Advanced instrumentation for accelerator mass spectrometry

加速器质谱法（AMS）的优点主要局限于容易产生负离子和具有不产生负离子的等压线的元素，如碳-14和碘-129。在加速器质谱法中，同位素和稀有原子可以在亚毫克的样品中测量，灵敏度接近十亿分之一。对于不满足其中一个或两个条件的元素，分析策略的发展受到限制，通常仅限于使用较大的加速器（bbb50 MV）。IsoTrace实验室最近开始的两项创新表明，AMS的使用可以扩展到元素周期表中更大的一部分。它们是：(i)使用氟分子阴离子来增加AMS所需负离子的产生；（ii）在冷却和反应细胞中使用射频四极离子导流器，以极低能量消除原子和分子等压线——统称为阴离子等压线分离器（ISA）。

The advantages of accelerator mass spectrometry (AMS), in which isotopes and rare atoms can be measured in sub-milligram samples with sensitivities approaching 1 part in a thousand million million, have been largely confined to elements which readily make negative ions and which have isobars that do not, such as Carbon-14 and Iodine-129. For elements that do not meet one or both of these conditions, the development of analytical strategies has been limited and often been confined to the use of larger accelerators (>5 MV). Two innovations begun recently at the IsoTrace Laboratory have demonstrated that the use of AMS can be extended to a much larger fraction of the periodic table. These are: (i) the use of fluoride molecular anions to enhance the production of the negative ions required for AMS and (ii) the use of radio-frequency quadrupole ion guides in cooling and reaction cells to eliminate both atomic and molecular isobars at very low energies - collectively known as the Isobar Separator for Anion (ISA). These techniques are both at a very early stage in their development; much further work is needed to understand the physical processes involved (i) in the formation of the fluoride molecular anions in the complex chemical environment of the ion source and (ii) in the behaviour of the ions as they traverse the intricate electric fields and cooling and reaction gas regions of the ISA. This knowledge is essential for the application of these techniques to different elements and for their use in reliable analytical procedures and equipment. The establishing of the new AMS facility at the University of Ottawa and, while this facility is in preparation, the continued operation of the IsoTrace equipment provide a unique opportunity to carry out this research and to involve in it the participation of graduate students and post-doctoral fellows both in the generation of this knowledge and the implementation of new applications in a multi-disciplinary setting.