
^{7}Be (1974AJ01)(See Energy Level Diagrams for ^{7}Be) 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: (1965FU19, 1966GA15, 1966MI1C, 1967AU1B, 1967FU1E, 1967WI06, 1967WI20, 1968BE1F, 1968DI1B, 1968HU18, 1968MI1D, 1968RA34, 1968SH26, 1968YI01, 1969DI18, 1969HI1A, 1969YI1A, 1970BR13, 1970MA1E, 1970MO38, 1971AR02, 1971BA58, 1971BI22, 1971BR36, 1971DM01, 1971EP02, 1971HE24, 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). Groundstate properties: (1965VO1A, 1966BA26, 1966EL08, 1968PE16, 1972LE1L, 1973MA1K).
The decay is complex: see ^{7}Li.
In the range E_{α} = 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 dwaves contributing above E_{α} = 1 MeV (1963TO06). The branching ratio γ_{1}/γ_{0} [^{7}Be*(0.43)/^{7}Be(0)] is approximately constant at 37% for E_{α} = 0.57 to 3.2 MeV (1963PA12, 1969NA24). The zeroenergy intercept of the crosssection 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 lowenergy data (E_{cm} ≤ 0.7 MeV) is fitted using a direct capture calculation (1963TO06) the zeroenergy intercept of the crosssection factor is S = 0.51 ± 0.05 keV · b and (dS/dE)_{0} = (2.8 ± 0.4) × 10^{4} b (1969NA24). A secondorder (in energy) polynominal fit to the lowenergy data (E_{cm} ≤ 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).
Elastic scattering studies have previously been reported for E(^{3}He) = 2.5 to 30 MeV and for E_{α} = 11 to 41 MeV: See (1966LA04). More recent measurements have been made at E(^{3}He) = 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 E_{α} = 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 E_{cm} < 44.5 MeV using the onechannel resonating = group method, and including exchange terms and oddeven absorption. Polarization measurements have been carried out at E(^{3}He) = 7.8 to 13.0 MeV (1969AR07, 1971AR1K) and at 11.5 to 13.0 MeV (1970MC07), and at E_{α} = 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 γ^{2} to the Wigner limit are, respectively, 0.31^{0.09}_{+0.04} and 0.29^{0.16}_{+0.07} for ^{7}Be*(0, 0.43) (1972BO42). For l ≤ 4, only fwave phase shifts show resonance structure for E(^{3}He) < 18 MeV, corresponding to ^{7}Be*(4.57, 6.73, 9.27): see Table 7.6 (in PDF or PS) (1967SP10, 1968IV01). No structure corresponding to ^{7}Be*(7.21) (J^{π} = 5/2^{}) is seen in the elastic data. The swave phase shift is somewhat greater than hardsphere; the pwave splitting agrees with (1964BA09, 1967SP10). The decay of ^{7}Be*(9.27) (J^{π} = 7/2^{}) to ^{6}Li(0) requires fshell configuration admixture. An estimate of the yield of ground state protons relative to those corresponding to ^{6}Li*(2.19) yields γ^{2}(p_{0})/γ^{2}(p_{1}) = 16^{+5}_{10}% (1967SP10). At higher energies [E(^{3}He) = 27.2 to 42.8 MeV] (1969SC16) report that the s and fwave phase shifts fall appreciably below the predictions of resonating group calculations, while (1970BR42) see some indication of broad resonant structure at E(^{3}He) ≈ 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(^{3}He) = 7.4 MeV is 12.6 ± 3.4 μb/sr^{2} (1973FR17). The differential reaction cross section for reaction (b) has been determined for E(^{3}He) = 8 to 18 MeV: resonances are observed corresponding to ^{7}Be*(7.21, 9.27) in the p_{0} yield and to ^{7}Be*(9.27) in the p_{1} yield: see Table 7.6 (in PDF or PS) (1967SP10). A study of the gamma rays from ^{6}Li*(3.56) (p_{2}) carried out at E(^{3}He) = 13.8 to 18.5 MeV shows the excitation of two J^{π} = 3/2^{} states at E_{x} ≈ 10.0 MeV (T = 1/2) and 11.00 ± 0.05 MeV (Γ = 400 ± 50 keV, θ^{2}_{p2} = 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 J^{π} = 1/2^{} structure at E_{x} ≳ 10 MeV (1967HA07, 1967HA08: see also ^{6}Li(p, p)^{6}Li). See also (1970LI06, 1972BI1G, 1973KO1R), (1966PH1A) and (1966BA26, 1966RA1B, 1966TH1C, 1967OK1A, 1968BR1H, 1968LE1K, 1969TA1G, 1970NE1F, 1971FU09, 1971KU22, 1971PL06, 1971TA23, 1972BR1Q, 1972CL1C, 1972NE17; theor.).
See ^{8}Be.
Gamma transitions are observed to the ground (γ_{0}) and to the 0.43 MeV (γ_{1}) states. The yield shows no evidence of resonance for E_{p} = 0.2 to 1.0 MeV and the branching ratio remains approximately constant at (62 ± 5)% to the ground state, 38% to ^{7}Be*(0.43), < 4% to ^{7}Be*(4.57) (1955BA59, 1956WA03, 1969JO1K, 1969SW1C). At E_{p} = 1.06 MeV a resonance in the yield of 0.43 MeV γrays is reported by (1968WO1E), corresponding to^{7}Be*(6.52). See, however, (1963MC09). See also (1966LA1D) and (1966LA04).
Measurements of elastic angular distributions have recently been reported by (1968ME25: E_{p} = 14 to 15.8 MeV). Earlier measurements are listed in (1966LA04). Two resonances are reported at E_{p} = 1.84 and 5 MeV in the elastic yield [^{7}Be*(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 pwaves: γ^{2}_{p} is then 3 ± 2 MeV · fm. A weak rise near E_{p} = 8 to 9 MeV may indicate a further level, ^{7}Be* ≈ 13 MeV (1963HA53). Differential cross sections are reported by (1971BI11: 6.868 MeV) and by (1969LE08: 1.36 MeV). See also ^{6}Li. Polarization measurements (elastic scattering) have been carried out at E_{p} = 1.21 to 3.22 MeV (1969PE22), 14.5 MeV (1965RO22), 49.8 MeV (1971MA13), 152 MeV (1966RO1C), and 155 MeV (1968GE04). A phaseshify analysis for E_{p} = 0.5 to 5.6 MeV shows that only ^{2}S, ^{4}S and ^{4}P are involved. The ^{4}P_{5/2} phase resonantes at E_{p} = 1.8 MeV, and the broad resonance at 5 MeV can be reproduced equally well by either ^{4}P_{3/2} or ^{4}P_{1/2}: tensor polarization measurements are necessary to distinguish between the two (1969PE22). See (1966LA04) for earlier results. An Smatrix 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 ^{6}Li*(2.19) has been measured for E_{p} = 3.6 to 9.40 MeV: a broad resonance indicates the presence of a state with E_{x} ≈ 10 MeV, Γ = 1.8 MeV, J^{π} = (3/2, 5/2)^{}; T = 1/2 (1967HA07, 1967HA08). The cross section and terms of two J^{π} = 3/2^{} states at E_{x} ≈ 10 and 11 MeV: see reaction 3 (1967HA07, 1967HA08). The total cross section for formation of ^{6}Li*(3.56) decreases slowly with energy for E_{p} = 24.3 to 46.4 MeV (1968AU06). Polarization measurements involving the p_{1} and p_{2} groups have been carried out E_{p} = 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 ^{6}Li, ^{5}He and (1973NA1M).
The yield of neutrons increases approximately monotonically from threshold to E_{p} = 14.3 MeV (1964BA16). See also (1971BU1D). For polarization measurements at E_{p} = 30 and 50 MeV, see (1969RO20). See also (1969CL06, 1971JU05), (1970RA33; theor.) and ^{6}Be.
See ^{5}Li.
Over the range E_{p} = 25 to 50 keV, the cross section rises from 0.8 to 72 μb: in the formula σ ≈ E^{1}e^{B/√E (square root of E)}, B = 90 ± 6 keV^{1/2} (1967FI05). Cross section measurements for E_{p} = 62 to 188 keV show deviation from an swave Gamow plot above ≈ 130 keV (1966GE11). Using crosssection measurements at E_{p} = 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 E_{p} = 1 MeV and a pronounced resonance at E_{p} = 1.85 MeV (1951BA79, 1956MA91). No other structure is reported up to E_{p} = 5.6 MeV (1963JE03, 1964FA03). Measurements between E_{p} = 0.4 and 3.4 MeV show that the polarizations are generally large and positive. The E_{p} = 1.9 MeV resonance appears in A_{1} and A_{2} (1968BR18). Smatrix analysis of the cross section of this reaction and of reactions 3 and 6 are reported by (1966HU1C, 1968LE1K). Angular distributions are reported at E_{p} = 151 and 317 keV (1971SP05), at E_{p} = 0.5 to 1.82 MeV (1969JO1J), 3 to 45 MeV (1973SC1V) and 12, 14 and 16 MeV (1973WE07). Angular distributions at E_{p} = 8 to 18.5 MeV have been analyzed using a finiterange multiinteraction DWBA formalism. The analysis leads to reduced widths of 0.69 for α + d in a relative sstate, 0.04 for α + d in a relative dstate and 0.44 for ^{3}He + t in a relative sstate (1973WE07). Yield and cross section measurements are reported by (1968BE1P: 0.3 to 1.0 MeV) and (1969LE08: E_{p} = 1.36 MeV). See also (1974GO1V) and see (1966LA04) for earlier measurements. Searches for excited states of ^{3}He have been unsuccessful: see (1968OL1B: E_{p} = 20 MeV), (1971BR12, 1972BU16: E_{p} = 45 MeV). See also (1970KO25, 1972BE1Y). See (1971BR12, 1973FI04) for discussions of the excited states of ^{4}He. See also (1967SP09, 1967VA1F) and (1969BE1M, 1969BO1G, 1972CL1C, 1972HU09: theor.).
Two neutron groups are observed, corresponding to ^{7}Be*(0, 0.43). Angular distributions of the n_{0} and n_{1} groups have been measured at E_{d} = 0.24 to 3.5 MeV [see (1966LA04) and (1966SC26)]: l_{p} = 1, J^{π} ≤ 5/2^{} for both states. At E_{d} = 12, 15 and 17 MeV differential cross sections for the population of ^{7}Be(g.s. + 0.43) have been measured by (1970GA07). The nγ correlations are isotropic, indicating J^{π} = 1/2^{} for ^{7}Be*(0.43) (1956NE13): E_{γ} = 428.9 ± 2 keV (1952TH24). Broad maxima are observed in the ratio of lowenergy to highenergy neutrons at E_{d} = 4.2 and 5.1 MeV [^{7}Be*(6.5, 7.2), Γ_{cm} = 1.2 and 0.5 MeV, respectively] (1957SL01).
Angular distributions of the d_{0} and d_{1} groups to ^{7}Be*(0, 0.43) have been measured at E_{d} = 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 ^{7}Be*(0.43)/^{7}Be(0)] = 1.55, in fair agreement with other measurements (1968LU02). See also (1964MA57) and (1970JA1J: theor.).
Angular distributions of triton groups have been reported at E_{α} = 40 MeV (1965OG03: ^{7}Be*(0 + 0.43, 4.57 + (5.0 ± 0.3)), 43 MeV (1967DE1K: ^{7}Be*(0, 0.43)) and 46 MeV (1969FO1C: ^{7}Be*(0, 0.43, 4.57)). See also (1967OG1A).
E_{thresh.} = 1880.612 ± 0.090 keV (1970RO07); the recommended value for E_{thresh.} 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 ^{7}Be*(0.43), τ_{m} = 1.92 ± 0.2 msec. The ratio of this lifetime to that of ^{7}Li*(0.48) is 1.82 ± 0.20. This value, and the values of τ_{m} are in agreement with intermediate coupling calculations assuming LS coupling predominates (a/K < 3.6) (1966PA11). Angular distributions are reported at E_{p} = 1.9 to 2.36 MeV (1967BE61; n_{0}), 2.1 to 3.8 MeV (1971BU1D; n_{0}), 2.6 to 5.4 MeV (1972EL19; n_{0}), 3.2 to 5.4 MeV (1972EL19; n_{1}), at 17.5 MeV (1972AZ01; n_{0}, n_{1}, n_{2}) and at 30 and 50 MeV (1969CL06; n_{0} + n_{1}). Above E_{p} ≈ 7 MeV, neutrons corresponding to ^{7}Be*(4.57) are seen (1959AJ81, 1960HI04, 1963BO06). At E_{p} = 30 to 50 MeV, neutron groups are observed to states at E_{x} = 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 ^{8}Be.
Angular distributions have been measured at E(^{3}He) = 3.0 to 4.0 MeV (1969OR01; t_{0}, t_{1}), 8.7 and 9.7 MeV (1968MA1W; t_{0}, t_{1}), 14 MeV (1969NU1A; t_{0}, t_{1}) and 25.2 MeV (1968BR1G; t_{0}, t_{1}, t_{2}). The width of ^{7}Be*(4.57), Γ_{cm} = 175 ± 7 keV (1971PI06). See also (1967BL1E) and (1971WE1L, 1971WE1M; theor.).
At E(^{6}Li) = 31.8 MeV, the reaction is observed to ^{7}Be*((0 + 0.43), 4.57) (1971CH1B).
Angular distributions of tritons have been measured at E_{p} = 43.7 MeV (1965DE08, 1966CE05, 1968BR23: ^{7}Be*(0, 0.43, 4.57, 6.51, 11.01)) and 46 MeV (1967VE01: ^{7}Be(0 + 0.43, 4.57, 6.51, 10.79)). The 11 MeV state has E_{x} = 11.01 ± 0.04 MeV (1968BR23), Γ = 298 ± 25 keV, J^{π} = 3/2^{}; T = 3/2 [the J^{π}; T assignments are based on the similarity of the angular distribution to that in the (p, ^{3}He) reaction to ^{7}Li*(11.13)] (1965DE08). See also (1967MC14), (1969BA1Z, 1969IN1A) and (1967BA1E; theor.).
Alpha groups corresponding to ^{7}Be*(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 ^{7}Li*(4.72 ± 0.08, 6.27 ± 0.10, 7.21 ± 0.10, (14.6 ± 0.3)) is reported by (1955RE16). At E_{p} = 18.6 MeV (θ = 30°) (1968PA15) find that the intensity of a group to ^{7}Be*(14.6) is < 2% that reported by (1955RE16). Angular distributions have been measured at E_{p} = 2.8 to 7.0 MeV (1964JE01). See also ^{11}C in (1975AJ02) and (1966LA04).
At E(^{3}He) = 30.0 MeV angular distributions have been obtained for the transitions to ^{7}Be*(0, 0.43) + ^{6}Li*(0, 2.19): see (1970DE12, 1972OH01).
At E_{α} = 45.6 MeV (1969FO06) have measured the angular distributions of the ^{7}Li and of the ^{7}Be ions, corresponding to the groundstate transitions. At a given angle the intensities of the two ions are the same, implying that the wave functions of the ground states of ^{7}Li and ^{7}Be are very similar (1969FO06). See also (1971RO1A, 1971SI28, 1973NA1N; theor.).
At E_{d} = 40 MeV the cross section of the groundstate reaction is twice (to ± 10%) that for the reaction to ^{6}Li*(3.56) + ^{7}Li(0), in agreement with isospin conservation (1972GO1P).
See (1971RO1A).
At E_{p} = 36.0, 40.7, 45.0, 50.0 and 56.8 MeV angular distributions have been obtained for the transitions to ^{7}Be*(0 + 0.43) (1971BR07, 1971HO25, 1971HO1K).
At E_{d} = 39.8 MeV angular distributions have been measured for the transitions ^{7}Li(0) + ^{7}Be(0), ^{7}Li*(0.43) + ^{7}Be(0), ^{7}Li(0) + ^{7}Be*(0.43) and ^{7}Li*(0.43) + ^{7}Be*(0.43). The ratios of the ^{7}Li(0) and ^{7}Be(0) cross sections show asymmetries exceeding 20% (1971HO1K, 1971YO06). See also (1971SI28; theor.).
Angular distributions have been obtained at E(^{3}He) = 25.5 to 29 MeV (1972PI1A, 1973PI1D: ^{7}Be*(0, 0.43)), 28 and 30 MeV (1970DE12, 1973KL1B: ^{7}Be*(0, 0.43) + ^{8}Be*(0, 2.9)), 35.6 MeV (1969NE1D, 1969ZE1A, 1970FO1D: ^{7}Be*(0, 0.43)) and 37 and 41 MeV (1967ZA1B: ^{7}Be*(0 + 0.43)). See also (1965EN01).
At E_{α} = 42 MeV, angular distributions have been measured to ^{7}Be*(0, 0.43) + ^{9}Be(0) (1972RU03).
At E_{p} = 45.0 MeV the angular distribution has been measured for the transition to ^{7}Li(0) + ^{7}Be(0) (1971BR07).
See (1969HO1H).
Angular distributions are reported at E(^{3}He) = 25.5 to 29 MeV (1972PI1A: to ^{7}Be*(0, 0.43)), 30 MeV (1970DE12, 1973KL1B: to ^{12}C*(0, 4.4, 7.7, 9.6) + ^{7}Be*(0, 0.43)) and 41 MeV (1967ZA1B).
At E_{α} = 42 MeV, angular distributions have been obtained for the transitions to ^{7}Be*(0, 0.43) + ^{13}C(0) (1972RU03).
The angular distribution to ^{7}Be*(0 + 0.43) + ^{14}C(0) has been measured at E_{d} = 14.9 MeV (1967DE03).
(1970DE12, 1973KL1B) have studied, at E(^{3}He) = 30 MeV, the angular distributions to ^{15}N(0) + ^{7}Be*(0, 0.43) and to ^{16}O*(0, 6.06 + 6.13) + ^{7}Be*(0, 0.43).
