Isotopic analysis of iodine using negative surface ionization

Negative surface ionization (NSI) of iodine has been studied on a series of low work function surfaces with the intent of developing improved methods for isotopic analysis, particularly at the environmental level (127/129 = 104-108). The most promising method gives 1% ionization/transmission efficiency without measurable tailing from the major peak at ratios of 108 and without spectral interferences. These results demonstrate the feasibility of performing environmental measurements by this method, and support the hypothesis that very large isotope ratios (> 106) are more easily measured with negative than with positive ions. (orig.)