Metallic beryllium-7 target of small diameter

The stellar Be-7(p, gamma)B-8 reaction rate has the largest uncertainty amo ng all nuclear reaction rates in the standard solar model. However, the sol ar neutrino flux predicted for the majority of proposed and existing solar neutrino detectors is directly dependent on the rate of Be-7(p, gamma)B-8 r eaction. The existing solar neutrino detectors measure rate of B-8 decay ne utrinos that is too low. This constitutes largely the solar neutrino proble m. Existing measurements of the Be-7(p, gamma)B-8 reaction rate disagree wi th one another, indicating the need for more precise experiments. To provid e the required targets a new procedure for Be-7 production, separation and target manufacturing has been developed. First, a lithium target has been d esigned for Be-7 production at TRIUMF's 13 MeV cyclotron. The lithium targe t has been extensively tested at 50 mu A proton beam current yielding 8.1 M Bq/mu A h of Be-7. An adsorption filtration technique has been developed f or 7Be separation. Up to 99% of Be-7 can be recovered from an irradiated li thium target. Reduction evaporation of beryllium oxide and vacuum re-distil lation of beryllium have been used to deposit a thin film of metal Be-7 on the surface of molybdenum target backing. The chemical composition of some beryllium targets has been determined. The total level of impurities was co nsistently at 30-40% by proton beam stopping power. It is intended to produ ce a number of metallic Be-7 targets with concentration of Be-7 of 10(16)-1 0(17) atoms in an area of approximately 3 mm(2). (C) 1999 Elsevier Science B.V. All rights reserved.