We have constructed a mass spectrometer system for noble gas isotopes. This system consists of a noble gas extraction and purification system for an extremely small amount of extraterrestrial sample and a conventional (30 cm radius, 90° magnetic sector) single focus mass spectrometer, which are made of stainless steel.
The sample is heated in a small tungsten basket. Extracted noble gases are purified by hot Ti-Zr getters and a getter pump.
The mass spectrometer is controlled by a personal computer to obtain high precision. The computer is connected with a programmable voltage current source and digital multimeters through GP-IB interface. The computer controls these instruments and the isotope data are recorded on a floppy disk. The software was developed with N88-basic (86).
In order to improve the system sensitivity, ion counting method was introduced. The number of ions is counted with a multichannel scaler by means of a constant fraction circuit.