The 11B(p→,γ)12C reaction below 100 keV

The ¹¹B(p^→,γ)¹²C reaction was studied by measuring the γ rays that were produced when 80-100-keV polarized protons were stopped in a thick ¹¹B target. Cross sections and vector analyzing powers at 90° were determined as a function of energy for capture to the ground and first excited states of ¹²C. These analyzing powers are particularly sensitive to the interference between s-and p-wave contributions, and to the relative phase between direct and resonance amplitudes. The results were used to produce a reliable extrapolation of the astrophysical S factor at 0 keV by means of a direct-capture-plus-resonances model calculation. The value of S(0) that was obtained for ¹¹B(p,γ0), 1.8±0.4 keV b, is in agreement with previously determined values, but for ¹¹B(p,γ1) the value of S(0) is 3.5±0.6 keVb and is more than twice as large as previously determined values.

Duke Scholars

Author John H Kelley Physics