A solenoidal electron spectrometer for a precision measurement of the   neutron $\beta$-asymmetry with ultracold neutrons
  We describe an electron spectrometer designed for a precision measurement of the neutron $\beta$-asymmetry with spin-polarized ultracold neutrons. The spectrometer consists of a 1.0-Tesla solenoidal field with two identical multiwire proportional chamber and plastic scintillator electron detector packages situated within 0.6-Tesla field-expansion regions. Select results from performance studies of the spectrometer with calibration sources are reported. 
B. Plaster, R. Carr, B.W. Filippone, D. Harrison, J. Hsiao, T.M. Ito,   J. Liu, J.W. Martin, B. Tipton, J. Yuan