A GAS-INJECTION NEGATIVE ION SOURCE FOR ACCELERATOR MASS SPECTROMETRY

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2004-11-04

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Accelerator mass spectrometry is an ultra-sensitive isotopic analysis technique that allows for the determination of rare long-lived radionuclides such as radiocarbon. Historically, the technique has required that samples be processed into graphite prior to analysis. The processing is time and labor intensive and limits the technique due to contamination. There has been recent interest to develop an ion source that would allow direct injection of gaseous samples, thus eliminating the processing. Previous attempts to build such an ion source have been limited by low mass usage efficiency and severe memory effects. This dissertation describes the development of a plasma negative ion source that allows direct injection of gaseous material. This ion source was able to produce a negative carbon ion beam of approximately 4.5 uA from carbon dioxide. This beam intensity is lower than both of the competing designs. However, this ion source was able to operate with a mass efficiency of nearly 0.15% which exceeds one of the competing designs. It was also free from significant memory effects which plagued the other competing design. There are many improvements to the design of this ion source that would further enhance its performance. These results are promising and show that this type of ion source could be used effectively in an accelerator mass spectrometry system.

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