A solenoidal electron spectrometer for a precision measurement of the neutron ββ-asymmetry with ultracold neutrons

We describe an electron spectrometer designed for a precision measurement of the neutron ββ-asymmetry with spin-polarized ultracold neutrons. The spectrometer consists of a 1.0-T solenoidal field with two identical multiwire proportional chamber and plastic scintillator electron detector packages situated within 0.6-T field-expansion regions. Select results from performance studies of the spectrometer with calibration sources are reported.