Crucial to prediction of the abundances of heavier nuclides in
non-standard BB nucleosynthesis is the 8Li(α,n)11B
reaction . Curiously this reaction has very little eﬀect on the
predicted 11B abundance. Contrarily, most of the abundance
of more massive nuclides, 12C and heavier, are generated at
the time the 8Li abundance is large, so that 8Li(α,n)11B
is crucial for predicting their abundances. Thus it is important that
its cross section be accurately measured.
More recently, the 8Li(α,n)11B reaction has become interesting for another reason, i.e. as one starting point for the r-process . The r-process produces approximately half of the isotopes above mass 80. It is largely believed to take place in the entropy rich bubble of a supernova type IIa between the still hot neutron star and the stalled or slowly moving shock front. In this region, initially all nuclei have been reduced to protons and neutrons, with the neutrons in some excess. During cooling the protons will largely be bound into α particles. The r-process proceeds then largely by neutron capture, starting from the masses reached by the α(αn,γ)9B reaction, the triple α reaction and the 3H(α,γ)7Li(n,γ)8Li(α,n)11B reaction chain. In any case, 8Li(α,n)11B is one way through the mass 8 gap and should be measured regardless of current theoretical thought. This information will have to be known in full extent of time when our theoretical understanding of stellar and cosmological processes are at a higher level than they are today.
Several attempts have been made to determine the low energy cross section for the 8Li(α,n)11B reaction. However, the technique used involved putting the incident 8Li beam into a heavy ion detector ﬁlled with helium and determining the reaction events from the change in trajectory and energy loss of the ions as they moved through the detector. Since there are certainly other processes that can produce trajectory changes, most notably elastic scattering, the analysis of the resulting events have been diﬃcult. The results of those studies suggest that the 8Li(α,n) reactions to excited states of 11B (which decay to the 11B ground state) contribute a large fraction of the total production of 11B from this reaction (so measurements of the cross section for the inverse reaction cannot be used to determine the total cross section of 8Li(α,n)). However, the importance of this cross section to IBBN and r-process models, and the diﬃculty of the previous measurements, make it very desirable to remeasure this cross section at low energies.
In the measurement of 8Li(α,n)11B we propose to detect the recoil 11B for decays from excited states of 11B in coincidence with the γ-decay as well as the ground state decay in single detection. Since the 11B are forwardly focused in the laboratory frame, with a maximum angle of 65◦ at the lowest beam energy, it is possible to cover almost 100% of the angular scattering range. Such high angular coverage would be considerably more difficult for neutron detection as the neutrons are emitted into 4π. Moreover heavy ion detection with gas-filled detectors is significantly more efficient at approximately 100%. The detector named TACTIC (TRIUMF Annular Chamber for Tracking Identification of Charged particles) will be similar, though with many improvements, to the one described in  which was used successfully to measure this reaction at higher energies. In addition, the BGO array from DRAGON will be used for γ detection. We propose to measure the excitation function from the lowest energy attainable, about 0.4 MeV, to 3.0 MeV (in the c.m.). At higher energies the previous 8Li(α,n)11B measurements are considered to be sufficiently accurate. Since the expected resonance structures are of order 100 keV in width, measurements will be performed in 50 keV steps, i.e. at 54 energy settings. The 9Be(α,n)12C reaction has similar properties to the 8Li(α,n)11B but has known cross sections and channels and therefore will be utilized for normalization and calibration purposes. Intensities of 8Li of up to 109 s−1 from tantalum targets have been proven at the ISAC yield station. This will allow for at least 108 s−1 of 8Li at the TUDA position.
 R. Boyd et al., Comments, Nucl. Part. Phys. 22 (1996) 47
 Terasawa et al., APJ, 562 (2001) 470,
T. Kajino, Proceedings of Nuclei in the Cosmos 7 (2002), Nucl Phys. A718 (2003) 295c
 Y. Mizoi et al., Phys. Rev. C62 (2000) 065801
With the advent of high precision measurements of the 7Be(p,γ)8B
cross section , the question of extrapolation to low energies in
reaction has become more pronounced. While this error is not the
nuclear uncertainty anymore in the determination of neutrino properties
solar neutrino observations, a further reduction of this extrapolation
will now and later with other improvements, further restrict these
Indeed, if one takes available theoretical prescriptions for
the scatter in these extrapolations for cross section factor S17(0)
(17 denoting proton and 7Be) is as big as the error from
uncertainties. Possible theoretical extrapolations from the data of
Ref.  are shown in Fig. 1. However, while experimental systematic
be reasonably estimated, the scatter in the extrapolation leads to a
unsatisfactory error estimate because it is quite evident that the
theoretical extrapolations are of
quality and often based upon different experimental input parameters
different model approaches. One profound way to adjust the nuclear part
the theories is a precision measurement of the elastic
cross section of 7Be+p. This 7Be+p elastic
in particular in the s-wave, is a very important ingredient for the
description of the 7Be+p radiative capture. The knowledge
of the elastic scattering cross section is necessary
for the theoretical extrapolation of direct capture measurements to
energies and for the interpretation of Coulombdissociation data. In the
of precise scattering data, phenomenological models like the potential
R-matrix ones generally deduce this information indirectly by assuming
symmetry with the mirror system 7Li+n, for which scattering
are known with high precision.
Recent 7Be+p elastic-scattering experiments have
however raised some
doubts regarding this procedure: (i) the Louvain-la-Neuve experiment
suggests that the 7Be+p scattering length for spin 1 is
the value expected from 7Li+n in the framework of a
model; (ii) the Notre-Dame experiment  is well described by an
formalism which is incompatible with the 7Li+n scattering
length for spin
2 [7,8]. A possible explanation for such a charge dependence could be
existence of wide s-wave states at an excitation energy of about 3.5
in both the 8Li and 8B nuclei, corresponding to
the 8Be excited states seen
in 7Li+p elastic scattering . For 7Be+p,
these states would be much above
threshold (0.1375 MeV excitation w.r.t. 8B g.s.) and would
only have a weak influence on
lengths. For 7Li+n, they would be much closer to threshold
(2.0328 MeV excitation w.r.t. 8Li g.s.) and
could strongly affect scattering lengths, which would cause an apparent
of charge symmetry.
Both 7Be+p scattering experiments quoted above [5,6] are
makes theoretical discussions very ambiguous. In fact, the s-wave
length error (∼40%) derived at LLN leads to an uncertainty of about 5%
the theoretical extrapolation. More precise 7Be+p
scattering data would
to test the reliability of the charge-symmetry hypothesis, to check the
of wide s-wave states in 8B, or even to eliminate the input
the 7Be+p capture calculations. Various theoretical models(potential
R-matrix, microscopic cluster model) can also be tested on these data
fitted to them, which will tighten the constrain on the 7Be+p
section. With the TACTIC detector we will strive for a 10% error in
scattering length. The TACTIC detector will also allow
for the first time a measurement of the inelastic proton channel to the
state of 7Be (429 keV). There is also the possibility to
exploit the multi-tracking capabilities of TACTIC by measuring, also
for the first time, the 3He
channel opening, 7Be+p→3He+4He+p, at Ecm
energies above 1.588 MeV.
 A. Junghans et al., Phys. Rev. C68
 C. Angulo et al., Nucl. Phys. A716 (2003) 211
 Rogachev et al., Phys. Rev. C64 (2001) 061601
 Barker and Mukhamezhanov, Nucl. Phys. A673 (2000) 526
 JM. Sparenberg, to be published and private communication (2004)
 Brown et al., Nucl. Phys. A206 (1973) 353
Measured abundance for 7Li is within a factor of two agreement with Standard BBN models, however for the more fragile 6Li its abundance has been observed at a level three orders of magnitude above those predicted by standard Big Bang Nucleosynthesis model predictions. These discrepancies are known as the Lithium Anomaly.
The standard BBN model predicts [7Li / 6Li] on the order of a 30,000 or greater. Precise measurements of isotopic ratio indicate that [7Li / 6Li] ~ 12.5+/- 2.8. This factor of 2,500 discrepancy between the standard BBN model predictions and measurement we shall call the Strong Lithium Anomaly.
This experiment will study a simple hypothesis to find a possible explanation for the Strong Lithium Anomaly, through the study of the transfer reaction 7Li(3He, 4He)6Li reaction. The 7Li(3He, 4He) 6Li reaction will build up the 6Li abundance, which deals with the Strong Lithium Anomaly, whilst serving to deplete the 7Li abundance, which relates to the Weak Lithium Anomaly.
It is proposed that an additional study be undertaken of the 7Li(3H, 4He) 6He reaction either at TRIUMF or at another facility. The halo nuclei 6He is a mirror nuclei to 6Li and decays to 6Li.
Under this proposal measurements of the 7Li(3He, 4He) 6Li cross section at low centre of mass energy are to be undertaken at TRIUMF using the TACTIC detector .