Measurement of the ⁸B neutrino spectrum

The neutrino spectrum from the decay of ⁸B is a crucial ingredient in interpreting recent data from solar neutrino detectors. The β⁺ decay of ⁸B proceeds to a broad state in ⁸Be, and the shape of the neutrino spectrum may be obtained from a measurement of the α spectrum following the β⁺ decay. A new technique has been used at the ATLAS accelerator to measure this spectrum by implanting ⁸B particles into the mid-plane of a 91 μm thick Si detector. The advantage of this method is that both α particles are detected and systematic effects due to energy loss in catcher foils and dead layers of the detector are eliminated. To calibrate the detector, α's from the decay of ²⁰Na ions produced and implanted with the same technique were used.