(See Energy Level Diagrams for 7Be)
Nuclear models: (1974KA11).
Astrophysical question: (1973BA1H, 1973IB1A, 1973SM1A, 1973TR1C, 1973WE1D, 1974KO1C, 1974PA10, 1974RA09, 1974SH1D, 1975HO1C, 1975KI14, 1975SC1H, 1976BE1C, 1976BO1E, 1976CL1A, 1976CO1B, 1976FU1B, 1976GI1C, 1976HE15, 1976PE1A, 1976RA1C, 1976SI1C, 1976VI1A, 1977AU1B, 1977BA1V, 1977BI1E, 1977GA1C, 1977HA1L, 1977KO1J, 1977MO1E, 1977SC1D, 1977SI1D, 1978ME1D).
Applied work: (1976WI1B).
Special reactions: (1974BA70, 1974BO08, 1974DI16, 1974HA11, 1974KA22, 1974PA10, 1974PE1C, 1974RA09, 1974RA11, 1975FU01, 1975HO12, 1975HU10, 1975RA12, 1975RA14, 1975RA21, 1975RA25, 1975RE18, 1975RU09, 1975WI1D, 1975ZE01, 1975ZE03, 1976BE1K, 1976BO08, 1976BU16, 1976CU05, 1976DI01, 1976HE15, 1976HU1D, 1976IN04, 1976LE1F, 1976MA1D, 1976MI13, 1976OS04, 1976RA1C, 1976SI1D, 1976ST11, 1977AR06, 1977AS03, 1977BI1E, 1977GO07, 1977ST34, 1977ST1G, 1977YA1B, 1978BI08, 1978CU01, 1978DI04, 1978GE1C, 1978GR1F, 1978WE1D).
Ground state properties of 7Be: (1975BE31).
The decay is complex: see 7Li.
In the range Eα = 0.38 to 5.80 MeV the cross section rises from 8 × 10-3 to 4 μb (1963PA12, 1969NA24). The capture proceeds mainly by E1, with both s- and d-waves contributing above Eα = 1 MeV (1963TO06). The branching ratio γ1/γ0 [7Be*(0.43)/7Be(0)] is approximately constant at 37% for Eα = 0.57 to 3.2 MeV (1963PA12, 1969NA24). The zero-energy intercept of the cross-section factor S = 0.61 ± 0.07 keV · b and (dS/dE)0 = -(5.8 ± 0.3) × 10-4 b using all the data. If the low-energy data (Ec.m. ≤ 0.7 MeV) is fitted using a direct capture calculation (1963TO06) the zero-energy intercept of the cross-section factor is S = 0.51 ± 0.05 keV · b and (dS/dE)0 = -(2.8 ± 0.4) × 10-4 b (1969NA24). A second-order (in energy) polynomial fit to the low-energy data (Ec.m. ≤ 0.8 MeV) determines S = 0.61 ± 0.07 keV · b and (dS/dE)0 = -(5.8 ± 0.3) × 10-4 b (1969NA24). Recent papers discussing the astrophysical implications of this reaction are (1971BA1A, 1974VA1C, 1976NO1C).
Elastic scattering studies have been reported for E(3He) = 1.72 to 140 MeV [see (1974AJ01)] and at Eα = 22.8 to 26.4 MeV (1976ZA11) and 65.3 to 102.7 MeV (1973FE1B). The total reaction cross section at E(3He) = 28 MeV is 433 ± 10 mb (1977KO09). Polarization measurements have been carried out at E(3He) = 7.8 to 13 MeV and Eα = 4.3 to 18.5 MeV [see (1974AJ01)], E(3He) = 18 → 32 MeV (1978LU05), and at Eα = 24.5 to 42 MeV (1976BA1L; on 3He-bar), E(3He-bar) = 38.2 MeV (1976BI1C) and at Eα = 98 MeV (1973FE1B). For an R-matrix analysis of the 2F5/2 state at Ex = 6.73 MeV, see (1976DO1B).
For l ≤ 4, only f-wave phase shifts show resonance structure for E(3He) < 18 MeV, corresponding to 7Be*(4.57, 6.73, 9.27): see Table 7.7 (in PDF or PS) (1967SP10). No structure corresponding to 7Be*(7.21) (Jπ = 5/2-) is seen in the elastic data. The s-wave phase shift is somewhat greater than hard-sphere; the p-wave splitting agrees with (1964BA09, 1967SP10). The decay of 7Be*(9.27) (Jπ = 7/2-) to 6Li(0) requires f-shell configuration admixture. An estimate of the yield of ground state protons relative to those corresponding to 6Li*(2.19) yields γ2(p0)/γ2(p1) = (16+5-10)% (1967SP10). A phase shift analysis (single-level R-matrix) has been carried out for E(3He) = 18 to 32 MeV: the p-wave phase shifts indicate a 1/2- state at Ex ≈ 16.7 MeV (Er = 26.4 MeV), with Γ = 6.5 MeV (1978LU05). At higher energies [E(3He) = 27.2 to 42.8 MeV] (1969SC16) report that the s- and f-wave phase shifts fall appreciably below the predictions of resonating group calculations, while (1970BR42) see some indication of broad resonant structure at E(3He) ≈ 34 MeV, in rough qualitative agreement with such calculations. The bremsstrahlung cross section at E(3He) = 7.4 MeV is 12.6 ± 3.4 μb/sr2 (1973FR17).
The differential reaction cross section for reaction (b) has been determined for E(3He) = 8 to 18 MeV (1967SP10) and at 28 MeV (1977KO09: d0, d1, d2): resonances are observed corresponding to 7Be*(7.21, 9.27) in the p0 yield and to 7Be*(9.27) in the p1 yield: see Table 7.7 (in PDF or PS) (1967SP10). A study of the γ-rays from 6Li*(3.56) (p2) carried out at E(3He) = 13.8 to 18.5 MeV shows the excitation of two Jπ = 3/2- states at Ex ≈ 10.0 MeV (T = 1/2) and 11.00 ± 0.05 MeV (Γ = 400 ± 50 keV, θ2p2 = 0.13 ± 0.02, T = 3/2). The T = 3/2 resonance is evidenced mainly through interference. There is also some evidence for an extremely broad Jπ = 1/2- structure at Ex ≳ 10 MeV (1967HA07, 1967HA08: see also 6Li(p, p)6Li). At E(3He) = 28 MeV sequential breakup via 6Li*(2.19) significantly contributes to the reaction mechanism (1977KO09).
The production cross section for 7Be has been measured for Eα = 39.4 to 47.4 MeV: it is essentially equal to that for the (α, p) reaction above 43 MeV but is smaller below because of threshold effects. See also (1977RA1B; prelim., Eα = 400, 600 and 1000 MeV). For a discussion of the production of 7Li in the galaxy, see (1975KI14, 1977KI12) and reaction 4 in 7Li. See also (1974KO1C; astrophys.) and 8Be.
Gamma transitions are observed to the ground (γ0) and to the 0.43 MeV (γ1) states. The yield shows no evidence of resonance for Ep = 0.2 to 1.0 MeV and the branching ratio remains approximately constant at (62 ± 5)% to the ground state, 38% to 7Be*(0.43), < 4% to 7Be*(4.57): see (1974AJ01).
Measurements of elastic angular distributions have been reported for Ep = 0.5 to 600 MeV: see (1966LA04, 1974AJ01) and 6Li. Two resonances are reported at Ep = 1.84 and 5 MeV in the elastic yield [7Be*(7.21, 9.9)]. The parameters of the lower resonance are shown in Table 7.4 (in PDF or PS) (1963MC09). The 5 MeV resonance has Γ ≈ 1.8 MeV and appears to also be formed by p-waves: γ2p is then 3 ± 2 MeV · fm. A weak rise near Ep = 8 to 9 MeV may indicate a further level, 7Be* ≈ 13 MeV (1963HA53). A broad resonance at Ep = 14 MeV is suggested by (1977NE1A). Polarization measurements have been carried out for Ep = 1.2 to 155 MeV [see (1974AJ01)], at Ep-bar = 32 MeV (1976MO1B: p1, p2). A phase shift analysis for Ep = 0.5 to 5.6 MeV shows that only 2S, 4S and 4P are involved. The 4P5/2 phase resonates at Ep = 1.8 MeV, and the broad resonance at 5 MeV can be reproduced equally well by either 4P3/2 or 4P1/2: tensor polarization measurements are necessary to distinguish between the two (1969PE22). An R-matrix analysis of the 2F5/2 state at Ex = 6.73 MeV is reported by (1976DO1B).
The reaction cross section for formation of 6Li*(2.19) has been measured for Ep = 3.6 to 9.40 MeV: a broad resonance indicates the presence of a state with Ex ≈ 10 MeV, Γ = 1.8 MeV, Jπ = (3/2, 5/2)-, T = 1/2 (1967HA07, 1967HA08). The cross-section and angular distributions of p2 (6Li*(3.56)) for Ep = 4.26 to 9.40 MeV is analyzed in terms of two Jπ = 3/2- states at Ex ≈ 10 and 11 MeV: see reaction 3 (1967HA07, 1967HA08). The total cross section for formation of 6Li*(3.56) decreases slowly with energy for Ep = 24.3 to 46.4 MeV (1968AU06). The reaction cross section has been measured for Ep = 25.0 to 48 MeV by (1976SO1B).
For reaction (b) see 5He and (1977NA16). For reaction (c) see 6Li and the polarization measurements of (1974DU10) and (1976DU1C) at Ep = 40 and 19.4 MeV, respectively. See also (1977FR1F, 1978FR1D), (1977MC1C; applied) and (1975BA05, 1977BI1E, 1978MA37; theor.).
Over the range Ep = 25 to 50 keV, the cross section rises from 0.8 to 72 μb: in the formula σ ≈ E-1e-B/√E(square root of E), B = 90 ± 6 keV1/2 (1967FI05). Cross-section measurements for Ep = 62 to 188 keV show deviation from an s-wave Gamow plot above ≈ 130 keV (1966GE11). Using cross-section measurements at Ep = 151 and 317 keV, as well as the (1966GE11) data (1971SP05) calculate S(0) = 3.0 MeV · b. See also (1978EL1A: Ep = 0.1 to 1.0 MeV).
At higher energies the cross section exhibits a broad, low maximum near Ep = 1 MeV and a pronounced resonance at Ep = 1.85 MeV (1951BA79, 1956MA91) and (1977LI01: Γ < 0.5 MeV; Ep = 1.0 to 2.6 MeV). No other structure is reported up to Ep = 5.6 MeV: see (1974AJ01). Measurements between Ep = 0.4 and 3.4 MeV show that the polarizations are generally large and positive. The Ep = 1.9 MeV resonance appears in A1 and A2 (1968BR18).
Angular distributions have been reported for Ep = 0.15 to 16 MeV [see (1974AJ01)] and at Ep = 0.5 to 1.82 MeV (1974JO08), 1.0 to 2.0 MeV (1977LI01), 25.5 to 45 MeV (1974SC24) and 45 MeV (1971BR12). Angular distributions at Ep = 8 to 18.5 MeV have been analyzed using a finite-range multi-interaction DWBA formalism. The analysis leads to reduced widths of 0.69 for α + d in a relative s-state, 0.04 for α + d in a relative d-state and 0.44 for 3He + t in a relative s-state (1973WE07). A polarization measurement is reported at E(6Li) = 16.8 MeV (1976FI1B).
The n-γ correlations are isotropic, indicating Jπ = 1/2- for 7Be*(0.43) (1956NE13). Broad maxima are observed in the ratio of low-energy to high-energy neutrons at Ed = 4.2 and 5.1 MeV [7Be*(6.5, 7.2), Γc.m. = 1.2 and 0.5 MeV, respectively] (1957SL01). See also (1974MCZS, 1975MC02, 1977GL05) in 8Be.
Angular distributions of the d0 and d1 groups to 7Be*(0, 0.43) have been measured at Ed = 8, 10, 14 and 18 MeV: all the distributions show an l = 1 maximum at small angles. The DWBA analysis leads to a ratio of spectroscopic factors S*/S [for 7Be*(0.43)/7Be(0)] = 1.55, in fair agreement with other measurements (1968LU02).
Angular distributions of t0, t1 and t2 have been reported at Eα = 40 to 46 MeV: see (1974AJ01). [Some of the reported work is unpublished.]
Ethresh. = 1880.59 ± 0.08 keV [recommended by (1970RO07)]. The excitation energy of 7Be*(0.43) is 429.20 ± 0.10 keV (1972BO02); τm = 192 ± 25 fsec (1966PA11). [(1976DO10) report 136 ± 10 fsec.] Angular distributions are reported at Ep = 1.9 to 50 MeV [see (1974AJ01)] and at 2.1 to 3.8 MeV (1974BU16: n0), 3.1 to 4.9 MeV (1976BR1E: n1), 14.9 and 17.8 MeV (1974AR05: n0, n1 (not resolved at the lower energy)), 15.1 to 26 MeV (1976PO06: n0, n1), and 24.8, 35.0 and 45.0 MeV (1977SC37: n0, n1). (1976PO06) also report the population of 7Be*(4.55, 6.51, 7.19, 10.79). See also (1977RI07: Ep = 800 MeV) and (1974AJ01).
Angular distributions of tritons have been measured at Ep = 43.7 MeV (1965DE08, 1966CE05, 1968BR23: 7Be*(0, 0.43, 4.57, 6.51, 11.01)) and 46 MeV (1967VE01: 7Be*(0 + 0.43, 4.57, 6.51, 10.69)). The 11 MeV state has Ex = 11.01 ± 0.04 MeV (1968BR23), Γ = 298 ± 25 keV, Jπ = 3/2-, T = 3/2 [the Jπ; T assignments are based on the similarity of the angular distribution to that in the (p, 3He) reaction to 7Li*(11.13)] (1965DE08). The ratio of the cross section for formation of 7Be*(0.43) to that for formation of 7Li*(0.48) [in the (p, 3He) mirror reaction] has been measured for Ep = 14.8 to 27 MeV (1975HA1K).
At Eα = 45.6 MeV (1969FO06) have measured the angular distributions of the 7Li and of the 7Be ions, corresponding to the ground state transitions. At a given angle the intensities of the two ions are the same, implying that the wave functions of the ground states of 7Li and 7Be are very similar (1969FO06).
At Ed = 39.8 MeV angular distributions have been measured for the transitions 7Li(0) + 7Be(0), 7Li*(0.48) + 7Be(0), 7Li(0) + 7Be*(0.43) and 7Li*(0.48) + 7Be*(0.43). The ratios of the 7Li(0) and 7Be(0) cross sections show asymmetries exceeding 20% (1971YO06). See also (1974VA1A).
Angular distributions have been obtained at E(3He) = 25.5 to 29 MeV (1976PI10: 7Be*(0, 0.43)) and 28 and 30 MeV (1970DE12: 7Be*(0, 0.43)+8Be*(0, 2.9)). See also (1974AJ01), (1976PA07, 1973OG1A), (1974DO03; theor.) and 15O in (1976AJ04).
At Eα = 42 MeV, angular distributions have been measured to 7Be*(0, 0.43) + 9Be(0) (1972RU03).
At Ep = 45.0 MeV the angular distribution has been measured for the transition to 7Li(0) + 7Be(0) (1971BR07).
See 13C in (1976AJ04).
At Eα = 42 MeV, angular distributions have been obtained for the transitions to 7Be*(0, 0.43) + 13C(0) (1972RU03).
The angular distributions to 7Be*(0 + 0.43) + 14C(0) has been measured at Ed = 14.9 MeV (1967DE03).
(1970DE12) have studied at E(3He) = 30 MeV the angular distributions to 15N(0) + 7Be*(0, 0.43) and to 16O*(0, 6.06 + 6.13) + 7Be*(0, 0.43).