5He Qm = -3.36
(b) 7Li(n, tn)4He Qm = -2.467

The angular distribution of the t0 group has been measured at Et = 14.4 MeV: it is fairly well reproduced by DWBA (1970MI05). Reaction (b) at En = 14.4 MeV proceeds as a sequential process primarily involving 7Li*(4.63) and 5Heg.s. (1974AN02). See also (1974TU1A) and (1974AJ01) for the earlier work.

21. (a) 7Li(p, 3He)5He Qm = -4.12
(b) 7Li(p, pd)5He Qm = -9.618

At Ep = 43.7 MeV, angular distributions of the 3He groups to the ground state of 5He (Γ = 0.80 ± 0.04 MeV) and to levels at 16.7 and 19.9 ± 0.4 MeV (Γ = 2.7 MeV) have been determined. The angular distribution of the 5He ground state group indicates substantial mixing of L = 0 and L = 2 transfer. The distribution to 5He*(16.7) is consistent with L = 1. 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)] (1966CE05). 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 (1968MC02). In reaction (b) at Ep = 100 MeV 5He*(0, 19.9) are strongly populated while 5He*(16.7) is very weak. Positive parity is suggested for 5He*(19.9) (1975CH1B; preliminary).

22. (a) 7Li(d, α)5He Qm = 14.23
(b) 7Li(d, n)4He4He Qm = 15.123

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 (1972BA30). The width of the ground state of 5He is 615 ± 30 keV (1973GA28). Angular distributions are reported for Ed = 0.6 to 1.25 MeV.

Spectra measured in reaction (b) suggest the involvement of the P1/2 state: the values suggested are inconsistent with each other because of the difficulty of evaluating the contribution of 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. Reaction (b) proceeds mainly via excited states of 8Be and 5Heg.s.: see, e.g., (1967VA11). See also (1973HU12, 1974DA28, 1974GR44, 1978AR10, 1978SP03). Attempts to observe n-α rescattering effects following formation of 8Be*(16.63, 16.91) have been unsuccessful: an upper limit of 1% of the yield from sequential decay is given by (1968VA12). See (1974AJ01) for more complete references to the older work. See also 8Be and 9Be.

23. 7Li(3He, d3He)5He Qm = -9.62

See (1976WA12).

24. 7Li(α, 6Li)4He + n Qm = -7.251

See (1975GR42).

25. 9Be(γ, α)5He Qm = -2.47

See 9Be.

26. 9Be(p, pα)5He Qm = -2.47

Studies of this reaction have been carried out at Ep = 26.0 to 57 MeV [see (1974AJ01)] and at Ep = 100 MeV (1977RO02). In the latter experiment good agreement is found with DWIA calculations: the average value of Sα = 0.45 ± 0.02 (1977RO02). See also 9Be.

27. 9Be(t, 7Li)5He Qm = 0.096

See (1975VO08).

28. 9Be(3He, α3He)5He Qm = -2.47

See 9Be.

29. (a) 9Be(α, 2α)5He Qm = -2.47
(b) 9Be(α, 8Be)5He Qm = -2.56

Reaction (a) has been studied at Eα = 28 to 37.4 MeV: see (1974AJ01). See also (1974GR42, 1977BR1E). Reaction (b) has been studied at Eα = 65 MeV: only the ground state of 5He is observed for Ex ≲ 25 MeV; Sα = 0.53 (1976WO11).

30. 11B(d, n)4He4He4He Qm = 6.4575

At Ed = 3.75 MeV (1978GR07), 10.4 and 12.0 MeV (1971RE19), this reaction involves 5Heg.s. and states in 8Be and 9Be (1971RE19, 1978GR07) and 12C (1978GR07).

31. 12C(n, n)4He4He4He Qm = -7.2748

See 12C in (1975AJ02).