(See 11.1 (in PDF or PS) and Energy Level Diagram for 11Li and Isobar Diagram )
Q = -33.3 ± 0.5 mb (2008NE11); sign is from theory.
We accept the most precise measurement of the 11Li mass M = 11.04372361 ± 0.00000069 u which yields a mass excess of 40728.28 ± 0.64 keV (2008SM03: TITAN). This values differs from Audi et al. (2003AU03) by 70 keV and results in the value S2n = 369.15 ± 0.65 keV. Other precise mass measurements have indicated ΔM = 40719 ± 5 keV (S2n = 378 ± 5 keV) (2005BB01, 2008BA18, 2009GA24: MINSTRAL). Values derived from reaction Q-values, in terms of the 2-neutron separation energy, are S2n = 363 ± 22 keV (2009RO04), 295 ± 35 keV (1993YO07), 340 ± 50 keV (1991KO1U), 320 ± 120 keV (1988WO09) and 170 ± 80 keV (1975TH08).
The nuclear charge radius derived using ΔM = 40728.28 ± 0.64 keV is reported as, for example, Rrmscharge = 2.427 ± 0.016 (measurement) ± 0.030 (reference) fm (2008SM03) and Rrmscharge = 2.48 ± 0.04 (2011NO11); also see (2006PU03, 2006SA52, 2010PU01).
Published values of the 11Li half-life are 8.99 ± 0.10 ms (1997MO35), 8.2 ± 0.2 ms (1996MU19), 8.5 ± 0.2 ms (1974RO31) [8.8 ± 1.2 ms and 9.0 ± 0.8 ms are also independently measured in (1974RO31)], 8.83 ± 0.12 ms (1981BJ01), 7.7 ± 0.6 ms (1986CU01) and 8.5 ± 1.0 ms (1969KL08). An unpublished value of 8.4 ± 0.2 ms (1995RE1M) is referenced in (2003AU03). The weighted average of all measurements is 8.75 ± 0.07 ms; however, this value has poor overlap with measurements and indicates that uncertainties are significantly underestimated in some cases. We accept the (2003AU03) value, 8.75 ± 0.14 ms, which is obtained by enlarging the uncertainty of the weighted average.
The β-decay is complex and details reported for branching ratios are ambiguous. Most of the decay populates low-lying states in 11Be (> 94%); all but 11Be*(0, 0.32) are unstable with respect to neutron emission. At higher excitation energies the 11Be states are also open to deuteron, triton, α and 6He emission. Measurements of γ-rays following 11Li β-decay have provided new information on 10Be and 11Be states; see 11Be reaction 15 and (1996MU19, 1997AO01, 1997AO04, 1997BO01, 1997BO03, 1997MO35, 1997MU06, 2003FY01, 2004FY01, 2004HI24, 2004SA46, 2005HI03, 2008MA34, 2009MA54).
The β-delayed particle emission branching ratios appear to show discrepancies. Details are given in 11.14 (in PDF or PS). A summary suggests: β-1n = 86.3 ± 0.9 %, β-2n = 4.1 ± 0.4 %, β-3n = 1.9 ± 0.2 % and Pn = 100.3 ± 1.4 % using P11Be*(0.32) = 7.7 ± 0.8 % (2005HI03). A precise determination of the β-d branch for low-energy deuterons is complicated by contamination from β-delayed alpha particles though published values indicate β-d = (1.30 ± 0.13) × 10-2 % (2008RA23); β-t = (0.93 ± 0.08) × 10-2 % (2009MA72); β-α = 1.7 ± 0.3 %. A theoretical analysis suggests β-(p + n) ≈ 10-10 which is roughly six orders of magnitude smaller than the β-d ratio (2010BA44).
Studies of β-decay to 11Be states near Ex = 18.5 MeV (1996MU19, 1997BO03, 1997MU06, 2008MA34) have searched for β-delayed deuterons, which may indicate a deuteron-halo state in 11Be that is analogous to the 2-neutron halo ground state of 11Li; also see (1995OH02, 1995ZH31, 2004KU27, 2006BA73, 2011TU07). The β-decay shows retardation because of poor overlap of the initial and final wavefunctions (1995OT01). The s-wave and p-wave components in the 2-neutron valence wavefunctions are discussed in, for example, (1994SU12, 1996SU23, 1997BO01, 1997SU12, 2002SU16). See also (1997RI04, 2003SU04).
A β-NMR technique was used to measure the quadrupole moment of 11Li (1992AR07). The measured quantity |Q(11Li)/Q(9Li)| = 1.088 ± 0.015 implies Q(11Li) = -33.3 ± 0.5 mb (2008NE11): negative sign assumed from theory. Also see Q(11Li) = -31.2 ± 4.5 mb (1992AR07) and (1993NE08, 1994AR19).
Scattering of 11Li ions from 1H has been measured at energies from 62 to 700 MeV/A (see 11.2 (in PDF or PS)). The elastic scattering distributions have been analyzed to evaluate possible signatures of the 2-neutron halo and to determine the nuclear size; Rrmsmatter = 3.62 ± 0.19 fm (2002EG02) and 3.71 ± 0.20 fm (2006AL16, 2006DO02). At E(11Li) = 75 MeV/A states are reported at 0, 1.25 ± 0.15, 3.0 ± 0.2, (4.90 ± 0.25), (6.40 ± 0.25), and 11.3 ± 0.35 MeV (1996KO02, 1997KO06). Evidence for an L = 1 state with Ex = 1.3 MeV (Γ = 0.75 ± 0.60 MeV) is analyzed in (1992FAZV, 1997KA19, 1997KA42, 1997KO11, 1998KA33, 1999KA68, 2001CR06, 2002CR06, 2004ER07); the state is attributed to either the soft-dipole resonance or 2-neutron removal threshold effects. See (1993HI04, 1994CH07, 1996CR06) for comments on the influence of the 9Li core. Also see (1991AL13, 1993AL06, 1993BE05, 1993KO44, 1993SU04, 1995SA33, 1996CR06, 1997CO11, 1997KN07, 1997KO12, 1998AN25, 1998DO16, 1999AL13, 1999CR02, 1999GR34, 2000GU19, 2000KA04, 2001CR02, 2001KI29, 2002CR02, 2002GU02, 2004AL09, 2004ER05, 2005KA21, 2005KI22, 2009HA04) and reaction 12C(11Li, 11Li).
Two techniques were used to determine the 1H(11Li, 9Li)3H reaction Q-value (2009RO04). First, a complete kinematic reconstruction of the ejectiles yielded Q = 8.123 ± 0.025 MeV. Second, two-body reaction recoil energy kinematics of ejectiles at 180° yielded Q = 8.106 ± 0.042 MeV. The weighted average is Q = 8.119 ± 0.022 MeV, which corresponds to S2n = 363 ± 22 keV.
At E(11Li) = 3 MeV/A the two halo neutron transfer reaction is studied by measuring the angular distribution of 9Li*(0, 2.69) (2008TA13); n-n correlations and the reaction mechanism are discussed. The population of 9Li*(2.69: Jπ = 1/2-) suggests a 1+ or 2+ configuration of the halo neutrons. Also see analysis of a proposed phonon mediated pairing interaction given in (2010PO08).
At E(14C) = 334.4 MeV states corresponding to 11Li*(0, 2.48 ± 0.07, 4.86 ± 0.07, 6.22 ± 0.08) were observed with Γ = 1.2 ± 0.2, < 0.1 and < 0.1 MeV for the excited states, respectively (1995BO15, 1995VO05).
The radius of 11Li determined from pion double charge-exchange reactions on 11B at Tπ = 164 MeV is Rrmsneutrons = 3.28+0.24-0.33 fm, and the radius of the valence neutrons is Rrmsvalence = 5.1+0.6-0.9 fm (1991GI06). See also (1992ES02, 1994LE06, 1995HA31). For reaction (b) see (1997YA11).
At E(11Li) = 246 MeV/A, analysis of a complete three-body kinematical measurement of 11Li breakup on a 12C target indicates the reaction mechanism is 11Li inelastic scattering to unbound states at Ex = 1.31 ± 0.05 and 2.52 ± 0.27 MeV with Γ = 0.26 ± 0.24 and 2.91 ± 0.72 MeV, respectively (2007SI24). Note: these excitation energies are adjusted upward by 70 keV to account for the change in the accepted 11Li mass and 2n separation energy.
Elastic and quasi-elastic scattering of 11Li ions on 12C and 28Si have been reported at energies from 30 to 60 MeV. Optical model analysis of the angular distributions yield parameters that are significantly different from standard parameters (reaction (a): 1992KO14, 2003PE01) and (reaction (b): 1993LE14). The effects of refraction and absorption are analyzed in (1991SA02, 1992AL05, 1993ME02, 1995DA05, 1995EV03, 1996EV01, 1997MO42, 2000MO34).
See also (1991CA14, 1991TA21, 1992TA16, 1992VE03, 1993DA09, 1993SU04, 1993TH01, 1994AL02, 1994CA07, 1994HU04, 1994SA16, 1994SK04, 1995AL01, 1995AL02, 1995AN06, 1995CO01, 1995FA17, 1995FO08, 1995GA24, 1995HU08, 1995KH11, 1996CA01, 1996KN02, 1996RA18, 1996UE01, 1997CH32, 1997KN07, 1997MO24, 1998CH18, 1998MO27, 2000BO45, 2000PA14, 2006DL01, 2011IB02) and reaction 2.
The kinematic reconstruction of p + d pairs resulting from the capture of stopped π- on 14C indicates population of 11Li*(1.09 ± 0.07, 2.14 ± 0.12, 3.70 ± 0.13) (1998GO24) and 11Li*(0.92 ± 0.15, 2.29 ± 0.25, 3.90 ± 0.25) with Γ ≈ 0.3, ≈ 0.7 and < 0.2 MeV, respectively (2010GU04). There was no evidence for breakup into 9Lig.s.+ di-neutron; however in the high-excitation energy part of the spectrum the two neutron pairs corresponding to breakups via 9Li*(2.69, 4.31) were strongly correlated. Note: these excitation energies are adjusted upward by 70 keV to account for the change in the accepted 11Li mass and 2n separation energy.
At E(11B) = 32 MeV the ground state of 11Li was observed, and the Q-value for the reaction was measured as Q = -37.120 ± 0.035 MeV (1993YO07, 1995BE30). This corresponds to S2n = 295 ± 35 keV. See also (1992PEZT, 1993BEZO).
At E(14C) = 335.9 MeV states corresponding to 11Li*(0, (1.2), 2.45 ± 0.10, 4.84 ± 0.10, 6.22 ± 0.10) were populated with Γ = 1.2 ± 0.3, < 0.1 and < 0.1 MeV for the states above 2 MeV, respectively (1995BO15, 1995VO05). These states were tentatively interpreted as excitations of the 9Li core (1995VO05).
Studies of 11Li have been carried out via measurement of interaction cross sections and breakup reaction cross sections, see 11.3 (in PDF or PS). The anomalously large cross sections observed in the studies can be related to the extent of the valence neutrons by various reaction models (1990HA15, 1990LI39, 1991MU19, 1992TA15, 1994BEZX, 1996AL13, 1996WA27, 2000EV03, 2001EG02, 2001OZ04). Also see (1990BE29, 1992OG02, 1992SA11, 1992SO15, 1992YA02, 1993BA71, 1993MA25, 1995PE19, 1996AL24, 1996BU09, 1997ES07, 1997FO04, 1997TO04, 1997ZA08, 1998BE09, 1998KN03, 1999KA67, 1999KN04, 2000GA20, 2000GA31, 2001BH02, 2003KH10, 2004CA18, 2004LO12). Measurements of the parallel and transverse momentum distributions of outgoing fragments can 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 (1990UT01, 1992TA15, 1992ZH05, 1993BE45, 1993KO11, 1993LEZR, 1994JO04, 1995HA17, 1995OR02, 1995ZH13, 1995ZI03, 1996GA09, 1997GA04, 1997GA10, 1997OR03, 1997ZI04, 2001AX01, 2007SI24). Also see (1991ZH11, 1992BE43, 1992SH09, 1993ES02, 1993RO16, 1995BA32, 1995ES01, 1995OG04, 1996BA68, 2000BA47, 2001GA09, 2004BE45, 2009SH25). The measurements appear consistent with an Rrmsmatter size that is greater than 3 fm and a valence neutron "halo" that extends to Rrmsvalence = 5 fm or more. Comments on the interference effects between nuclear and Coulomb breakup components are given in (1990BE29, 1993BA71, 1993EV02, 1993IV01, 1996DA03, 2000GA31).
The complete kinematical detection of 9Li + 2n following Coulomb breakup on high-Z targets permits a determination of the dipole strength distribution in the region just above the neutron binding threshold. At E(11Li) = 280 MeV/A (1997ZI04) the excitation strength function was decomposed into two Gaussian components; analysis indicates peaks at Ex = 1.1 ± 0.1 and 2.5 ± 0.2 MeV with Γ = 0.7 ± 0.2 and 2.1 ± 0.6 MeV, respectively. Note: these excitation energies are adjusted upward by 70 keV to account for the change in the accepted 11Li mass and 2n separation energy. The two peaks, which were assumed to have E1 character, carried 1.2 ± 0.3 % and 7 ± 2 % of the energy weighted sum rule. At E(11Li) = 30 MeV/A (1996GA08, 1996IE01) report that the dipole strength function is consistent with a resonance at Eres = 0.7 MeV, Γ = 0.8 MeV, but considering Coulomb re-acceleration of the charged particles in the Z-field of the target indicates a negligible lifetime for any resonant state and presents a contradiction to any soft-dipole resonant state behavior (2001GA22). A measurement of the relative three-body breakup energy at E(11Li) ≈ 70 MeV/A (2005NA40, 2006NA21, 2006NA39, 2007NA22) showed significant strength at low energies, peaking at Erel ≈ 0.3 MeV. This corresponds to Ex ≈ 0.6 MeV with Γ ≈ 0.6 MeV; the corresponding strength for 0 ≤ Ex ≤ 3 MeV is B(E1) = 1.42 ± 0.18 e2 ⋅ fm2. Also see (1990BE04, 1990BE07, 1990HA33, 1990HO26, 1990SA41, 1990SU16, 1991FA09, 1991HO06, 1991HU03, 1991TE01, 1992BA63, 1992BE40, 1992CA20, 1992ES01, 1992SA10, 1992SU06, 1993BE05, 1993CA34, 1993GO17, 1993ZHZV, 1994TY02, 1995FU12, 1995RO13, 1996CA12, 1997BO08, 1998CO11, 1998CO22, 1999GA08, 1999KA68, 2000FO09, 2001FI14, 2001SA79, 2003MY03, 2003MY04, 2004ER05, 2004ER07, 2004MY01, 2006AO02, 2007BE58, 2007ES04, 2007MY04, 2007SA41, 2009HA30).
A simple interpretation of 11Li describes the system as a 9Li core with the two valence neutrons bound in a simple potential (1987HA30). In a search for possible evidence of a di-neutron, the data have been evaluated with an emphasis on measurements of the correlation of the valence neutrons after breakup (1992BE40, 1995IS04, 1995SH14, 1996CH38, 1996GA08, 1996IE01, 1997KU07, 1997LU08, 1997ZI04, 1998GA37, 2000EV03, 2000EV04, 2000MA12, 2001DA17, 2004PE01, 2004PE08, 2004WE05, 2009HA37, 2010HA10). Further studies emphasize the determination of s-wave to p-wave contributions for the valence neutron wavefunctions and implications for 10Li (1992ZH05, 1995ZI03, 1996GA09, 1997GA04, 1999SI08, 2003MY03, 2004MY01). Overviews of the experimental work can be found in (1993KO11, 1994JO04, 1997OR03, 2001EG02, 2001OZ04, 2002BR01, 2002WA08). In all cases the emitted neutron pairs show no strong correlations, arguing against the existence of a di-neutron in 11Li.