The beamline has four changes in direction, each associated with either an electrostatic analyser (ESA) or a magnet that can be tuned to alter the alignment/direction of the beam.
The principle objective of the AMS is to optimize detection of the rare 14C isotope while minimize problematic detection of stray, interfering particles; hence each major steering component is designed and tuned to remove unwanted molecules from proceeding further down the line, while steering the maximum possible quantity of 14C to the detector. Generally, electrostatic analysers are used to filter out particles that do not have the correct energy and magnets filter out particles of unsuitable mass.
Running a wheel- The structure of our sample wheels is the following: a typical wheel has four run groups: a tuning run group followed by three run groups of eight unknowns.
The tuning run group consists of two blanks, two OX2 standards, and two pairs of secondary standards. Each cathode in the tuning run group is run for four 2-minute exposures. A typical exposure of the OX2 standards produces approximately 45,000 counts at the detector. If the AMS machine is deemed to be running satisfactorily at this point, the tuning run group is transferred to the last run group where all cathodes will be run for four more exposures at the end. All cathodes are run for ten 2-minute exposures.
The unknowns in each run group are normalized to the nearest-in-time runs of bracketing OX2 runs to form the ratio to standard. For more details on how analysis is carried out see here.