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USNDP

7Be (1974AJ01)


(See Energy Level Diagrams for 7Be)

GENERAL: See also (1966LA04) and Table 7.5 [Table of Energy Levels] (in PDF or PS).

Shell model: (1961KO1A, 1965VO1A, 1966BA26, 1966HA18, 1967FA1A, 1968GO01, 1969TA1H, 1971CO28, 1971NO02, 1972LE1L, 1973HA49).

Cluster model: (1965NE1B, 1968HA1G, 1971NO02, 1972HI16, 1972KU12, 1972LE1L).

Rotational and deformed models: (1965VO1A, 1966EL08).

Special levels: (1966BA26, 1966EL08, 1967FA1A, 1969HA1G, 1969HA1F, 1971CO28, 1971NO02, 1972BB26, 1973AS02, 1973FE1J).

Electromagnetic transitions: (1966BA26, 1966EL08, 1969HA1G, 1969HA1F, 1973AS02, 1973HA49).

Astrophysical questions: (1968BA2F, 1968HA1C, 1970BA1M, 1972KO1E, 1972PA1C, 1972UL1A, 1973LA19, 1973RA37, 1973SC1T).

Special reactions: (1965FU1A, 1966GA15, 1966MI1C, 1967AU1B, 1967FU1E, 1967WI06, 1967WI20, 1968BE1F, 1968DI1B, 1968HU1D, 1968MI1D, 1968RA34, 1968SH1H, 1968YI01, 1969DI18, 1969HI1A, 1969YI1A, 1970BR13, 1970MA1E, 1971AR02, 1971BA58, 1971BI22, 1971BR36, 1971DM01, 1971EP02, 1971HE24, 1971MO1H, 1971NO09, 1971ST30, 1972AM04, 1973ER1G, 1973HO11, 1973JO07, 1973LA19, 1973MI02, 1973VO1G).

Reactions involving pions: (1968BE1F).

Other topics: (1965BO1C, 1965VO1A, 1966DE1E, 1966HA18, 1966YO1B, 1967CA17, 1967FA1A, 1968BE1F, 1968GO01, 1969HE1N, 1969VI1C, 1970DE1P, 1971ZA1D, 1972AB14, 1972AN05, 1972BB26, 1972CA37, 1972LE1L, 1972PN1A, 1973JU2A, 1973RO1R).

Ground-state properties: (1965VO1A, 1966BA26, 1966EL08, 1969PE1D, 1972LE1L, 1973MA1K).

1. 7Be(ε)7Li Qm = 0.8618

The decay is complex: see 7Li.

2. 4He(3He, γ)7Be Qm = 1.5864

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 γ10 [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 of the data. If the low-energy data (Ecm ≤ 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) polynominal fit to the low-energy data (Ecm ≤ 0.8 MeV) determines S = 0.61 ± 0.07 keV · b and (dS/dE)0 = -(5.8 ± 0.3) b (1969NA24). Recent papers discussing the astrophysical implications of this reaction are (1967TO1B, 1968BA2E, 1971CA1B, 1972KA1B, 1973BA2C, 1973TR1E). See also (1966LA04).

3. (a) 4He(3He, 3He)4He Eb = 1.5864
(b) 4He(3He, p)6Li Qm = -4.0200

Elastic scattering studies have previously been reported for E(3He) = 2.5 to 30 MeV and for Eα = 11 to 41 MeV: See (1966LA04). More recent measurements have been made at E(3He) = 1.72, 2.46, 2.98 MeV (1971CH42), 5 to 18 MeV (1967SP10), 12.0 to 19.0 MeV (1967DU1B), 17.8 to 30.0 MeV (1970JA04), 18 to 70 MeV (1969BA2B), 19.5 to 51.1 MeV (1970BR42), 27.2 to 42.8 MeV (1969SC16) and at Eα = 5.94 to 7.90 MeV (1968IV01), 42 MeV (1970VI01), 43.4 to 58.2 MeV (1969CA1E), 66 to 104 MeV (1971FE02, 1971FE03, 1973FE11) and 140 MeV (1972FR1J, 1972PU1C, 1972FR1K). Differential cross sections have been calculated by (1973KO1Q) for Ecm < 44.5 MeV using the one-channel resonating = group method, and including exchange terms and odd-even absorption. Polarization measurements have been carried out at E(3He) = 7.8 to 13.0 MeV (1969AR07, 1971AR1K) and at 11.5 to 13.0 MeV (1970MC07), and at Eα = 4.33 to 9.83 MeV (1972BO42), 7.5 to 18.5 MeV (1970HA1M, 1970HA1P, 1972HA64), 13.0 MeV (1971AR1K) and 98 MeV (1973FE11). The ratios of γ2 to the Wigner limit are, respectively, 0.31-0.09+0.04 and 0.29-0.16+0.07 for 7Be*(0, 0.43) (1972BO42).

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 7.6 (in PDF or PS) (1967SP10, 1968IV01). 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). 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. For inelastic scattering in reaction (a) see (1971HA21) and (1973FI04). 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: 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 7.6 (in PDF or PS) (1967SP10). A study of the gamma 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 evidence for an extremely broad Jπ = 1/2- structure at Ex ≳ 10 MeV (1967HA07, 1967HA08: see also 6Li(p, p)6Li).

See also (1970LI06, 1972BI1G, 1973KO1R), (1966PH1A) and (1966BA26, 1966RA1B, 1966TH1C, 1967OK1A, 1968BR1H, 1968LE1K, 1969TA1G, 1970NE1F, 1971FU09, 1971KU22, 1971PL06, 1971TA23, 1972BR1Q, 1972CL1C, 1972NE17; theor.).

4. 4He(α, n)7Be Qm = -18.9921

See 8Be.

5. 6Li(p, γ)7Be Qm = 5.6064

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) (1955BA59, 1956WA03, 1969JO1K, 1969SW1C). At Ep = 1.06 MeV a resonance in the yield of 0.43 MeV γ-rays is reported by (1968WO1E), corresponding to7Be*(6.52). See, however, (1963MC09). See also (1966LA1D) and (1966LA04).

6. (a) 6Li(p, p)6Li Eb = 5.6064
(b) 6Li(p, 2p)5He Qm = -4.59

Measurements of elastic angular distributions have recently been reported by (1968ME25: Ep = 14 to 15.8 MeV). Earlier measurements are listed in (1966LA04). 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 7.3 (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). Differential cross sections are reported by (1971BI11: 6.868 MeV) and by (1969LE08: 1.36 MeV). See also 6Li. Polarization measurements (elastic scattering) have been carried out at Ep = 1.21 to 3.22 MeV (1969PE22), 14.5 MeV (1965RO22), 49.8 MeV (1971MA13), 152 MeV (1966RO1C), and 155 MeV (1968GE04). A phase-shify analysis for Ep = 0.5 to 5.6 MeV shows that only 2S, 4S and 4P are involved. The 4P5/2 phase resonantes 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). See (1966LA04) for earlier results. An S-matrix analysis of the cross section of this reaction and of reactions 3 and 9 has been reported by (1966HU1C, 1968LE1K).

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 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). Polarization measurements involving the p1 and p2 groups have been carried out Ep = 49.8 MeV (1971MA44). For the total scattering cross section at 1 GeV, see (1967IG1A).

See also (1967CA1G, 1968OL1B), (1971PL1C), (1966LE1E, 1969WA11, 1970LE02, 1972BR20, 1973LA26; theor.). For reaction (b) see 6Li, 5He and (1973NA1M).

7. 6Li(p, n)6Be Qm = -5.070 Eb = 5.6064

The yield of neutrons increases approximately monotonically from threshold to Ep = 14.3 MeV (1964BA16). See also (1971BU1D). For polarization measurements at Ep = 30 and 50 MeV, see (1969RO20). See also (1969CL06, 1971JU05), (1970RA33; theor.) and 6Be.

8. 6Li(p, d)5Li Qm = -3.44 Eb = 5.6064

See 5Li.

9. 6Li(p, α)3He Qm = 4.0200 Eb = 5.6064

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 (1969AU1C).

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). No other structure is reported up to Ep = 5.6 MeV (1963JE03, 1964FA03). 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). S-matrix analysis of the cross section of this reaction and of reactions 3 and 6 are reported by (1966HU1C, 1968LE1K). Angular distributions are reported at Ep = 151 and 317 keV (1971SP05), at Ep = 0.5 to 1.82 MeV (1969JO1J), 3 to 45 MeV (1973SC1V) and 12, 14 and 16 MeV (1973WE07). 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). Yield and cross section measurements are reported by (1968BE1P: 0.3 to 1.0 MeV) and (1969LE08: Ep = 1.36 MeV). See also (1974GO1V) and see (1966LA04) for earlier measurements.

Searches for excited states of 3He have been unsuccessful: see (1968OL1B: Ep = 20 MeV), (1971BR12, 1972BU16: Ep = 45 MeV). See also (1970KO25, 1972BE1Y). See (1971BR12, 1973FI04) for discussions of the excited states of 4He.

See also (1967SP09, 1967VA1F) and (1969BE1M, 1969BO1G, 1972CL1C, 1972HU09: theor.).

10. 6Li(d, n)7Be Qm = 3.3818

Two neutron groups are observed, corresponding to 7Be*(0, 0.43). Angular distributions of the n0 and n1 groups have been measured at Ed = 0.24 to 3.5 MeV [see (1966LA04) and (1966SC26)]: lp = 1, Jπ ≤ 5/2- for both states. At Ed = 12, 15 and 17 MeV differential cross sections for the population of 7Be(g.s. + 0.43) have been measured by (1970GA07).

The n-γ correlations are isotropic, indicating Jπ = 1/2- for 7Be*(0.43) (1956NE13): Eγ = 428.9 ± 2 keV (1952TH24). 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), Γcm = 1.2 and 0.5 MeV, respectively] (1957SL01).

11. 6Li(3He, d)7Be Qm = 0.1126

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). See also (1964MA57) and (1970JA1J: theor.).

12. 6Li(α, t)7Be Qm = -14.2082

Angular distributions of triton groups have been reported at Eα = 40 MeV (1965OG03: 7Be*(0 + 0.43, 4.57 + (5.0 ± 0.3)), 43 MeV (1967DE1K: 7Be*(0, 0.43)) and 46 MeV (1969FO1C: 7Be*(0, 0.43, 4.57)). See also (1967OG1A).

13. 7Li(p, n)7Be Qm = -1.64422

Ethresh. = 1880.612 ± 0.090 keV (1970RO07); the recommended value for Ethresh. based on this and on other experiments is 1880.59 ± 0.08 keV (1970RO07). See also (1966MA60, 1966RO09, 1967MA1D, 1973MA1V). The excitation energy of the first excited state is 429.20 ± 0.10 keV (1972BO02). The lifetime of 7Be*(0.43), τm = 1.92 ± 0.2 msec. The ratio of this lifetime to that of 7Li*(0.48) is 1.82 ± 0.20. This value, and the values of τm are in agreement with intermediate coupling calculations assuming LS coupling predominates (a/K < 3.6) (1966PA11).

Angular distributions are reported at Ep = 1.9 to 2.36 MeV (1967BE61; n0), 2.1 to 3.8 MeV (1971BU1D; n0), 2.6 to 5.4 MeV (1972EL19; n0), 3.2 to 5.4 MeV (1972EL19; n1), at 17.5 MeV (1972AZ01; n0, n1, n2) and at 30 and 50 MeV (1969CL06; n0 + n1). Above Ep ≈ 7 MeV, neutrons corresponding to 7Be*(4.57) are seen (1959AJ81, 1960HI04, 1963BO06). At Ep = 30 to 50 MeV, neutron groups are observed to states at Ex = 4.61 ± 0.07, 7.21 ± 0.06, 9.6 ± 0.3, 11.3 ± 0.2, 12.3 ± 0.2, 13.24 ± 0.15, 14.39 ± 0.15, 15.3 ± 0.2, 16.3 ± 0.2, 18.3 ± 0.2, 19.7 ± 0.3 ande 20.5 ± 0.2 MeV (1965BA39). See also (1967LO07, 1969JU1A, 1970BO1U, 1971DA24, 1971WA1J), (1966PA04, 1969MA1P, 1969MA1G, 1968TH1H, 1971TH1K; theor.), (1966LA04) and 8Be.

14. 7Li(3He, t)7Be Qm = -0.8804

Angular distributions have been measured at E(3He) = 3.0 to 4.0 MeV (1969OR01; t0, t1), 8.7 and 9.7 MeV (1968MA1W; t0, t1), 14 MeV (1969NU1A; t0, t1) and 25.2 MeV (1968BR1G; t0, t1, t2). The width of 7Be*(4.57), Γcm = 175 ± 7 keV (1971PI06). See also (1967BL1E) and (1971WE1L, 1971WE1M; theor.).

15. 7Li(6Li, 6He)7Be Qm = -4.372

At E(6Li) = 31.8 MeV, the reaction is observed to 7Be*((0 + 0.43), 4.57) (1971CH1B).

16. 9Be(p, t)7Be Qm = -12.0831

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, 10.79)). 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). See also (1967MC14), (1969BA1Z, 1969IN1A) and (1967BA1E; theor.).

17. 10B(p, α)7Be Qm = 1.1462

Alpha groups corresponding to 7Be*(0, 0.43) have been studied by many observers: see (1952AJ38, 1959AJ76). Some reported values for the energy of the first excited state are: 431 ± 5 keV (1950VA01), 434.4 ± 4 keV (1951BR10), 429 ± 3 keV (1952CR30), 428.5 ± 1.8 keV (1952TH24). In addition the excitation of 7Li*(4.72 ± 0.08, 6.27 ± 0.10, 7.21 ± 0.10, (14.6 ± 0.3)) is reported by (1955RE16). At Ep = 18.6 MeV (θ = 30°) (1968PA15) find that the intensity of a group to 7Be*(14.6) is < 2% that reported by (1955RE16). Angular distributions have been measured at Ep = 2.8 to 7.0 MeV (1964JE01). See also 11C in (1975AJ02) and (1966LA04).

18. 10B(3He, 6Li)7Be Qm = -2.874

At E(3He) = 30.0 MeV angular distributions have been obtained for the transitions to 7Be*(0, 0.43) + 6Li*(0, 2.19): see (1970DE12, 1972OH01).

19. 10B(α, 7Li)7Be Qm = -16.202

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). See also (1971RO1A, 1971SI28, 1973NA1N; theor.).

20. 11B(d, 6He)7Be Qm = -11.563

At Ed = 40 MeV the cross section of the ground-state reaction is twice (to ± 10%) that for the reaction to 6Li*(3.56) + 7Li(0), in agreement with isospin conservation (1972GO1P).

21. 11B(3He, 7Li)7Be Qm = -7.079

See (1971RO1A).

22. 12C(p, 6Li)7Be Qm = -22.569

At Ep = 36.0, 40.7, 45.0, 50.0 and 56.8 MeV angular distributions have been obtained for the transitions to 7Be*(0 + 0.43) (1971BR07, 1971HO25, 1971HO1K).

23. 12C(d, 7Li)7Be Qm = -17.543

At Ed = 39.8 MeV angular distributions have been measured for the transitions 7Li(0) + 7Be(0), 7Li*(0.43) + 7Be(0), 7Li(0) + 7Be*(0.43) and 7Li*(0.43) + 7Be*(0.43). The ratios of the 7Li(0) and 7Be(0) cross sections show asymmetries exceeding 20% (1971HO1K, 1971YO06). See also (1971SI28; theor.).

24. 12C(3He, 8Be)7Be Qm = -5.780

Angular distributions have been obtained at E(3He) = 25.5 to 29 MeV (1972PI1A, 1973PI1D: 7Be*(0, 0.43)), 28 and 30 MeV (1970DE12, 1973KL1B: 7Be*(0, 0.43) + 8Be*(0, 2.9)), 35.6 MeV (1969NE1D, 1969ZE1A, 1970FO1D: 7Be*(0, 0.43)) and 37 and 41 MeV (1967ZA1B: 7Be*(0 + 0.43)). See also (1965EN01).

25. 12C(α, 9Be)7Be Qm = -24.694

At Eα = 42 MeV, angular distributions have been measured to 7Be*(0, 0.43) + 9Be(0) (1972RU03).

26. 13C(p, 7Li)7Be Qm = -20.264

At Ep = 45.0 MeV the angular distribution has been measured for the transition to 7Li(0) + 7Be(0) (1971BR07).

27. 16O(p, 10B)7Be Qm = -25.270

See (1969HO1H).

28. 16O(3He, 12C)7Be Qm = -5.575

Angular distributions are reported at E(3He) = 25.5 to 29 MeV (1972PI1A: to 7Be*(0, 0.43)), 30 MeV (1970DE12, 1973KL1B: to 12C*(0, 4.4, 7.7, 9.6) + 7Be*(0, 0.43)) and 41 MeV (1967ZA1B).

29. 16O(α, 13C)7Be Qm = -21.207

At Eα = 42 MeV, angular distributions have been obtained for the transitions to 7Be*(0, 0.43) + 13C(0) (1972RU03).

30. 19F(d, 14C)7Be Qm = -7.140

The angular distribution to 7Be*(0 + 0.43) + 14C(0) has been measured at Ed = 14.9 MeV (1967DE03).

31. (a) 19F(3He, 15N)7Be Qm = -2.426
(b) 20Ne(3He, 16O)7Be Qm = -3.144

(1970DE12, 1973KL1B) 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).