A data system for time-of-flight measurements

Abstract

Time interval measurements in a time-of-flight mass spectrometer are digitized by a LeCroy 4208 time-to-digital converter, and fed into a CAMAC processor for analysis and histogramming. In a preliminary version of the system a DEC LSI 11/23 carried out these tasks, but in the present system an INCAA CAPRO 68K handles the higher speed tasks, leaving general housekeeping to the LSI 11/23. The new system has largely overcome the limitations of some earlier systems. Data can now be stored in a 120-Kword × 32-bit histogram in 1 ns bins. Resolution M ΔM ( fwhm) is ∼ 3200 at mass ∼ 720 u for stable ions; it appears to be limited by the axial velocity spread of the ions ejected from the target. Spectra can be accumulated at ∼ 20 000 counts/s. Although the system has been designed for time-of-flight mass spectrometry, it may be useful for other fast timing applications.