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HK: Physik der Hadronen und Kerne

HK 25: Nuclear and Particle Astrophysics III

HK 25.1: Gruppenbericht

Mittwoch, 13. März 2002, 10:45–11:15, C

Astrophysical S factor for ⁷Be(p,γ)⁸B from precision cross section measurements — •A.R. Junghans¹, E.C. Mohrmann¹, K.A. Snover¹, T.D. Steiger¹, E.G. Adelberger¹, J.M. Casandjian¹, H.E. Swanson¹, L. Buchmann², S.H. Park², and A. Zyuzin² — ¹CENPA, University of Washington, Seattle WA, U.S.A. — ²TRIUMF, Vancouver B.C., Canada

Super-K and SNO are sensitive mainly to neutrinos from the decay of ⁸B produced by the ⁷Be(p,γ)⁸B reaction in the Sun. An improved determination of this cross section (S factor) at solar energies is necessary at the level of ±5% in order that this reaction rate not be the dominant uncertainty in the ν_e flux predicted by solar model calculations¹. We have made new, direct measurements of the ⁷Be(p,γ)⁸B cross section at 27 points from E_cm = 0.18 to 1.2 MeV using the van de Graaff accelerator of the University of Washington with a Terminal Ion Source, and a 106 mCi ⁷Be target produced at TRIUMF and deposited on a Mo backing. The water-cooled target, mounted on the end of a rotating arm, is irradiated in the proton beam and then rotated 180 degrees in front of a Si-detector where the α particles following the β decay of ⁸B are counted. Our technique involves a number of improvements over previous measurements. In our measurements, we have achieved a precision ±5% or better per point. Results will be presented and compared with model calculations and with other experiments. ¹ J. Bahcall et al. Phys. Lett. B433 (1998) 1