Metallic beryllium-7 target of small diameter

The stellar 7Be(p, γ)8B reaction rate has the largest uncertainty among all nuclear reaction rates in the standard solar model. However, the solar neutrino flux predicted for the majority of proposed and existing solar neutrino detectors is directly dependent on the rate of 7Be(p, γ)8B reaction. The existing solar neutrino detectors measure rate of 8B decay neutrinos that is too low. This constitutes largely the solar neutrino problem. Existing measurements of the 7Be(p, γ)8B reaction rate disagree with one another, indicating the need for more precise experiments. To provide the required targets a new procedure for 7Be production, separation and target manufacturing has been developed. First, a lithium target has been designed for 7Be production at TRIUMFʹs 13 MeV cyclotron. The lithium target has been extensively tested at 50 μA proton beam current yielding 8.1 MBq/μA h of 7Be. An adsorption filtration technique has been developed for 7Be separation. Up to 99% of 7Be can be recovered from an irradiated lithium target. Reduction evaporation of beryllium oxide and vacuum re-distillation of beryllium have been used to deposit a thin film of metal 7Be on the surface of molybdenum target backing. The chemical composition of some beryllium targets has been determined. The total level of impurities was consistently at 30–40% by proton beam stopping power. It is intended to produce a number of metallic 7Be targets with concentration of 7Be of 1016–1017 atoms in an area of approximately 3 mm2.