Speaker
Description
The available data on $^{12}$Be are ambiguous and limited despite numerous attempts via direct and indirect reactions. For the three previous (d,p) reactions[1-3], their reaction energies and angular coverage were not optimized so the data could not be easily interpreted in terms of well-tested reaction mechanisms. For another, these measurements provided limited information on the unbound excited states and did not achieve good enough Q-value resolution to isolate the $0^+_2$ and 2$^+_1$ states which are just 150 keV part. To resolve this situation, a new $^{11}$Be$(d,p)$ measurement has been carried out using ISS at ISOLDE at an energy of 9.78 MeV/u. The $0^+_2$ and $2^+_1$ states have been isolated owing to the good resolution of ISS. The neutron $1s_{1/2}$ spectroscopic factor of the $0^+_2$ level has been determined, which will allow for its matter radius extraction, and hence, if it has a two-neutron halo structure, similar to the $^{11}$Li ground state. The recently observed $0^-$ state [4] has been confirmed and its width and excitation energy have been precisely determined, located just 40 keV above Sn. The spectroscopic factors of states below 5 MeV have also been determined and suggestions of the spin-parities of the unbound states will been made. In particular, a new resonance at ~4.2 MeV has been observed for the first time in $^{12}$Be. The new results will be compared with shell model calculations incorporating effective interactions, Gamow shell model (GSM) calculations [5] and Gamow coupled-channel method (GCC) calculations [6] incorporating the continuum coupling effects.
