Accelerator Mass Spectrometry

Accelerator mass spectrometry (AMS) is an ultrasensitive technique for measuring the concentration of a single isotope. The electric and magnetic fields of an electrostatic accelerator system are used to filter out other isotopes from the ion beam. The high velocity means that molecules can be destroyed and removed from the measurement background. As a result, concentrations down to one atom in 1017 atoms are measurable.

Many rare isotopes, such as 10Be, 14C, 26Al, 36Cl, 129I, and several interesting isotopes of Uranium and Plutonium are measured with AMS internationally. Currently our research concentrates on the isotope 14C, with applications in arhaeological/historical dating of any carbonaceous material, environmental and atmospheric reseach, and differentiating different sources of carbon. Adding the capability to measure other isotopes is possible.

In 14C-AMS, an electrostatic tandem accelerator and several magnetic and electrostatic analyzers are used to measure the abundance of a rare isotope, 14C in this case. Negative carbon ions are drawn from a graphite sample by cesium-sputtering. The ions are first sorted by a low-energy mass spectrometer, which selects ions of given mass and injects the ions into the accelerator. Due to high velocities, the molecules are destroyed in the center of the accelerator in a column of gas, removing all interfering molecules. After the accelerator, several high-energy spectrometers are used to filter out unwanted background ions from the rare isotope beam. Finally the 14C ions are counted in a semiconductor detector.

Main advantages of AMS as compared to decay counting or laser-based measurements are the high accuracy and sensitivity (0.2% in the best AMS laboratories for a 1-ppt-14C sample) and the small sample size (1 mg for normal samples, can go to < 50 micrograms).

Below is a virtual reality tour around the main parts of our AMS setup. Below that, another video of the lab in general, and an image gallery. These are 360-degree videos, so go ahead and look where you want (grab/drag on the video with your mouse, or tilt your phone).

 

 

 

First ion source (solid-gas hybrid).Second ion source (solid-gas hybrid).Parts of the injector.Injector and top of the accelerator.The TAMIA accelerator tank.Analyzing magnet.Off-axis chamber right after the analyzing magnet.Switching magnet used to select a beamline.The high energy analyzer with a cylindrical electric field.The high energy analyzer with a cylindrical electric field.Rare element detector chamber.Rare element detector chamber.Operator room for TAMIASampling wetland CO2 for 14C measurements.Sampling forest soil CO2 for 14C measurements.Sampling forest soil CO2 for 14C measurements.Sampling forest soil CO2 for 14C measurements.Sampling CH4 from air over a bog for 14C measurements.Sampling wetland CO2 for 14C measurements.Methane sampling during the night.The HASE line for sample pretreatment and graphitization.