A new double focusing beta spectrometer and the empirical optimization of its performance

The design, construction and performance of a double focusing electron spectrometer are described. The spectrometer has a mean radius of 30 cm, and a maximum transmission of 5% of 4π, at a resolution of 1.5%. Resolutions of 0.07% have been obtained at a transmission of 0.5% of 4π with a source 0.020 inches wide. Three separate criteria of optimum performance have been studied experimentally; the elimination of aberrations associated with φ z the elimination of aberrations associated with φ r , and an intermediate focusing in which the φ z and φ r aberrations are equal and overlap. The performance of this spectrometer under the first of these three criteria is described in detail.