Neutron time of flight spectrometer for velocity selector calibration

Neutron wavelength λ and wavelength resolution Δλ/λ (FWHM) can be measured by time of flight spectrometer. Spectrometer structure and parameters of its key component chopper are introduced. ³He proportional counter and two dimension position sensitive detector are used in detection system. Multi-channel scaler is chosen as data acquisition system and electronic circuitry of detection system is designed. The impact of count loss rate on wavelength resolution measurement is analyzed. In order to ensure the wavelength resolution measurement error be less than 0.9%, the upper limits of Gauss peak count rate for two detectors are acquired. According to upper limits of Gauss peak count rate, upper limit of neutron fluence rate for neutron beam going to chopper and upper limit of mean count rate during the whole time is acquired for each detector. Floor limit of total measuring time is calculated using upper limits of mean count rate. (authors)