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USNDP

11Be (80AJ01)


(See Energy Level Diagrams for 11Be)

GENERAL: See also (75AJ02) and Table 11.1 [Table of Energy Levels] (in PDF or PS).

Model calculations:(TA74H, MI75M, IR76C, SE77B, BO78H, BE79A).

Special reactions:(FE75E, OS76B, AR77B, YA77D).

Muon capture (See also reaction 2.):(DE78C).

Pion reactions:(CO75E, CO76Q, DO77A, GE77H).

Ground state of 11Be:(BE75Q, BO78H).

1. 11Be(β-)11B Qm = 11.508

The decay proceeds to 11B*(0, 2.12, 5.02, 6.79, 7.98, 9.88) with Jπ = 3/2-, 1/2-, 3/2-, 1/2+, 3/2+, 3/2+, respectively: see Table 11.15 (in PDF or PS) (AL71B). The half-life is 13.81 ± 0.08 sec (AL70I). The nature of the decay indicates J = 1/2 or 3/2, even parity for the ground state of 11Be: see (AL71B). See also (TE77; theor.).

2. 9Be(t, p)11Be Qm = -1.167

Proton groups have been observed to many states of 11Be: see Table 11.2 (in PDF or PS) (PU62, AJ72A, AJ78A). The first excited state has an excitation energy of 319.8 ± 0.2 keV and τm = 0.18 ± 0.06 psec corresponding to a very strong E1 transition of 0.33 W.u. (HA71I). The Jπ of 11Be*(0.32) is 1/2-, as determined by a study of the yield of 320 keV γ-rays as a function of time in μ- capture by 11B (DE68L). The strength of the E1 transition fixes Jπ of 11Beg.s. to be 1/2+ or 3/2+, using the parity information obtained from the nature of the β- decay of the ground state [see reaction 1]. 11Be*(5.24, 6.71, 8.82) are strongly populated at Et = 20 MeV indicating that these states have a large overlap with 9Beg.s. + two neutrons (AJ72A).

3. 10Be(n, γ)11Be Qm = 0.503

See (75AJ02).

4. 10Be(d, p)11Be Qm = -1.722

Angular distributions of the p0 and p1 groups have been measured at Ed = 6 MeV (GO70: p1 only) and 12 MeV (AU70C): ln = 0 [and therefore Jπ = 1/2+ for 11Be(0)] and 1, S = 0.73 ± 0.06 and 0.63 ± 0.15, respectively (AU70C). At Ed = 25 MeV 11Be*(0, 0.32, 1.78) are strongly populated: S = 0.77, 0.96 and 0.50, respectively, Jπ = (5/2, 3/2)+ for 11Be*(1.78) [ln = 2] (ZW79).

5. 11Li(β-)11Be Qm = 20.76

See 11Li.

6. 11B(n, p)11Be Qm = -10.726

See 12B.

7. 13C(6Li, 8B)11Be Qm = -25.886

At E(6Li) = 80 MeV, 11Be*(0.32) is strongly populated and the angular distribution to this state has been measured (WE77A). 11Be*(2.69, 4.0) are also observed. It is suggested that these states have odd parity (WE76E) [see, however, reaction 2 for evidence concerning the positive parity of 11Be*(2.69)]. See also (WE77).
8. 14C(18O, 21Ne)11Be Qm = -12.206

See (BA74C).