Measurement of the 7Be(p,γ)8B reaction with solid state targets

Complete text of publication follows. The absolute cross section σ17(E) of the 7Be(p,γ)8B reaction influences sensitively the calculated flux of high-energy neutrinos from the sun. Due to its importance for the solar-neutrino-puzzle, the cross section σ17(E) should be known with adequate precision, i.e. to better than 5%. In order to reach this goal a new measurement of σ17(E) was performed at the Dynamitron Tandem Laboratorium in Bochum. This experiment includes for the first time measurements with Pt and Cu backings taking into consideration the possible influence of the recoil loss effect. The 7Be nuclides were produced in a metallic Li sample via the 7Li(p,n)7Be reaction using a 11.4 MeV proton beam (20μA) from the cyclotron of the ATOMKI. Using hot chemistry the activated samples were transformed into nearly pure 7Be. The 4 MV Dynamitron tandem accelerator at the Ruhr-Universitaet Bochum provided a proton beam at Ep = 0.3 to 3 MeV with a maximum current in the range of 10 μA. The cross section was determined from the yield of the 8B recoils, which was deduced from the β-delayed α-decay of 8B (T1/2 = 770 ms). The target was mounted on a rotating wheel, which moved the target between the beam irradiation position and the 8B-decay counting position (Si detector). The detector efficiency, the irradiation/counting-, and the transfer time-intervals were determined using a calibrated α-source mounted in the target position. The beam current was measured in a Faraday cup mounted behind the target. The number of 7Be target nuclei was determined by measuring the γ-activity of the target. The measurements were carried out for targets both on Pt and Cu backing. Preliminary results are in good agreement with the measurement of Filippone et al. and suggest that within the experimental errors there is no influence of the recoil loss effect. (author)