Enhanced anion production and isobar separation for accelerator mass spectrometry

加速器质谱法（AMS）是从核物理学发展起来的，在科学领域有许多应用。通过质谱法测量稀有长寿命放射性原子的亚毫克样品大小和较短的计数时间要求必须从离子源所需的高电流中去除稳定的原子等压线。对于14C，负离子的使用消除了离子源处的14N等压线，串联加速器破坏了分子等压线，从而促进了与气候变化、天体物理学、医学和考古学相关的14C测量。由于宇宙射线相互作用或人类使用铀，环境中存在许多其他长寿命同位素。例如，用于地表暴露年代测定的10Be，以及用于追踪海洋环流和追踪核废料储存地点研究的地下水流的长寿命129I。对AMS方法的研究正在进行，目的是改进和扩展AMS到所有长寿命同位素，因为只有三种可以利用负离子不稳定性来完成原子等压线分离。利用超卤素阴离子在离子源上增强等压线的研究已被证明是卓有成效的。在早期的工作中，发现了超离子导体PbF2有助于生成许多超氟阴离子，如AlF4-、SiF5-、PF6-等。一项NSERC资助的I2I提案，在串联加速之前使用射频四极化学反应电池进行阴离子的广泛等压分离，已经成功进行了初步测试。这导致在不需要大型加速器的情况下检测低水平的36Cl和41Ca。在与工业界的合作下，这一发展有望使离子源附近的等压选择商业化，从36Cl开始，以及提供关于超阴离子、阴离子和离子-气体化学反应性质的许多有用信息。

Accelerator Mass Spectrometry (AMS), which developed from nuclear physics, has many applications in the Sciences. The sub-milligram samples sizes and the short counting time for the measurement of rare long-lived radioactive atoms by mass spectrometry require that stable atomic isobars must be removed from the high currents needed from the ion source. For 14C, the use of negative ions eliminates the 14N isobar at the ion source and a tandem accelerator destroys the molecular isobars, thereby facilitating 14C measurements relevant to climate change, astrophysics, medicine and archaeology. As a result of cosmic ray interactions or the human use of uranium many other long-lived isotopes are present in the environment. Examples are, 10Be, used for surface exposure dating, and long-lived 129I, used to trace oceanic circulation and to trace underground water flow for Nuclear Waste Storage site studies. Research into the AMS method is being carried out with the aim of improving and extending AMS to all long-lived isotopes, as only three can exploit negative ion instability for complete atomic isobar separation. The study of isobar enhancement at the ion source by means of superhalogen anions has proved very fruitful. During earlier work the efficacy of the super-ionic conductor PbF2 for helping to generate many of the super fluoride anions such as AlF4-, SiF5-, PF6- etc was discovered. An NSERC funded I2I proposal, which uses RF quadrupole chemical reaction cells for the generalised isobar separation of anions prior to tandem acceleration, has had successful initial tests. This has led to the detection of 36Cl and 41Ca at low levels without the need for large accelerators. In collaboration with industry, this development promises to make isobar selection near the ion source commercially available, starting with 36Cl, as well as providing much useful information on the properties of the super-anions, dianions and ion-gas chemical reactions in general.