Neural-a detector for neutron reactions

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The long-lived, radioisotope, ^26Al, was discovered in the cosmos 30 years ago and its galactic distribution follows one of population I stars, i.e. massive, short-lived stars. Such stars typically end up in core collapse supernovae. The main production of ^26Al happens in the explosive neon burning following the core collapse of the massive star. In this scenario ^26Al is produced by capture of secondary protons or the (p,n) reaction. Since free neutrons are also present, this leads to the main destructive reactions, namely ^26Al(n,p) ^26Mg and ^26Al(n,alpha) ^23Na, which dominate the rate. The most critical neutron energy range for this destruction is from 150-200 keV and unfortunately, no measurements exist. We plan to use the unique capability of TRIUMF-ISAC in producing an intense radioactive ^26Al beam to fabricate an implanted ^26Al target in a thin carbon foil. Such a target has the unique property that (i), there are no major cross contaminations present in the target and (ii) a better kinematic reconstruction combined with an improved background suppression is feasible. Indeed, previous measurements were prevented largely by background problems to cover the neutron energy range. Besides this novel target approach, we also plan to develop a new kind of detector. This detector (dubbed Neural) will consist of a time projection chamber along with silicon detectors surrounding the time projection chamber. Besides obtaining stopping power information, it will also be possible to detect the recoil ^23Na and ^26Mg particles. This will put further constrains on the background and, in principle, even allow a determination of the neutron energy. The neutron energy at the LANSCE facility in Los Alamos is typically given by time of flight conditions and shows some spread for a given time. The proposed experimental approach has achieved high marks with the Lansce PAC. In December of 2009 a run at Los Alamos is scheduled to test this detector. To do this, we are assembling a detector consisting of parts obtained from other experimental facilities at TRIUMF-ISAC. However, the detector does not cover the maximum solid angle due to lack of silicon. Therefore, we request funding to construct a new, improved detection system.