Precision Measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">B</mml:mi><mml:mi mathvariant="normal">e</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mn>7</mml:mn></mml:mmultiscripts><mml:mo stretchy="false">(</mml:mo><mml:mi>p</mml:mi><mml:mo>,</mml:mo><mml:mi>γ</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:mmultiscripts><mml:mi mathvariant="normal">B</mml:mi><mml:mprescripts/><mml:none/><mml:mn>8</mml:mn></mml:mmultiscripts></mml:math>Cross Section with an Implanted<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">B</mml:mi><mml:mi mathvariant="normal">e</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mn>7</mml:mn></mml:mmultiscripts></mml:math>Target

The $^{7}\mathrm{B}\mathrm{e}(p,\ensuremath{\gamma})^{8}\mathrm{B}$ reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted $^{7}\mathrm{B}\mathrm{e}$ target, a raster-scanned beam, and the elimination of the backscattering loss. The new measurement incorporates a more abundant $^{7}\mathrm{B}\mathrm{e}$ target and a number of improvements in design and procedure. The point at ${E}_{\mathrm{l}\mathrm{a}\mathrm{b}}=991\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$ was measured several times under varying experimental conditions, yielding a value of ${S}_{17}({E}_{\mathrm{c}\mathrm{.}\mathrm{m}\mathrm{.}}=850\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V})=24.0\ifmmode\pm\else\textpm\fi{}0.5\text{ }\text{ }\mathrm{e}\mathrm{V}\text{ }\mathrm{b}$. Measurements were carried out at lower energies as well. Because of the precise knowledge of the implanted $^{7}\mathrm{B}\mathrm{e}$ density profile, it was possible to reconstitute both the off- and on-resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of ${S}_{17}(0)=21.2\ifmmode\pm\else\textpm\fi{}0.7\text{ }\text{ }\mathrm{e}\mathrm{V}\text{ }\mathrm{b}$.

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