Suter Martin
Laboratory of Ion Beam Physics, ETH Zürich, Schafmattstrasse 20, Zürich, Switzerland.
Eur J Mass Spectrom (Chichester). 2010;16(3):471-8. doi: 10.1255/ejms.1078.
Accelerator mass spectrometry (AMS) was invented for the detection of radiocarbon at natural isotopic concentrations (10(-12) to 10(-15)) more than 30 years ago. Meanwhile this method has also been applied for the analysis of many other long-lived radioisotopes, which are found at very low concentrations. The first investigations were made at large tandem accelerators originally built for nuclear physics research and operating at voltages of 6-12 MV. Today dedicated instruments are mostly used for AMS, which are optimized for associated applications. In the past 15 years, a new generation of much smaller instruments has been developed. For many years it was believed that accelerators with voltages of 2 MV or higher are needed to eliminate the molecular interferences. At these energies the ions are predominantly stripped to charge state 3+, thereby removing the binding electrons of the molecules. In contrast, the new compact facilities use 1+ or 2+ ions. In this case the molecular destruction process is based on molecule-atom collisions in the gas cell. The cross sections for this destruction are sufficiently large that the intensity of molecular components such as (12)CH(2) and (13)CH can be reduced by 10 orders of magnitude. These new facilities can be built much smaller due to the lower energies. Universal instruments providing analysis for many isotopes over the whole range of periodic table have a space requirement of about 4 x 6 m(2); dedicated radiocarbon facilities based on a 200 kV accelerator have a footprint of about 2.5 x 3 m(2). This smallest category of instruments use special technologies: The high voltage terminal with the gas stripper canal is vacuum insulated and the gas is pumped to ground potential through a ceramic pipe. A conventional 200 kV power supply provides the terminal voltage from outside. A review of this new generation of compact AMS facilities is given. Design considerations and performance of these new instruments will be presented. With these developments, new AMS instruments are not much larger than conventional mass spectrometers, allowing a significant reduction in cost.
加速器质谱法（AMS）是30多年前为检测自然同位素浓度（10^(-12)至10^(-15)）下的放射性碳而发明的。与此同时，该方法也已应用于许多其他低浓度长寿命放射性同位素的分析。最初的研究是在最初为核物理研究建造的大型串联加速器上进行的，这些加速器的运行电压为6 - 12兆伏。如今，专用仪器大多用于AMS，这些仪器针对相关应用进行了优化。在过去15年里，新一代体积小得多的仪器得到了发展。多年来，人们一直认为需要2兆伏或更高电压的加速器来消除分子干扰。在这些能量下，离子主要被剥离到3 + 电荷态，从而去除分子的束缚电子。相比之下，新型紧凑型设备使用1 + 或2 + 离子。在这种情况下，分子破坏过程基于气体池中分子与原子的碰撞。这种破坏的截面足够大，以至于诸如(12)CH(2)和(13)CH等分子成分的强度可以降低10个数量级。由于能量较低，这些新设备可以建造得小得多。能够对元素周期表整个范围内的许多同位素进行分析的通用仪器空间需求约为4×6平方米；基于200千伏加速器的专用放射性碳设备占地面积约为2.5×3平方米。这类最小的仪器使用特殊技术：带有气体剥离通道的高压终端采用真空绝缘，气体通过陶瓷管抽到地电位。传统的200千伏电源从外部提供终端电压。本文对新一代紧凑型AMS设备进行了综述。将介绍这些新仪器的设计考虑因素和性能。随着这些发展，新型AMS仪器并不比传统质谱仪大多少，从而显著降低了成本。
