KCCAMS Facility

Stable Isotrope | AMS Prep Laboratory | Technical Developments at UCI

Keck AMS FacilityThe UC Irvine Keck-CCAMS facility was set up in 2002 with a $2M grant from the W.M.Keck Foundation and matching funds from UC Irvine. The facility consists of three elements:

1. A compact AMS particle accelerator from National Electrostatics Corporation (NEC 0.5MV 1.5SDH-2 AMS system) for measuring radiocarbon (on left).
2. A dedicated companion instrument (Finnegan Delta Plus stable isotope ratio mass spectrometer) for measuring carbon stable isotope ratios ( 13C/12C).
3. A new sample preparation laboratory to supplement existing UC Irvine preparation labs to pre-treat, combust, hydrolyze and graphitize radiocarbon samples.

AMS Particle Accelerator

Keck AMS FacilityThe Keck-CCAMS facility operates a 500 kV compact AMS unit from National Electrostatics Corporation (NEC 0.5MV 1.5SDH-2 – see diagram on the left or go to www.pelletron.com). This unit is similar to the 0.5MV systems in   Zurich,  Georgia and  Poznan, but features improved vacuum (four Cryotorr 8’s) plus additional beam diagnostics and corrective steerers as compared to earlier systems.

Keck AMS FacilityThe system is equipped with the NEC 40-sample MC-SNICS Cs sputter ion source (see left). The negative ion beams produced by the ion source are injected into the accelerator tank using a bounced 90° double-focusing magnet system (injection magnet) to select the appropriated mass. The fast beam switching (bouncer), for sequential measurement of 14C and the stable isotopes 13C and 12C, is performed by varying the bias voltage on the insulated injection magnet vacuum box.

At UC Irvine, we have begun modifying the NEC ion source to increase beam current output, achieve better reliability and improve serviceability to reduce instrument downtime associated with ion source maintenance. Operation at 100-150µA of C is now routine, and currents of 220µA have been observed. More details on ion source development can be found at techinical development.

Keck AMS FacilityThe accelerator terminal contains a high density recirculating gas stripper (2microgram/sq cm of argon), with two turbo pumps for maintaining the best possible vacuum in the accelerator tube (see left). The accelerator tank is filled with high-pressure (80psi) SF6 for isolation of the high voltage terminal.

For maintenance the tank is rolled sideways and the acceleration column is withdrawn from the tank. Maintenance can be carried out by a single person if necessary.

Keck AMS FacilityThe high energy analysis system consists of a 90° double-focusing analyzing magnet and a 90° electrostatic spherical analyzer, which perform an achromatic beam transport of the 14C particles to the detector. The effects of small beam energy variations on beam position cancel in the two elements, leaving the beam centered to the detector. A silicon solid state ionization (above right) detector at the end of the beam line measures particle energies to distinguish 14C from noise.

The measurement of the stable carbon isotopes is performed in the Faraday cup (rightt) chamber (off-axis Faraday cups) after the high energy 90° magnet.

Keck AMS FacilityThe control and data acquisition systems supplied with the instrument are PC-based and use standard nuclear physics and laboratory automation hardware. The system is equipped with beam diagnostics (Faraday cups and beam scanners) to aid in tuning stable isotope beams. Final tuning is carried out by systematically varying critical power supplies to peak up the 14C count rate under computer control. In the unlikely event of malfunction or cooling system failure, the AMS system is programmed to shut down.