CHELSI: Recent developments in the design and performance of a high-energy neutron spectrometer

As a precursor to the development of a portable instrument, data has been obtained using a 1″×1″ CsI-based probe and a digital spectrometer. This system has been used to collect data on the 90 m flight path at the LANSCE/WNR facility at an average neutron energy of 335 MeV. The spectrometer has the capability, in addition to storing individual waveforms for later analysis, of recording time-of-flight data and calculating a pulse shape parameter and pulse height for each scintillation event in real time. Combining these data with traditional multichannel analyzer data has yielded a set of empirical response functions with respect to neutron energy. Analysis of the charged particle spectra has yielded an overall average count rate of 0.12±0.02 cps/μSv h for a 1″×1″ CsI(Tl) scintillator in this neutron field.