Detector and slit configuration in an isotope ratio mass spectrometer

A method of configuring a Faraday detector in a mass spectrometer is described. The mass spectrometer defines a central ion beam axis, and the Faraday detector is moveable relative to the central ion beam axis. The Faraday detector includes a detector arrangement having a detector surface, and a Faraday slit defining an entrance for ions into the detector arrangement. The Faraday detector has an axis of elongation which extends through the Faraday slit. A width of the Faraday slit is chosen, and the angle between the axis of elongation of the Faraday detector and the central ion beam axis is adjusted such that ions striking the detector surface do not generate secondary electrons.