UBC Theses and Dissertations

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UBC Theses and Dissertations

The development of a completely automated oxygen isotope mass spectrometer Ahern, Timothy Keith


A completely automated mass spectrometer system has been developed to measure the oxygen isotope ratio of carbon dioxide samples. The system has been shown to have a precision of 0.03°/oo, which is comparable to that quoted for any other system in the world. In addition, the facility is capable of analyzing over one hundred samples per day. The system uses an Interdata minicomputer as the primary controller. The minicomputer monitors the quality of analyses, on-line, and thereby insures that all DEL values are measured to at least 0.04°/oo. Host of the sophistication resides in intelligent controllers within the mass spectrometer console. This design gives a technician considerable power when operating the system in a manual mode. The intelligence of the system is contained within hardware circuits, software within the minicomputer and firmware written for a Motorola 6802 microprocessor. A major contribution of this thesis has been the design and installation of an automated mass spectrometer inlet system. A microprocessor based inlet system controller maximizes the throughput of carbon dioxide samples within the inlet system. The inlet system normally contains four different aliquots of carbon dioxide and introduces these samples to the mass spectrometer, in proper sequence, through a single mass spectrometer admittance leak. The system has been used in the analysis of 111 samples of ice taken from the Steele Glacier, Yukon Territory. The samples taken from a vertical borehole, displayed a sawtooth variation of the oxygen isotope ratio with depth. The data have been explained by a physical model described in an appendix to this thesis. If our interpretation is correct, the isotopic variations have recorded at least four surges of the Steele Glacier.

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