(See Table 11.4 (in PDF or PS) and Energy Level Diagram for 11Be and Isobar Diagram)
We accept the most precise measurement of the 11Be 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 9Be(t, p): ΔM = 20175 ± 15 keV (1962PU01) and 10Be(d, p): ΔM = 20174 ± 7 keV (1970GO11).
The half-life of 11Be 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 11Be in the 11B(n, p) reaction. Using T1/2 = 13.76 ± 0.07 sec and the branching ratio given in Table 11.29 (in PDF or PS) gives log ft = 6.826 ± 0.016 for decay to the 11B ground state; see 11B reaction 30 for further discussion on 11B levels populated in 11Be decay. The β-delayed alpha emission probability is 3.1 ± 0.4 % (1982MI08); see also (2011RA16). A discussion of β-delayed proton emission is given in (2011BA01) where a branching ratio of ~ 3 x 10-8 is estimated.
Complete kinematics were measured for charge exchange reactions on 1H and 2H targets at E(11Li) = 64 MeV/A (1997SH12, 1997TE07, 1998SH06). The 11Lig.s. IAS state was identified at 11Be*(21.16 ± 0.02) with Γ = 0.49 ± 0.07 MeV; this gives ΔECoulomb = 1.32 ± 0.02 MeV (1997TE07, 1998SH06). An R-matrix analysis indicates the state decays mainly to 9Li + p + n via the 10Li + p channel. See (1991SU16) for more discussion on the isobaric analogue states of A = 11 nuclei.
The 11Be(p, d)10Be reaction was measured in inverse kinematics using an E(11Be) = 35.3 MeV/A beam (1999FO09, 1999WI04, 2001WI05). The 10Be*(0, 3.4, 6(multiplet)) states are populated. Coupled Channels DWBA analysis of the results indicate 16% core excitations for 11Beg.s., i.e. [84% (0+ ⊗ s1/2)+16% (2+ ⊗ d5/2)]. See also (2000GO39, 2005TS03).
At E(11Be) = 63.7 MeV/A elastic and inelastic scattering cross sections were measured up to Ex = 7 MeV (2004SH28). The 11Be*(0 + 0.32) states were unresolved; analysis of quasi-elastic scattering data in a Continuum Discretized Coupled Channels (CDCC ) model reproduces the observations. Higher lying excited states are unbound, though measurement of the p + 10Be particles permitted a construction of the 11Be* scattering cross sections. A prominent peak corresponding to 11Be*(1.78 [Jπ = 5/2+]) is observed, other unresolved states at 11Be*(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 10Be core deformation and excitations play a sizeable role in the 11Be breakup process (2004SH28, 2007SU11, 2007SU17, 2008KE01). See (1997CO04, 1997CO11) for elastic scattering measurements at E(11Be) = 49.3 MeV/A. Also see (2007CR04) for a theoretical analysis at Ep = 100 to 200 MeV.
Proton groups have been observed to the states displayed in Table 11.5 (in PDF or PS). The E = 320.04 ± 0.10 keV γ-ray from the deexcitation of 11Be*(0.32) was analyzed using the DSAM technique which indicates the mean lifetime τm = 166 ± 15 fs (1983MI08). This corresponds to B(E1) = 0.36 ± 0.03 W.u.. Also see (1997VO06).
At E(6He) = 16.8 MeV angular distributions of α particles and complex α + fragment events were measured (2010MA29). 11Be*(0, 0.32, 1.78, 2.69, ~ 3.9, 5.24, 6.71, 8.82, 10.6) were populated. Analysis of the α + 6He and α + 9, 10Be data suggests that 11Be*(10.6) likely n-decays to 10Be excited states which subsequently decay to either α + 6He or n + 9Be.
At E(6He) = 25 MeV/A angular distributions of 10, 11Be ions produced in the 1-neutron and 2-neutron transfer reactions were measured. The 1-neutron transfer reaction cross section was found to be larger than the 2-neutron transfer cross section, which is surprising since 6He is a 2-neutron halo nucleus (2003GE05). Also see 15C in (1970AJ04).
Studies of 11Be have been carried out via measurement of interaction cross sections and one neutron breakup cross sections, see Table 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 Rrmsmatter size of 2.73 ± 0.05 fm (2001OZ04) and a valence neutron "halo" that extends to Rrmshalo = 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 10Be + n following breakup on high-Z targets provides a determination of the dipole strength distribution in the region just above the neutron binding threshold, but the nuclear breakup and higher-order Coulomb breakup components must be understood. See Table 11.6 (in PDF or PS) for a summary of 11Be breakup measurements.
At E(11Be) = 68 MeV/A the nuclear and Coulomb breakup contributions on carbon and lead targets are analyzed by measuring the complete kinematics in 11Be breakup (2004FU29). On the natC target, the 11Be*(1.78, 3.41) states are found to participate in the breakup reaction with L = 2 angular distributions; this implies Jπ = 5/2+ and 3/2+ for these states, respectively. Further analysis and comparison with the breakup data from the 208Pb 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(11Be) ≤ 1.3° were analyzed using ECIS; a neutron spectroscopic factor S = 0.72 ± 0.04 and ΣEx < 4 MeVB(E1) = 1.05 ± 0.06 e2 ⋅ fm2 were deduced. At E(11Be) = 520 MeV/A a similar experiment was carried out (2003PA31); 10Be + breakup neutrons and γ-rays from 10Be*(3.37, 5.96, 6.26) were found in coincidence. In this case, S = 0.61 ± 0.05, ΣEx < 4 MeVB(E1) = 0.83 ± 0.06 e2 ⋅ fm2 and ΣEx < 6.1 MeVB(E1) = 0.90 ± 0.06 e2 ⋅ fm2 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 11Be(0 [Jπ = 1/2+]) and 11Be*(0.32 [Jπ = 1/2-]), respectively, from measurements at E(12Be) = 78 MeV/A (2000NA23). The large s1/2 component in the 12Be ground state appears to indicate that, in this case, N = 8 is not a good closed shell.
A beam of 90 MeV/A 12Be ions impinged on a 9Be target where 1-neutron knockout reactions populated 11Be*(0, 1.778, 2.690, 3.949) (2011PE13). A kinematic energy reconstruction of the 10Be + 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 10Be*(0, 3.896) states, and the measured Sn = 80 ± 2 keV for feeding of the 10Be*(3.896) state implies Ex = 3949 ± 2 keV (Γ < 40 keV).
At E(13C) = 379 MeV, 11Be*(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 11Be*(3.96 [Jπ = 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 2α-3n structure with large deformation. Also see (1997VO06).
Measurements for reaction (b) at E(14N) = 217 MeV (2002BO16) populated 11Be*(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(15N) = 240 MeV (2002BO16) confirmed the presence of three new states at 11Be*(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 14O ejectile momenta in coincidence with the 10Be decay recoil from 11Be* neutron decay in order to determine neutron decay widths for excited 11Be states (2009HA01, 2010FR03). Neutron unbound levels at 11Be*(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 Table 11.7 (in PDF or PS). The branching ratios are in poor agreement with those indicated in 11Li decay to 11Be states. A rotational band based on 11Be*(3.96 [Jπ = 3/2-], 5.24 [5/2-], 6.72 [7/2-]) is suggested with further indications that the Ex = 8.82 MeV may also form a 3/2- molecular cluster bandhead.
The angular distributions of Ex < 4 MeV states populated in reactions (a) at E(16O) = 233.5 MeV: 11Be*(0.32, 1.78, 3.96), (b) at E(14N) = 217 MeV: 11Be*(0, 0.32, 1.78, 2.69, 3.41) and (c) at E(12C) = 230.7 MeV: 11Be*(0.32, 2.7, 3.90) (2003BO24, 2003BO38, 2004BO12) are analyzed in an attempt to resolve the discrepancy in the Jπ assignments for 11Be*(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 lt = 0. In the 2-neutron transfer reaction (a) the angular distribution of 11Be*(3.96) is consistent with lt = 2, 0, which is consistent with Jπ = 3/2- and in agreement with the results from reaction 9Be(t, p) (1990LI19). In the two-proton pickup reaction (c) the angular distributions of 11Be*(2.7, 3.90) are in-phase, 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 11Be*(3.41, 3.90) have Jπ = 3/2+ and 5/2-, respectively (2003BO24, 2003BO38, 2004BO12). See Table 11.8 (in PDF or PS) for an overview of analysis of Jπ values in this region, also see (2005FO01, 2011FO07).
Neutron unbound states in 11Be were populated in the fragmentation of 48Ca on a 9Be target at E(48Ca) = 60 MeV/A (2008CH07). The excited states near 4 MeV were observed in the kinematic reconstruction of coincident neutron plus 10Be ejectiles; the decays populated 10Be*(3.368). A fit including two known Γ < 10 keV resonances at 11Be*(3.887, 3.956), from Eres = 19 ± 15 keV and 84 ± 15 keV, reproduced the data; however the data were also reasonably well fit with a single resonance at Eres = 30 keV with Γ = 65 keV.
Angular distributions have been measured at Ed = 6 MeV (1970GO11: p1). At Ed = 12 MeV (1970AU02) p0 is populated with ln = 0 [and therefore Jπ = 1/2+ for 11Beg.s.] and p1 is populated with l = 1; S = 0.73 ± 0.06 and 0.63 ± 0.15, respectively (1970AU02). At Ed = 25 MeV 11Be*(0, 0.32, 1.78) are strongly populated: S = 0.77, 0.96, 0.50, respectively, Jπ = (5/2, 3/2)+ for 11Be*(1.78) [ln = 2] (1979ZW01). Also see the analyses of (1999TI04, 2004KE08, 2009DE15, 2009MO39).
The beta-decay of 11Li populates 11Be*(0, 0.32) and higher-lying neutron unbound 11Be states that γ, n, d, t, α and 6He decay. The beta delayed 1-neutron emission branching ratio is %β-1n = 86.2 ± 0.9, which is deduced using Iγ(11Be*(0.32 → 0)) = 7.7 ± 0.8 % (2005HI03), P2n/P1n = 0.048 ± 0.005 and P3n/P1n = 0.022 ± 0.002 (1980AZ01). Also see (1974RO31, 1980AZ01, 1980DE39, 1981BJ01, 1997BO01) for %β-n values based on different Iγ(11Be*(0.32 → 0)) values; notably Iγ(11Be*(0.32 → 0)) = 6.3 ± 0.6 % (1997BO01) implies %β-1n = 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 γ-ray intensities from reported measurements are also in poor agreement (see Table 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 β-γ and β-n coincidence data to deduce the branching ratios populating 11Be and 10Be states, while (1997AO01, 1997AO04) obtained β-γ, β-n and β-n-γ coincidence data in their measurements. Similar γ-ray and neutron energy spectra were observed by each experimenter, however the evaluation of the β-n-γ triple coincidence data of (1997AO01, 1997AO04) required a new, previously unobserved level at 11Be*(8.03 ± 0.05) that populates 10Be*(5.958, 6.179). This observation indicated a significantly different interpretation of the 11Li decay scheme than in previous evaluations such as (1990AJ01).
In (2003FY01, 2004FY01), Doppler Broadened Line shape Analysis (DBLA) of 10Be γ-ray lines, was used to determine the excitation energy of parent states in 11Be. A rigorous analysis of the line shape of emitted γ-rays yields details on the lifetime of 10Be states populated in β-delayed neutron emission and on the recoil velocity of 10Be atoms, which is connected to the energy of the emitted neutrons and therefore to the 11Be 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 11Be*(8.03) branch corresponds to decay from the known level 11Be*(8.82) with T1/2 = 61 ± 18 fs to 10Be*(5.958). In (2004FY01) γ-ray transitions corresponding to 10Be*(5.958 → 0) and 10Be*(6.263 → 3.368) were observed for the first time in 11Li decay, and a more complete DBLA analysis is given for branches that populate 10Be*(3.368, 5.958, 5.960, 6.179, 6.263); see Table 11.10 (in PDF or PS).
The 8π spectrometer at TRIUMF-ISAC measured γ-rays from 11Li decay (2004SA46). Improved γ-ray decay branching ratios were obtained for the levels of 10Be. A DBLA analysis was performed, see Table 11.11 (in PDF or PS). The high efficiency and resolution of the detector array provided sufficient information to confirm participation of both 11Be*(8.03, 8.81) in the decay of 11Li.
Finally, β-γ, β-n and β-n-γ coincidence data were measured in the decay of polarized 11Li atoms (2004HI12, 2005HI03); see Tables 11.12 (in PDF or PS) and 11.13 (in PDF or PS). In the β-n and β-γ coincidence measurements, the β asymmetry unambiguously determined the spins and parities of 11Be 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 β-asymmetry plus β-n-γ coincidence constraints; see Fig. 3.
More complex contributions to the 11Li decay scheme are associated with weak population of higher lying 11Be states. β-delayed α and triton emission from 11Be*(10.6, 18.5) were first reported in (1981LA11, 1984LA27). A summary of β-delayed particle emission measurements is given in Table 11.14 (in PDF or PS) and Fig. 3.
The state at 11Be*(18.15) is a candidate for having a 9Li + d "halo" structure analogous to the 9Li + 2n structure of the 11Lig.s. (1995ZH31), and the strong feeding of the state in β-decay implies a large overlap with 11Lig.s. (1996MU19, 1997MU06). After the discovery of the 11Li halo, investigation of possible 11Li decay directly to the 9Li + d continuum received special attention, since it could be sensitive to the 11Li halo (1991BO31, 1995OH02, 1996MU19, 1997MU06, 1997RI04) and might indicate the presence of a deuteron-halo state in 11Be (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 G-T transitions in 11Li β-decay.
At Ee = 200 MeV, photo-pion production on 11B populates states listed in Table 11.15 (in PDF or PS). A PWIA analysis of measured differential cross sections was used to deduce spin-flip charge exchange E1 strengths (1995YA01).
The time dependence of μ- capture from the hyperfine levels of muonic-11B leading to 11Be*(0.32) determined Jπ = 1/2- for that state (1968DE20). The ratio of the capture cross section from the hyperfine levels to 11Be*(0.32) can also be related to the ratio of the induced pseudoscalar to axial vector form factor, gp/gA = 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 photon spectrum from stopped pion capture on 11B includes a peak corresponding to 11Be*(0 + 0.32) (1986PE05).
The cross section has been measured for En = 14 MeV (2001KAZY) and En = 14 to 16.9 MeV; see references in (1975AJ02), and see 12B. At En = 96 MeV, angular dependent cross sections were measured for θ < 30° (2001RI02). A DWBA analysis was used to deduce the G-T strength distribution, and a multipole decomposition was used to analyze the data up to Ex = 35 MeV; while a broad ΔL = 0 peak is observed near Ex = 9 MeV, the higher excitation spectrum is dominated by a ΔL = 1 peak at Ex = 12 MeV.
At Ed = 70 MeV angular distributions of cross section and analyzing power were measured and G-T transitions populating 11Be*(0.3, 2.7, 3.8) were identified with Jπ = 1/2-, (3/2-) and (5/2-), respectively (1993SA09, 1994SA11); a broad bump at Ex ~ 10 MeV (Γ ~ 7 MeV) apparently having ΔL = 1 is suggested as a spin-flip dipole transition. At Ed = 270 MeV angular distributions of cross section and analyzing power were measured (2001OH07). Peaks corresponding to 11Be*(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 G-T, spin and isospin flip dipole transitions. The states at Ex = 0.3, 2.7, 3.9, 5.4, 7.3, 8.2 MeV were found to have G-T character.
At Et = 127 MeV, the cross sections for populating 11Be*(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 11Be*(0.32 [Jπ = 1/2-], 2.69 [(3/2-)], 3.89 [(5/2-)]), respectively (1998DA05).
At E(7Li) = 57 MeV, the charge-exchange reaction on 11B populated states shown in Table 11.16 (in PDF or PS) (2001CA45). The measurements were at θ ≤ 35° and the experimental resolution separated 7Be and 7Be*(0.429). Results were compared with QRPA calculations. A subsequent analysis of the data indicated a resonance at Ex = 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 11Be (2000HA33). See (2010AB05) for analysis of production rates in the KamLAND detector.
Proton emission following pion π- capture on 12C was measured at Eπ- = 145 MeV (1987BL07). Also see (1975CO06: Eπ- = 27 MeV), (1977JA15: Eπ- = 60, 100, 200 MeV), (1977AB09: Eπ- = 1.43 GeV/c), (1975CO06, 1980MC03, 1981MC09: Eπ- = 100, 160, 220 MeV), (1980KA13, 1981AN14: Eπ = 40 GeV/c), (1981KA43: Eπ- = 400, 475 MeV), and (1976DE39, 1978DE30, 1979ME07, 1979SC02, 1981PR02: Eπ- = stopped).
Angular distributions of quasi-elastic scattering of 11Be on 1H and 12C targets were measured at E(11Be) = 38.4 MeV/A (2008LA01). The results are interpreted as purely elastic scattering since population of 11Be* 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 1H target was reasonably reproduced by reducing the real part of the potential, the 12C target data required modifications to the so-called "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(12Be) = 39.3 MeV/A. States at 11Be*(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 11Be*(1.78 [Jπ = 5/2+]) implies a ν(0d5/2)2 component in the 12Beg.s..
At E(6Li) = 80 MeV, 11Be*(0.32) is strongly populated and the angular distribution to this state has been measured; 11Be*(2.69, 4.0) are also observed (1977WE03). It is suggested that these states have odd parity (1977WE1B; thesis); however, see (1972AJ01): 9Be(t, p)11Be where positive parity was deduced for 11Be*(2.69).
At E(18O) = 88.7 MeV, 11Be*(0 + 0.32) appear to be involved in the reaction which populates 21Ne(0, 0.35, 1.75, 2.87, 4.43, 6.45) (1974BA15).
Elastic and quasi-elastic scattering angular distributions were measured for 10° ≤ θ ≤ 110° at Ecm = 24.5 MeV 9, 10, 11Be on 550-1000 μg/cm2 targets using a large solid angle ΔE-E Si detector array (2010DI08, 2010SC12). Comparison of the angular distributions reveals a significant reduction of the so-called "Coulomb-nuclear interference peak" for 11Be at θcm ~ 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 σR = 2730 mb is deduced for 11Be, compared with σR = 1090 and 1260 mb for 9, 10Be, respectively; a sizeable 10Be breakup component from 11Be reactions indicates that about 40% of the 11Be total reaction σ is attributed to transfer and/or breakup reactions.
The 11Be*(0, 0.32 MeV) quasi-elastic scattering angular distributions were measured in a large solid angle ΔE-E Si detector array for reactions on a 3.5 mg/cm2 120Sn 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 ΔE-E reaction product identification, while for 52° ≤ θ ≤ 86° the 10Be ejectiles were not distinguishable from the 11Be events. The angular distribution has a "pronounced deviation from the typical Fresnel-type scattering," and the Coulomb-nuclear interference appears strongly damped. Coupled Channels calculations suggest that couplings to the p-states just above the breakup threshold may be important.
Coulomb excitation measurements populating 11Be*(0.32) have been carried out and the resulting B(E1) values are displayed in Table 11.17 (in PDF or PS). These compare with 0.116 ± 0.012 e2 ⋅ fm2 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(11Be) = 40 MeV (2006MA51) and E(11Be) = 40 to 48 MeV (2007MA90). Results are compared with 9Be elastic scattering on 209Bi. Near the Coulomb barrier the 11Be cross sections are larger than the 9Be cross sections, but at higher energies they become more similar, suggesting that direct processes related to the halo structure are more relevant at near-barrier energies.
Fusion cross sections were measured for 209Bi + 11Be at E(11Be) = 30 to 70 MeV (1995YO03, 1996YO08) and E(11Be) = 35 to 50 MeV (1998SI16, 1998SI38). At E(11Be) = 35 to 68 MeV fusion cross sections were measured for 11Be + 238U (1995FE02, 1997FE08, 1999FE12). Also see (1995IM01, 1997SI07, 1997SI25, 1997ZA04, 1999DA02, 1999PE07, 2000HA14, 2000WA37, 2002AL12, 2002DI02, 2002SI07, 2002VI12, 2003BB07, 2003YA17, 2004DI16, 2005LI64).