(See Energy Level Diagrams for 5He)
GENERAL: References to articles on general properties of 5He published since the previous review (1988AJ01) are grouped into categories and listed, along with brief descriptions of each item, in the General Tables for 5He located on our website at (nucldata.tunl.duke.edu/NuclData/General_Tables/5he.shtml).
See also the A = 5 introductory discussion titled A = 5 resonance parameters.
The quasi-free neutron knockout reaction was studied with 6He beams produced by 115 MeV 15N primary beams (1997KOZV, 1997KO07). 5He was observed in the separation energy spectra. The 5He → 4He + n decay energy is reported to be consistent with the "known mass of 5He" and is given as 0.97 MeV.
At low energies the reaction is dominated by a resonance at Ed = 107 keV; the mirror reaction shows resonance at Ed = 430 keV. The branching ratio Γγ0/Γn integrated over the resonance from 0 to 275 keV is (5.6 ± 0.6) × 10-5 (1986MO05), in very good agreement with the earlier value of (5.4 ± 1.3) × 10-5 for Ed = 45 to 146 keV (1984CE08). Assuming Γn of 5He*(16.7) is 37 ± 5 keV (see reaction 8), then Γγ0 = 2.1 ± 0.4 eV. (1986MO05) also report branching ratios up to Ed = 0.72 MeV and summarize the earlier work to 5 MeV. More recently, a measurement (1993KA01) at Ed = 100 keV of the 3H(d, γ)5He/3H(d, α)n ratio gave (1.2 ± 0.3) × 10-4 which is larger than the results of (1986MO05) and (1984CE08) but includes contribution from decay to both the ground and first excited states.
Differential cross sections, vector- and tensor-analyzing powers were measured at Ed = 400 keV for 3H(d, γ)5He (1989RI04) and at Ed = 0.1, 0.45 and 8.6 MeV for 3H(d, γ) and 3He(d, γ) by (1994BA02). These results were compared with coupled channels resonating group model (CCRGM) calculations. See also the shell model description of the 3/2+ resonance presented in (1993KU02).
The 3H(d, γ)5He and 3He(d, γ)5Li reactions were used in a measurement (1991BA02) of the ground state widths of 5He and 5Li. The results were Γn = 1.36 ± 0.19 MeV in 5He and Γp = 2.44 ± 0.21 MeV for 5Li. These values lead to reduced widths for 5He and 5Li which are equal (within error). This is consistent with charge symmetry expectations. The ground-state widths given by the conventional R-matrix prescription in 5.2 (in PDF or PS) and 5.4 (in PDF or PS) are 0.963 MeV and 2.11 MeV for 5He and 5Li, respectively.
The data of (1991BA02) were used by (1996EF03) in a single-level R-matrix analysis to obtain values of the ground-state energies and widths of 5He and 5Li, close to those given by the extended R-matrix prescription in 5.1 (in PDF or PS) and 5.3 (in PDF or PS).
The cross section for reaction (a) has been measured in the range Et = 12.5 to 117 keV (1984JA08) [0.525(± 4.8%) mb to 3.739(± 1.4%) b] and in the range Ed = 79.913 to 115.901 keV (± 0.015 keV) (1987BR10) [3.849 to 4.734 b (± 1.6%)]. See also (1985FI1G; Ed = 13.8 to 114.3 keV). A strong resonance, σ (peak) = 4.88 b, appears at Ed = 105 keV: see 5.2 (in PDF or PS) in (1979AJ01) and (1987BR10). For a discussion of R-matrix analysis and evidence for a "shadow" pole, see (1987BR10, 1987HA20). See also (1987HA44, 1987MO1K). The related work of (1991BO23) uses a resonance coupled channels model to interpret the 5He (3/2+) resonance as a coupled channel pole associated predominantly with the d-t system. A later study by (1993CS02) uses a realistic dynamical microscopic reaction approach and reaches the same conclusion. A more recent analysis of cross section data for Ed = 8 - 116 keV is described in (1995LA33). Resonance parameters for the 5He 3/2+ second excited state were determined.
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. (See however the discussion below.) Measurements of cross sections and angular distributions for reaction (a) have been reported to Ed = 21 MeV and Et = 20.0 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)] as well as at 1.0, 1.5 and 2.0 MeV (1987LI07). Neutron yields from reaction (a) above have been measured at Ed = 140 - 300 keV (1989SH17). Measurements to determine the intensity of intermediate energy neutrons are described in (1989GA21). An absolute measurement of the polarization of 50 MeV neutrons at θlab = 29.7° was reported in (1991SA18).
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. 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 cm 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. Vector polarization transfer coefficients, Kyy'(0°) have been measured for Ed = 5 to 11 MeV (1985HOZU, 1986HO1E). For earlier polarization work see (1984AJ01).
An R-matrix formalism was used in a phase shift analysis of d + 3H below 1 MeV to obtain the contribution of 2S1/2- and P-wave channels near the 5He (3/2+) resonance. See also the recent work (1997BA72) in which properties of the 3/2+ levels of 5He and 5Li are discussed in terms of conventional R-matrix parameters. The multichannel resonating group model has been used in a study (1990BL08) of partial wave contributions in this energy region.
Improved formulae for fusion cross sections and thermal reactivities utilizing new data and R-matrix techniques are presented in (1992BO47). See also (1989AB21, 1989SC1F, 1989SC19, 1989SC25, 1989SC41).
The 3H(d, n) reactivity in fusion reactors and screening-effect corrections needed for low energy data are discussed in (1989LA29).
(1987BR10) have derived astrophysical S-factors in the range Ed = 8.3 to 115.9 keV [S(0) = 11.71 ± 0.08 MeV · b], as well as reactivities. See (1984AJ01) for the earlier work, and (1985CA41, 1987VA36). Angular distributions of α particles were measured for Ed < 200 keV (1997BE59) and evidence for a D-wave contribution to the cross section in the vacinity of the 3/2+ s-wave resonance in 5He was reported. Thermonuclear reaction rates for this reaction calculated from evaluated data are presented in the compilation (1999AN35).
Reaction (b) has been studied for Ed = 10.9 to 83 MeV. A study of reaction (c) leads to the suggestion of a resonance at Ecm = 2.9 ± 0.3 MeV [Ex = 19.7 MeV], Γcm = 1.9 ± 0.2 MeV, consistent with Jπ = 3/2- [see 5.1 (in PDF or PS)]: see (1974AJ01, 1979AJ01). See also the references cited in (1988AJ01). For applications and developments in muon-catalyzed fusion see the references cited in (1988AJ01) and the General Table for 5He located on our website at (nucldata.tunl.duke.edu/NuclData/General_Tables/5he.shtml).
The elastic scattering has been studied for Ed = 2.6 to 11.0 MeV: see (1984AJ01). For earlier measurements at other energies see (1966LA04). 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 ≈ 19.7 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). Elastic scattering data is also utilized in the S-matrix studies of the 5He (3/2+) resonance at Ex = 16.84 MeV (1988BE1U, 1991BO23, 1993CS02). (See reaction 3). See also the effective-range expansion and Coulomb renormalization for d + t and related systems (1991KA31, 1996PO26). For earlier references see (1979AJ01, 1988AJ01). For d-t correlations see (1987PO03). See also "Complex reactions" in the General section of (1988AJ01) and (1981PL1A, 1983HAYX, 1986BO01). See also (1997BA72) in which properties of the 3/2+ levels of 5He and 5Li are discussed in terms of conventional R-matrix parameters.
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 5Heg.s.; (iii) sequential decay via a broad excited state of 5He. The width of 5Heg.s. 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). See also 6He and (1986BA73).
A kinematically complete experiment at Eα = 67.2 MeV has been reported by (2000GO35). They report observation of 5He excited states at Ex = 18.9, 19.9 and 20.7 MeV with widths of 0.3, 0.25 and 0.25 MeV, respectively.
The coherent scattering length (thermal, bound) is 3.07 ± 0.02 fm, σs-bar = 0.76 ± 0.01 b. Total cross sections have been measured for En = 4 × 10-4 eV to 150.9 MeV and at 10 GeV/c [see (1984AJ01)] and at En = 1.5 to 40 MeV (1983HA20).
The total cross section has a peak of 7.6 b at En = 1.15 ± 0.05 MeV, Ecm = 0.92 ± 0.04 MeV, with a width of about 1.2 MeV: see (1979AJ01). A second resonance is observed at En = 22.133 ± 0.010 MeV [σpeak = 0.9 b] with a total width of 76 ± 12 keV and Γn = 37 ± 5 keV (1983HA20). Attempts to detect additional resonances in the total cross section have been unsuccessful: see (1979AJ01). For curves and tables of neutron cross sections see (1988MCZT, 1990NAZH, 1990SH1C).
The P3/2 phase shift shows strong resonance behavior near 1 MeV, while the P1/2 phase 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, γd2 = 2.0 MeV ± 25%, γn2 = 50 keV ± 20% (see 5.2 (in PDF or PS) in (1979AJ01)). See also (1997BA72) in which properties of the 3/2+ levels of 5He and 5Li are discussed in terms of conventional R-matrix parameters.
An R-function analysis of the 4He + n data below 21 MeV (including absolute neutron analyzing power measurement and accurate cross section measurements) 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 a = 3.3 fm the values obtained for the P1/2 and P3/2 resonances are, respectively, Ecm = 1.97 and 0.77 MeV, Γcm = 5.22 and 0.64 MeV: see (1984AJ01). Angular distributions of Ay have been studied by (1984KL05, 1984KR23, 1986KL04) for En = 15 to 50 MeV: see also for phase-shift analysis and comparison with 4He(p, p).
The excitation energies and the spectroscopic factors for 5He states are obtained by (1985BA68) from 2-level R-matrix fits to the phase shifts, as functions of the channel radius. For a ≈ 5.1 fm a very broad state with Jπ = 1/2+ is found to lie at Ex ≈ 7 MeV in both 5He and 5Li, in agreement with the shell-model calculation by (1984VA06). Broad 3/2+ and 5/2+ states then lie at ≈ 14 MeV and the 1/2- state is at about 2.6 MeV. (1985BA68) suggest that the phase-shift analysis should be redone with values of a larger than those previously used (a ≈ 3 fm). See also references cited in (1988AJ01). In more recent work S-matrix studies of the low energy 3/2- and 1/2- states are described in (1997CS01, 1998CS02). See also the calculations of (1999AO01, 1999FI10).
Nucleon-α potentials have been derived from phase shifts by (1991CO05) and constructed from experimental data by the Marchenko inversion method as discussed in (1993HO09). The scattering amplitude in the vicinity of the 5He (3/2+) resonance is expressed in terms of the scattering length and the d-t effective range by (1994MU07). A study of the two-pole structure of the 3/2+ resonance is discussed in (1993CS02). See also the discussion of Pauli blocking in this reaction (1990AM07) and an application of an algebraic cluster approach to n-α scattering (1989US02).
More recently differential cross sections and analyzing powers were measured at incident proton energies between 240 and 507 MeV, spanning the region of the Δ1232 resonance (1994FU06). These results were compared with the prediction of a microscopic (p, π+) model and with a phenomenological model. See (1994FA10).
A typical proton spectrum (reaction (a)) consists of a peak corresponding to the formation of the ground state of 5He, plus a continuum of protons ascribed to reaction (b). A study of the latter reaction shows evidence for sequential decay via 5He*(0, 16.7 ± 0.1 [Γ = 80 ± 30 keV]) and suggests some fine structure near Ex = 19 MeV [see also reactions 15 and 23]: see (1979AJ01). Differential cross sections and VAP have been measured for the ground state group at Ed = 5.4, 6.0, and 6.8 MeV (1985LU08) and at 6 to 11 MeV (1985OS02). Measurements of differential cross sections, analyzing powers, and polarization transfer coefficients at Ed = 56 MeV were reported in (1990YOZZ). At Eα = 28.3 MeV tensor polarization measurements involving the ground state transitions to 5He (and 5Li) deviate from theoretical predictions which assume charge symmetry (1985WI15). See also 6Li (1988PUZZ; Ed = 2.1 GeV) and other references cited in (1988AJ01).
Cross sections and transverse tensor analyzing powers for reaction (b) at Ed = 7 MeV were measured with kinematic conditions chosen to correspond to singlet deuteron production (1988GA14).
Theoretical studies relevant to reaction (b) include: a study of effects of the proton Coulomb field on α, n resonance peaks (1988KA38); comparisons of measured cross sections and polarization observables at Ed = 12, 17 MeV with a three-body model (1988SU12); a study of the influence of three-particle Coulomb dynamics on the cross section (1991AS02); a study of the effects of the internal structure of the α particle on the reaction (1990KU27); and a multiconfiguration resonating group study of the six-nucleon system (1991FU01, 1995FU16).
Differential cross sections for this reaction to 5Heg.s. were measured at E(4He) = 118 MeV, and compared with DWBA predictions (1994WA06). Measurements of angular distributions at Eα = 158 and 200 MeV were reported by (1996ST25).
A study of this reaction and of the 4He(7Li, 6He)5Li reaction at E(7Li) = 50 MeV, and of the 6Li(12C, 13N)5He and 6Li(13C, 14C)5Li reactions at E(C) = 90 MeV was reported by (1988WO10). Properties of the two lowest states of 5He and 5Li, from R-matrix parameters (a = 5.5 fm) are displayed in 5.2 (in PDF or PS) of (1988AJ01). As noted there, positive parity states are then predicted to lie at Ex ≈ 5 MeV (1/2+) and 12 MeV (3/2+, 5/2+) in 5He - 5Li (1988WO10). See also the analysis in (1988BA75).
At Eγ = 60 MeV, the proton spectrum shows two prominent peaks. In early work cited in (1979AJ01) these peaks are attributed to 5He*(0 + 4.0, 20 ± 2): see (1979AJ01). The (γ, p0+1) cross section has been reported for Eγ = 34.5 to 98.8 MeV. A broad secondary structure is also observed (1988CA11). A review of photodisintegration data for energies up to Eγ = 50 MeV was presented in (1990VA16). More recently, measurements were made at Eγ = 60 MeV (1994RY01), at Eγ = 61, 77 MeV (1994NI04), and at Eγ = 59 - 75 MeV (1995DI01). In reaction (b) the missing energy spectrum shows strong peaks due to 5He*(0, 16.7) and possibly some strength in the region Ex = 5 - 15 MeV (1986LAZH). See also 6Li, and see the recent triple cross section measurements of (1999HO02). Reviews of (e, e'p) data are presented in (1990DE16, 1991VA05). See also (1989LA13, 1990DE06, 1990LA06). A microscopic cluster model used to interpret these experiments is discussed in (1990LO14). For reaction (c) at Eπ+ = 130 and 150 MeV, 5He*(0, 16.7) are populated (1987HU02). Measurements at Eπ+ = 500 MeV were made by (1998PA31) to search for Δ components. Reaction (d) was studied at GeV energies by (2000AB25) to deduce Fermi momentum distributions.
Angular distributions of d0 have been studied at En = 6.6 to 56.3 MeV. At En = 56.3 MeV angular distributions have also been obtained to 5He*(16.7) and, possibly, to two higher states: see (1979AJ01, 1984AJ01). Measured cross sections and analysis for En = 14.1 MeV are presented in (1989SHZS). See also (1986BOZG). A Multiconfiguration Resonating-Group Method calculation applied to this reaction is discussed in (1995FU16).
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. Measurements were reported at Ep = 47 and 70 MeV (1983VD03), 70 MeV (1983GO06), 392 MeV (1996KAZZ, 1997HA15, 1998NO04), and 1 GeV (1985BE30, 1985DO16, 2000MI17). See also (1984AJ01). Experimental and theoretical studies for Ep = 30 - 150 MeV were reviewed in (1987VD1A). See also (1987VD01). The influence of noncoplanarity on information obtained from these reactions was studied by (1990GO34).
5Heg.s. has been observed at Ed = 14.5 MeV: see (1979AJ01).
At Eα = 140 MeV 5He*(0, 20.0) are populated: see (1984AJ01).
Angular distributions have been obtained at E(6Li) = 156 MeV to 5Heg.s.. Unresolved states at Ex = 16 - 20 MeV are also populated (1987MI34).
DWIA calculations of cross sections and analyzing powers for population of 5Heg.s.(3/2-) are described in (1992KH04).
At Ep = 43.7 MeV, angular 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 analog 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). Measurements of angular distributions at Ep = 29.1 - 44.6 MeV are reported in (1989BA88). In reaction (b) 5He*(0 + 4, 16.7, 25) appear to be involved at Ep = 670 MeV (1981ER10) while at 200 MeV some structure at Ex ≈ 20 MeV is reported in addition to the ground state (1986WA11).
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. Measurements of the α-particle energy spectra at Ed = 13.6 MeV were reported in (1993PAZP). An analysis of cross section data measured at Ed = 0 - 12 MeV is reported in (1997HAZX). Astrophysical S factors were measured at Ecm = 57 - 141 keV by (1997YA08). Measurements of the reaction rate at low energies for 7Li implanted in Pd foil were reported by (2000BAZO). Reaction (b) proceeds mainly via excited states of 8Be and 5Heg.s. and possibly as well 5He*(4.): see (1979AJ01). Measurements at Ed = 4.35 MeV have been reported by (2000MIZU). See also (1987WA21) and 8Be in (1988AJ01).
Measurements of σ(θ) at Ed = 6.8 MeV were reported in (1989AR04). Parameters of the resonance for the 5He state at Ex = 16.76 MeV were extracted. Analysis (1991AR10, 1993FA12) of coincidence measurements at Ed = 1.4, 2.1 and 2.5 MeV gave Ex = 4.1 ± 0.2 MeV, Γ = 2.9 ± 0.4 MeV for the 5He p1/2 first excited state.
A kinematically complete experiment is reported at E(3He) = 120 MeV. The cross section for reaction (b) is an order of magnitude greater than that for reaction (a). The missing mass spectrum for the composite of both reactions suggests the population of several states of 5He, in addition to 5He*(0, 16.7, 20.0), including a state at 35.7 ± 0.4 MeV with a width of ≈ 2 MeV (1985FR01).
Both reactions have been studied at Ep = 26.0 to 101.5 MeV [see (1984AJ01)]. Reaction (a) was studied at Ep = 150.5 MeV (1985WA13) and at Ep = 200 MeV (1989NA10), who analyzed the data in terms of DWIA. Absolute spectroscopic factors were derived. See also (1985VD03). More recently, cross sections and polarization observables were measured at Ep = 296 MeV by (1996YOZZ, 1997YOZQ, 1998YO09). Alpha spectroscopic factors were deduced.
Measurements at Eα = 197 MeV of energy-sharing distributions were reported by (1994CO16). Spectroscopic factors were extracted. See (1984AJ01) for earlier work. Cross section measurements at Eα = 580 MeV with DWIA calculations are described in (1999NA05).
Cross sections were measured and the mass excess was extracted by (1990BEYY).
An angular distribution has been measured at Ed = 13.6 MeV involving 5Heg.s. and 7Be*(0.43) (1983DO10).