A new measurement of 7Be(p,γ) 8B cross section and its astrophysical meaning

Abstract

We measured the 7Be(p,γ) 8B cross section from E p = 221 keV to 1376 keV. A uniformly distributed beam that illuminated the whole area of a small diameter target was used to eliminate systematic error from 7Be target non-uniformity. The energy loss profile of the target to the incident beam was measured using the 7Be(α,γ) 11C resonance at E α = 1376 keV. The (α,γ) measurement also demonstrated that the target had a high 7Be atomic purity. The measured yield of the detected 8B was normalized to the activity of the target and the solid angle of the counting detector. Corrections for 8B decay during bombardment and arm rotation were applied. For the first time, the correction due to lost 8B from backscattering was determined experimentally. A new experiment is presently underway, extending to lower proton energy. Due to a problem in the determination of the α-detector solid angle in the first measurement, the solid angle in the new measurement will be determined by a different technique using a 148Gd α source and a silicon detector whose distance to the source can be precisely adjusted.