Towards an intense radioactive 8Li beam at SARAF Phase I

Abstract

The 8Li(α,n)11B reaction plays an important role in the r-process nucleosynthesis occurring in type II supernovae and in binary neutron stars. At high rates, this reaction can lead, despite the short 8Li half-life, to production of seed nuclei through a chain of reactions, which can then cause the formation of heavier nuclei via (n,γ) reactions. Several measurements of this reaction were carried out in the last few years using fast 8Li beams that are available at several RIB facilities at limited currents. A new production method for light Radioactive Ion Beams (RIB) via fast neutron reactions is conceptually able to provide orders of magnitude higher RIB currents, up to 1012 pps. The high efficiency of the two-target production method has been experimentally proven for 6He production, in a similar manner to the 8Li production. We present a unique apparatus for 8Li production and extraction at the Soreq Applied Research Accelerator Facility - SARAF. In 2011, it is expected that SARAF Phase-I will produce high intensity, 5 MeV deuteron beams for limited experiments. By using a LiF neutron converter, neutrons with energies of up to 20 MeV and a total yield of 1012 fast n/sec will be available per 1 mA of deuterons. As a secondary production target we are using discs of 65% porous B4C, mounted inside a high temperature furnace. 8Li, produced via the 11B(n,α)8Li reaction channel, diffuses out of the B4C target and is ionized in a thin rhenium surface ionizer. The total efficiency of 8Li RIB creation will be measured by means of alpha and beta measurements. Following the experiment at SARAF Phase I, better production and extraction schemes of light RIB, of great interest in various nuclear and astrophysics-related measurements, may become possible.