
^{11}Be (2012KE01)(See 2 [Electromagnetic Transitions in A = 11] (in PDF or PS), 11.4 (in PDF or PS) and Energy Level Diagram for ^{11}Be and Isobar Diagram)
and μ = 1.6816 ± 0.0008 μ_{N} (1999GE18, 2000NE11), also see (2009FO01). R_{rms}^{charge} = 2.463 ± 0.015 fm from isotope shift measurements (2009NO02, 2010ZA02). Also see (2010PU01).
We accept the most precise measurement of the ^{11}Be mass M = 11.02166155 ± 0.00000062 u which yields a mass excess of 20177.60 ± 0.58 keV (2009RI03: TITAN). Other precise measurements have indicated ΔM = 20171 ± 4 keV (2005BB01: MINSTRAL), ΔM = 20170.1 ± 3.3 keV (2008BA18: MISTRAL) and ΔM = 20174.8 ± 3.6 keV (2009LU10: MISTRAL). These values compare with values measured in ^{9}Be(t, p): ΔM = 20175 ± 15 keV (1962PU01) and ^{10}Be(d, p): ΔM = 20174 ± 7 keV (1970GO11).
The halflife of ^{11}Be is 13.76 ± 0.07 sec; this is obtained from a weighted average of 13.81 ± 0.08 sec (1970AL21) and 13.57 ± 0.15 sec (1959WI49). The value 14.1 ± 0.3 sec has been reported by (1958NU40) who first identified ^{11}Be in the ^{11}B(n, p) reaction. Using T_{1/2} = 13.76 ± 0.07 sec and the branching ratio given in 11.29 (in PDF or PS) gives log ft = 6.826 ± 0.016 for decay to the ^{11}B ground state; see ^{11}B reaction 30 for further discussion on ^{11}B levels populated in ^{11}Be decay. The βdelayed alpha emission probability is 3.1 ± 0.4 % (1982MI08); see also (2011RA16). A discussion of βdelayed proton emission is given in (2011BA01) where a branching ratio of ≈ 3 × 10^{8} is estimated.
Complete kinematics were measured for charge exchange reactions on ^{1}H and ^{2}H targets at E(^{11}Li) = 64 MeV/A (1997SH12, 1997TE07, 1998SH06). The ^{11}Li_{g.s.} IAS state was identified at ^{11}Be*(21.16 ± 0.02) with Γ = 0.49 ± 0.07 MeV; this gives ΔE_{Coulomb} = 1.32 ± 0.02 MeV (1997TE07, 1998SH06). An Rmatrix analysis indicates the state decays mainly to ^{9}Li + p + n via the ^{10}Li + p channel. See (1991SU16) for more discussion on the isobaric analogue states of A = 11 nuclei.
The ^{11}Be(p, d)^{10}Be reaction was measured in inverse kinematics using an E(^{11}Be) = 35.3 MeV/A beam (1999FO09, 1999WI04, 2001WI05). The ^{10}Be*(0, 3.4, 6(multiplet)) states are populated. Coupled Channels DWBA analysis of the results indicate 16% core excitations for ^{11}Be_{g.s.}, i.e. [84% (0^{+} ⊗ s_{1/2})+16% (2^{+} ⊗ d_{5/2})]. See also (2000GO39, 2005TS03).
At E(^{11}Be) = 63.7 MeV/A elastic and inelastic scattering cross sections were measured up to E_{x} = 7 MeV (2004SH28). The ^{11}Be*(0 + 0.32) states were unresolved; analysis of quasielastic scattering data in a Continuum Discretized Coupled Channels (CDCC ) model reproduces the observations. Higher lying excited states are unbound, though measurement of the p + ^{10}Be particles permitted a construction of the ^{11}Be* scattering cross sections. A prominent peak corresponding to ^{11}Be*(1.78 [J^{π} = 5/2^{+}]) is observed, other unresolved states at ^{11}Be*(2.67, 3.41, 3.89, 3.96, 5.25) were included in the CDCC analysis. The calculations underpredict the inelastic data. It is suggested that ^{10}Be core deformation and excitations play a sizeable role in the ^{11}Be breakup process (2004SH28, 2007SU11, 2007SU17, 2008KE01). See (1997CO04, 1997CO11) for elastic scattering measurements at E(^{11}Be) = 49.3 MeV/A. Also see (2007CR04) for a theoretical analysis at E_{p} = 100 to 200 MeV.
Proton groups have been observed to the states displayed in 11.5 (in PDF or PS). The E = 320.04 ± 0.10 keV γray from the deexcitation of ^{11}Be*(0.32) was analyzed using the DSAM technique which indicates the mean lifetime τ_{m} = 166 ± 15 fs (1983MI08). This corresponds to B(E1) = 0.36 ± 0.03 W.u.. Also see (1997VO06).
At E(^{6}He) = 16.8 MeV angular distributions of α particles and complex α + fragment events were measured (2010MA29). ^{11}Be*(0, 0.32, 1.78, 2.69, ≈ 3.9, 5.24, 6.71, 8.82, 10.6) were populated. Analysis of the α + ^{6}He and α + ^{9, 10}Be data suggests that ^{11}Be*(10.6) likely ndecays to ^{10}Be excited states which subsequently decay to either α + ^{6}He or n + ^{9}Be. At E(^{6}He) = 25 MeV/A angular distributions of ^{10, 11}Be ions produced in the 1neutron and 2neutron transfer reactions were measured. The 1neutron transfer reaction cross section was found to be larger than the 2neutron transfer cross section, which is surprising since ^{6}He is a 2neutron halo nucleus (2003GE05). Also see ^{15}C in (1970AJ04).
Studies of ^{11}Be have been carried out via measurement of interaction cross sections and one neutron breakup cross sections, see 11.6 (in PDF or PS). The anomalously large cross sections observed can be related to the extent of the valence neutrons by various reaction models (1990LI39, 1991MU19, 1993FE02, 1993FE12, 1993MA25, 1995PE19, 1996AL13, 1997FO04, 1997YA07, 1999SE15, 2000BH09, 2000CA33, 2001LE21, 2002BR01, 2003CA07, 2006BH01). Measurements of the parallel and transverse momentum distributions of outgoing fragments can also be related to the extent of the neutron spatial distribution using the uncertainty principle, but details of the reaction mechanism and final state interactions influence the measurements (1992BE43, 1993BA64, 1994PO15, 1994SA30, 1995BA32, 1995ZA12, 1995ZA13, 1996BA40, 1996BA68, 1996CH38, 1996ES01, 1996HA29, 1996HE23, 1997RI04, 1998BA45, 1998BO01, 1998BO28, 1999FO13, 2000PA53, 2001ES05, 2003AB05, 2003CH65, 2004BE45). The measurements appear consistent with an R_{rms}^{matter} size of 2.73 ± 0.05 fm (2001OZ04) and a valence neutron "halo" that extends to R_{rms}^{halo} = 5.66 ± 0.20 fm (1988TA10). Overviews of the experimental work can be found in (1993KO11, 1994JO04, 1994MU14, 1995HA17, 1995JO09, 1997OR03, 1999KA67, 1999KN04, 2001OZ04, 2002BR01, 2005AU09). Also see theoretical analysis of diffraction dissociation, absorption and other relevant breakup mechanism effects (1993EV02, 1995EV01, 1996EV01, 1996VO04, 1999TO07, 2000BA47, 2000BO04, 2002CH60, 2002FA02, 2002MA26, 2002YA19, 2004AB29, 2004BO04, 2004CA50, 2004UE04, 2004WE04, 2005BA54, 2005BA72, 2005HO28, 2006MO03, 2006SU05). The complete kinematical detection of ^{10}Be + n following breakup on highZ targets provides a determination of the dipole strength distribution in the region just above the neutron binding threshold, but the nuclear breakup and higherorder Coulomb breakup components must be understood. See 11.6 (in PDF or PS) for a summary of ^{11}Be breakup measurements. At E(^{11}Be) = 68 MeV/A the nuclear and Coulomb breakup contributions on carbon and lead targets are analyzed by measuring the complete kinematics in ^{11}Be breakup (2004FU29). On the ^{nat}C target, the ^{11}Be*(1.78, 3.41) states are found to participate in the breakup reaction with L = 2 angular distributions; this implies J^{π} = 5/2^{+} and 3/2^{+} for these states, respectively. Further analysis and comparison with the breakup data from the ^{208}Pb target implies that at very forward angles the E1 Coulomb direct breakup mechanism is dominant. The dipole transition spectrum shows a strong peak near the neutron separation threshold, which is associated with the low neutron binding energy. The Pb target Coulomb breakup data with θ(^{11}Be) ≤ 1.3° were analyzed using ECIS; a neutron spectroscopic factor S = 0.72 ± 0.04 and Σ_{Ex < 4 MeV}B(E1) = 1.05 ± 0.06 e^{2} ⋅ fm^{2} were deduced. At E(^{11}Be) = 520 MeV/A a similar experiment was carried out (2003PA31); ^{10}Be + breakup neutrons and γrays from ^{10}Be*(3.37, 5.96, 6.26) were found in coincidence. In this case, S = 0.61 ± 0.05, Σ_{Ex < 4 MeV}B(E1) = 0.83 ± 0.06 e^{2} ⋅ fm^{2} and Σ_{Ex < 6.1 MeV}B(E1) = 0.90 ± 0.06 e^{2} ⋅ fm^{2} are deduced. See (1991HO06, 1994KI12, 1995BE26, 1995ES01, 1995IS02, 1995IS04, 1995SA32, 1996KA06, 1996KI04, 1997DE07, 1998BA45, 1999BA29, 1999DA02, 1999ME12, 2000CH27, 2001ME18, 2001SH21, 2001TY01, 2001TY02, 2002BA60, 2002CH60, 2002FA02, 2002MA26, 2002SU34, 2002ZA10, 2003BE54, 2003CA01, 2003CA25, 2003MA20, 2003TA06, 2004AB29, 2004ZA12, 2005BA72, 2005CA22, 2005IB01, 2006CA06, 2006GO05, 2007BL02, 2010OG02, 2011HA41) for theoretical analysis of the Coulomb dissociation mechanism and other issues related to the near threshold dipole strength distribution.
Spectroscopic factors of S = 0.42 ± 0.06 and 0.37 ± 0.06 were deduced for ^{11}Be(0 [J^{π} = 1/2^{+}]) and ^{11}Be*(0.32 [J^{π} = 1/2^{}]), respectively, from measurements at E(^{12}Be) = 78 MeV/A (2000NA23). The large s_{1/2} component in the ^{12}Be ground state appears to indicate that, in this case, N = 8 is not a good closed shell. A beam of 90 MeV/A ^{12}Be ions impinged on a ^{9}Be target where 1neutron knockout reactions populated ^{11}Be*(0, 1.778, 2.690, 3.949) (2011PE13). A kinematic energy reconstruction of the ^{10}Be + n products permitted an analysis of these states; decay modes and spectroscopic factors were analyzed and discussed. The state at 3949 keV decays evenly via neutron emission to the ^{10}Be*(0, 3.896) states, and the measured S_{n} = 80 ± 2 keV for feeding of the ^{10}Be*(3.896) state implies E_{x} = 3949 ± 2 keV (Γ < 40 keV).
At E(^{13}C) = 379 MeV, ^{11}Be*(0, 0.32, 1.78, 2.69, 3.96, 5.26, 5.90, 6.72, 8.82, (9.3), 10.73, 11.6, 13.6, 18.6, 21.5, 25.0) are populated (1998BO38, 1999BO26, 2002BO16, 2003BO24, 2003BO38). It is suggested, based on level spacing systematics, that the K = 3/2^{} molecular rotational band is built on ^{11}Be*(3.96 [J^{π} = 3/2^{}], 5.25 [5/2^{}], 6.72 [7/2^{}], 8.82 [9/2^{}], 10.80 [11/2^{}], 13.8 [13/2^{}], 18.6 [15/2^{}], 21.6 [17/2^{}], 25.0 [19/2^{}]). The moment of inertia deduced for the rotational system is consistent with a 2α3n structure with large deformation. Also see (1997VO06). Measurements for reaction (b) at E(^{14}N) = 217 MeV (2002BO16) populated ^{11}Be*(0, 0.32, 1.78, 2.69, 3.42, 3.92, 5.25, 5.98(4), 6.72, 8.82, 10.80, (11.75), 14.0) and reaction (c) at E(^{15}N) = 240 MeV (2002BO16) confirmed the presence of three new states at ^{11}Be*(10.8, 13.8, 21.6) that were reported in reaction (a).
An experiment measuring reaction (a) at E = 234 MeV was configured to detect the ^{14}O ejectile momenta in coincidence with the ^{10}Be decay recoil from ^{11}Be* neutron decay in order to determine neutron decay widths for excited ^{11}Be states (2009HA01, 2010FR03). Neutron unbound levels at ^{11}Be*(1.78, 2.69, (3.41), 3.96, 5.24, 5.96, 6.72, 7.10, 8.82, 10.70) are observed and decay branching ratios are reported, see 11.7 (in PDF or PS). The branching ratios are in poor agreement with those indicated in ^{11}Li decay to ^{11}Be states. A rotational band based on ^{11}Be*(3.96 [J^{π} = 3/2^{}], 5.24 [5/2^{}], 6.72 [7/2^{}]) is suggested with further indications that the E_{x} = 8.82 MeV may also form a 3/2^{} molecular cluster bandhead. The angular distributions of E_{x} < 4 MeV states populated in reactions (a) at E(^{16}O) = 233.5 MeV: ^{11}Be*(0.32, 1.78, 3.96), (b) at E(^{14}N) = 217 MeV: ^{11}Be*(0, 0.32, 1.78, 2.69, 3.41) and (c) at E(^{12}C) = 230.7 MeV: ^{11}Be*(0.32, 2.7, 3.90) (2003BO24, 2003BO38, 2004BO12) are analyzed in an attempt to resolve the discrepancy in the J^{π} assignments for ^{11}Be*(3.41, 3.90, 3.96). Reactions (a) and (c) have a common property which is that the angular momentum transferred to the target is l_{t} = 0. In the 2neutron transfer reaction (a) the angular distribution of ^{11}Be*(3.96) is consistent with l_{t} = 2, 0, which is consistent with J^{π} = 3/2^{} and in agreement with the results from reaction ^{9}Be(t, p) (1990LI19). In the twoproton pickup reaction (c) the angular distributions of ^{11}Be*(2.7, 3.90) are inphase, which indicates similar (negative) parity for the two states. Systematics described, for example, in (2001MI29) indicate that 3/2^{+} and 5/2^{} states should be present near this excitation energy leading to conjecture that ^{11}Be*(3.41, 3.90) have J^{π} = 3/2^{+} and 5/2^{}, respectively (2003BO24, 2003BO38, 2004BO12). See 11.8 (in PDF or PS) for an overview of analysis of J^{π} values in this region, also see (2005FO01, 2011FO07).
Neutron unbound states in ^{11}Be were populated in the fragmentation of ^{48}Ca on a ^{9}Be target at E(^{48}Ca) = 60 MeV/A (2008CH07). The excited states near 4 MeV were observed in the kinematic reconstruction of coincident neutron plus ^{10}Be ejectiles; the decays populated ^{10}Be*(3.368). A fit including two known Γ < 10 keV resonances at ^{11}Be*(3.887, 3.956), from E_{res} = 19 ± 15 keV and 84 ± 15 keV, reproduced the data; however the data were also reasonably well fit with a single resonance at E_{res} = 30 keV with Γ = 65 keV.
The thermal neutron capture cross section is < 1 mb (see (1975AJ02)). Also see (2004LI04, 2005LI32) who use the Asymptotic Normalization Coefficient method to determine σ(E_{n}) for E = 0 to 1 MeV.
An ab initio nocore shell model was used to calculate the binding energies for the lowest J^{π} = 1/2^{+} and 1/2^{} states in ^{11}Be and the n + ^{10}Be phase shifts (2008QU03, 2009QU02).
Angular distributions have been measured at E_{d} = 6 MeV (1970GO11: p_{1}). At E_{d} = 12 MeV (1970AU02) p_{0} is populated with l_{n} = 0 [and therefore J^{π} = 1/2^{+} for ^{11}Be_{g.s.}] and p_{1} is populated with l = 1; S = 0.73 ± 0.06 and 0.63 ± 0.15, respectively (1970AU02). At E_{d} = 25 MeV ^{11}Be*(0, 0.32, 1.78) are strongly populated: S = 0.77, 0.96, 0.50, respectively, J^{π} = (5/2, 3/2)^{+} for ^{11}Be*(1.78) [l_{n} = 2] (1979ZW01). Also see the analyses of (1999TI04, 2004KE08, 2009DE15, 2009MO39).
The betadecay of ^{11}Li populates ^{11}Be*(0, 0.32) and higherlying neutron unbound ^{11}Be states that γ, n, d, t, α and ^{6}He decay. The beta delayed 1neutron emission branching ratio is %β1n = 86.2 ± 0.9, which is deduced using I_{γ}(^{11}Be*(0.32 → 0)) = 7.7 ± 0.8 % (2005HI03), P_{2n}/P_{1n} = 0.048 ± 0.005 and P_{3n}/P_{1n} = 0.022 ± 0.002 (1980AZ01). Also see (1974RO31, 1980AZ01, 1980DE39, 1981BJ01, 1997BO01) for %βn values based on different I_{γ}(^{11}Be*(0.32 → 0)) values; notably I_{γ}(^{11}Be*(0.32 → 0)) = 6.3 ± 0.6 % (1997BO01) implies %β1n = 87.6 ± 0.8. The data related to states involved in neutron emission have ambiguous interpretation connected with uncertainty in placement of neutron decay branches; the observed decay γray intensities from reported measurements are also in poor agreement (see 11.9 (in PDF or PS)). See (1977BA11, 1994JO04, 1994SU12, 1995OH02, 1995ZH31, 1996SU23, 1997SU12, 2001KA31, 2002KA44, 2003SU04, 2003SU28) for theoretical discussion. The measurements of (1997MO35) utilized βγ and βn coincidence data to deduce the branching ratios populating ^{11}Be and ^{10}Be states, while (1997AO01, 1997AO04) obtained βγ, βn and βnγ coincidence data in their measurements. Similar γray and neutron energy spectra were observed by each experimenter, however the evaluation of the βnγ triple coincidence data of (1997AO01, 1997AO04) required a new, previously unobserved level at ^{11}Be*(8.03 ± 0.05) that populates ^{10}Be*(5.958, 6.179). This observation indicated a significantly different interpretation of the ^{11}Li decay scheme than in previous evaluations such as (1990AJ01). In (2003FY01, 2004FY01), Doppler Broadened Line shape Analysis (DBLA) of ^{10}Be γray lines, was used to determine the excitation energy of parent states in ^{11}Be. A rigorous analysis of the line shape of emitted γrays yields details on the lifetime of ^{10}Be states populated in βdelayed neutron emission and on the recoil velocity of ^{10}Be atoms, which is connected to the energy of the emitted neutrons and therefore to the ^{11}Be parent level energy; this analysis also depends on the stopping power of the implantation medium. Analysis given in (2003FY01) supports the interpretation of (1997AO01, 1997AO04), but they suggest that the observed ^{11}Be*(8.03) branch corresponds to decay from the known level ^{11}Be*(8.82) with T_{1/2} = 61 ± 18 fs to ^{10}Be*(5.958). In (2004FY01) γray transitions corresponding to ^{10}Be*(5.958 → 0) and ^{10}Be*(6.263 → 3.368) were observed for the first time in ^{11}Li decay, and a more complete DBLA analysis is given for branches that populate ^{10}Be*(3.368, 5.958, 5.960, 6.179, 6.263); see 11.10 (in PDF or PS). The 8π spectrometer at TRIUMFISAC measured γrays from ^{11}Li decay (2004SA46). Improved γray decay branching ratios were obtained for the levels of ^{10}Be. A DBLA analysis was performed, see 11.11 (in PDF or PS). The high efficiency and resolution of the detector array provided sufficient information to confirm participation of both ^{11}Be*(8.03, 8.81) in the decay of ^{11}Li. Finally, βγ, βn and βnγ coincidence data were measured in the decay of polarized ^{11}Li atoms (2004HI12, 2005HI03); see 11.12 (in PDF or PS) and 11.13 (in PDF or PS). In the βn and βγ coincidence measurements, the β asymmetry unambiguously determined the spins and parities of ^{11}Be levels populated in the decay, and the asymmetry was used to resolve the origins of overlapping peaks in the delayed neutron energy spectrum. Although serious conflicts remain amongst the present measurements, the results of (2004HI12, 2004HI24, 2005HI03) are based on the most rigorous set of βasymmetry plus βnγ coincidence constraints; see Fig. 3. More complex contributions to the ^{11}Li decay scheme are associated with weak population of higher lying ^{11}Be states. βdelayed α and triton emission from ^{11}Be*(10.6, 18.5) were first reported in (1981LA11, 1984LA27). A summary of βdelayed particle emission measurements is given in 11.14 (in PDF or PS) and Fig. 3. The state at ^{11}Be*(18.15) is a candidate for having a ^{9}Li + d "halo" structure analogous to the ^{9}Li + 2n structure of the ^{11}Li_{g.s.} (1995ZH31), and the strong feeding of the state in βdecay implies a large overlap with ^{11}Li_{g.s.} (1996MU19, 1997MU06). After the discovery of the ^{11}Li halo, investigation of possible ^{11}Li decay directly to the ^{9}Li + d continuum received special attention, since it could be sensitive to the ^{11}Li halo (1991BO31, 1995OH02, 1996MU19, 1997MU06, 1997RI04) and might indicate the presence of a deuteronhalo state in ^{11}Be (1995ZH31, 2004KU27); however the analysis of (1997BO03) provided no conclusive evidence to support this decay mode. Also see (2008RA23). See (2010KA06) for an analysis of GT transitions in ^{11}Li βdecay.
At E_{e} = 200 MeV, photopion production on ^{11}B populates states listed in 11.15 (in PDF or PS). A PWIA analysis of measured differential cross sections was used to deduce spinflip charge exchange E1 strengths (1995YA01).
The time dependence of μ^{} capture from the hyperfine levels of muonic^{11}B leading to ^{11}Be*(0.32) determined J^{π} = 1/2^{} for that state (1968DE20). The ratio of the capture cross section from the hyperfine levels to ^{11}Be*(0.32) can also be related to the ratio of the induced pseudoscalar to axial vector form factor, g_{p}/g_{A} = 4.3^{+2.8}_{4.3} (stat.) ± 0.5 (sys.) (1998WI26, 2002WI02); this agrees with partial conservation of the axial current. Also see (1998MU17).
The ^{11}B(μ^{}, ν)^{11}Be(1/2^{}) capture reaction is sensitive to the pseudoscalar coupling constant, g_{p}; see discussion in (1994KU32, 1995KU35).
The photon spectrum from stopped pion capture on ^{11}B includes a peak corresponding to ^{11}Be*(0 + 0.32) (1986PE05).
The cross section has been measured for E_{n} = 14 MeV (2001KAZY) and E_{n} = 14 to 16.9 MeV; see references in (1975AJ02), and see ^{12}B. At E_{n} = 96 MeV, angular dependent cross sections were measured for θ < 30° (2001RI02). A DWBA analysis was used to deduce the GT strength distribution, and a multipole decomposition was used to analyze the data up to E_{x} = 35 MeV; while a broad ΔL = 0 peak is observed near E_{x} = 9 MeV, the higher excitation spectrum is dominated by a ΔL = 1 peak at E_{x} = 12 MeV.
At E_{d} = 70 MeV angular distributions of cross section and analyzing power were measured and GT transitions populating ^{11}Be*(0.3, 2.7, 3.8) were identified with J^{π} = 1/2^{}, (3/2^{}) and (5/2^{}), respectively (1993SA09, 1994SA11); a broad bump at E_{x} ≈ 10 MeV (Γ ≈ 7 MeV) apparently having ΔL = 1 is suggested as a spinflip dipole transition. At E_{d} = 270 MeV angular distributions of cross section and analyzing power were measured (2001OH07). Peaks corresponding to ^{11}Be*(0.32, 2.7, 3.9, (5.4), 6.3, (7.3), 8.2, 9.2, (10.2), 11.6, (13.2)) were evaluated in a DWBA analysis to identify GT, spin and isospin flip dipole transitions. The states at E_{x} = 0.3, 2.7, 3.9, 5.4, 7.3, 8.2 MeV were found to have GT character.
At E_{t} = 127 MeV, the cross sections for populating ^{11}Be*(0.32, 2.69, 3.89, 8.94) were measured at 0°, and B(GT) = 0.23 ± 0.05, 0.17 ± 0.05, 0.07 ± 0.03 values were deduced for ^{11}Be*(0.32 [J^{π} = 1/2^{}], 2.69 [(3/2^{})], 3.89 [(5/2^{})]), respectively (1998DA05).
At E(^{7}Li) = 57 MeV, the chargeexchange reaction on ^{11}B populated states shown in 11.16 (in PDF or PS) (2001CA45). The measurements were at θ ≤ 35° and the experimental resolution separated ^{7}Be and ^{7}Be*(0.429). Results were compared with QRPA calculations. A subsequent analysis of the data indicated a resonance at E_{x} = 9.4 ± 0.5 MeV with Γ = 7.0 ± 0.5 MeV (2004CA29).
A study of muon induced backgrounds in large volume scintillators measured σ(100 MeV) < 1.22 μb and σ(190 MeV) < 2.34 μb for production of ^{11}Be (2000HA33). See (2010AB05) for analysis of production rates in the KamLAND detector.
Proton emission following pion π^{} capture on ^{12}C was measured at E_{π} = 145 MeV (1987BL07). Also see (1975CO06: E_{π} = 27 MeV), (1977JA15: E_{π} = 60, 100, 200 MeV), (1977AB09: E_{π} = 1.43 GeV/c), (1975CO06, 1980MC03, 1981MC09: E_{π} = 100, 160, 220 MeV), (1980KA13, 1981AN14: E_{π} = 40 GeV/c), (1981KA43: E_{π} = 400, 475 MeV), and (1976DE39, 1978DE30, 1979ME07, 1979SC02, 1981PR02: E_{π} = stopped).
At E(^{7}Li) = 82 to 83 MeV, groups corresponding to ^{11}Be*(0 + 0.32, 1.8, 3.4) are reported by (1982AL08, 1983AL20).
Angular distributions of quasielastic scattering of ^{11}Be on ^{1}H and ^{12}C targets were measured at E(^{11}Be) = 38.4 MeV/A (2008LA01). The results are interpreted as purely elastic scattering since population of ^{11}Be* is expected to be two orders of magnitude smaller than elastic scattering. The impact of the weak binding energy on the interaction potentials was studied. While data on the ^{1}H target was reasonably reproduced by reducing the real part of the potential, the ^{12}C target data required modifications to the socalled "Virtual Coupling Potential" and requires further measurements to determine the dependency on coupling to excited states and the continuum. Earlier unpublished work from GANIL is discussed in (1997AL05, 1997JO16, 1998TO05, 2000JO21, 2002BO25, 2002TA31, 2003AB05, 2003TA04, 2005BA72, 2005TA34). Also see analysis in (1995EV01, 1996EV01, 1996VO04, 1999BR09, 1999FO13, 2000BO45, 2002AL25, 2002SU18, 2009HA18).
Neutron removal cross sections were measured at E(^{12}Be) = 39.3 MeV/A. States at ^{11}Be*(0, 0.32, 1.78, 2.69, ≈ 4) were populated (2005PA68, 2006PA04). The spectroscopic factors S = 0.56 ± 0.18, 0.44 ± 0.08, 0.48 ± 0.06, 0.40 ± 0.07 were deduced for the first four states, respectively. The significant feeding of ^{11}Be*(1.78 [J^{π} = 5/2^{+}]) implies a ν(0d_{5/2})^{2} component in the ^{12}Be_{g.s.}.
At E(^{6}Li) = 80 MeV, ^{11}Be*(0.32) is strongly populated and the angular distribution to this state has been measured; ^{11}Be*(2.69, 4.0) are also observed (1977WE03). It is suggested that these states have odd parity (1977WE1B; thesis); however, see (1972AJ01): ^{9}Be(t, p)^{11}Be where positive parity was deduced for ^{11}Be*(2.69).
At E(^{18}O) = 88.7 MeV, ^{11}Be*(0 + 0.32) appear to be involved in the reaction which populates ^{21}Ne(0, 0.35, 1.75, 2.87, 4.43, 6.45) (1974BA15).
Elastic and quasielastic scattering angular distributions were measured for 10° ≤ θ ≤ 110° at E_{cm} = 24.5 MeV ^{9, 10, 11}Be on 5501000 μg/cm^{2} targets using a large solid angle ΔEE Si detector array (2010DI08, 2010SC12). Comparison of the angular distributions reveals a significant reduction of the socalled "Coulombnuclear interference peak" for ^{11}Be at θ_{cm} ≈ 40 degrees. An optical model analysis indicates the interference peak is suppressed by absorption, related to the diffuse halo. A total reaction cross section of σ_{R} = 2730 mb is deduced for ^{11}Be, compared with σ_{R} = 1090 and 1260 mb for ^{9, 10}Be, respectively; a sizeable ^{10}Be breakup component from ^{11}Be reactions indicates that about 40% of the ^{11}Be total reaction σ is attributed to transfer and/or breakup reactions.
The ^{11}Be*(0, 0.32 MeV) quasielastic scattering angular distributions were measured in a large solid angle ΔEE Si detector array for reactions on a 3.5 mg/cm^{2} ^{120}Sn target at E = 32 MeV, which is just above the Coulomb barrier energy (2009AC02). In the angular range 15° ≤ θ ≤ 38°, the scattering events were separated from the breakup events via ΔEE reaction product identification, while for 52° ≤ θ ≤ 86° the ^{10}Be ejectiles were not distinguishable from the ^{11}Be events. The angular distribution has a "pronounced deviation from the typical Fresneltype scattering," and the Coulombnuclear interference appears strongly damped. Coupled Channels calculations suggest that couplings to the pstates just above the breakup threshold may be important.
Coulomb excitation measurements populating ^{11}Be*(0.32) have been carried out and the resulting B(E1) values are displayed in 11.17 (in PDF or PS). These compare with 0.116 ± 0.012 e^{2} ⋅ fm^{2} deduced from lifetime measurements. Also see (1995BE26, 1995BE47, 1995TY01, 1997AN01, 1997AN18, 1997DE07, 1997NA19, 2003BE54, 2003TA06, 2004TY01, 2005BA72, 2005TY02, 2007BE54, 2008ES04).
The elastic scattering angular distributions were measured for E(^{11}Be) = 40 MeV (2006MA51) and E(^{11}Be) = 40 to 48 MeV (2007MA90). Results are compared with ^{9}Be elastic scattering on ^{209}Bi. Near the Coulomb barrier the ^{11}Be cross sections are larger than the ^{9}Be cross sections, but at higher energies they become more similar, suggesting that direct processes related to the halo structure are more relevant at nearbarrier energies.
Fusion cross sections were measured for ^{209}Bi + ^{11}Be at E(^{11}Be) = 30 to 70 MeV (1995YO03, 1996YO08) and E(^{11}Be) = 35 to 50 MeV (1998SI16, 1998SI38). At E(^{11}Be) = 35 to 68 MeV fusion cross sections were measured for ^{11}Be + ^{238}U (1995FE02, 1997FE08, 1999FE12). Also see (1995IM01, 1997SI07, 1997SI25, 1997ZA04, 1999DA02, 1999PE07, 2000HA14, 2000WA37, 2002AL12, 2002DI02, 2002SI07, 2002VI12, 2003BB07, 2003YA17, 2004DI16, 2005LI64).
