Multi-Cathode Source of Negative Ions by Cesium Sputtering (MC-SNICS)


Product Features
  • Lifetime is on the order of 1000 hours between source maintenance, except for cathode disk change
  • Cathode disk change time is within one hour from beam on target to beam on target
  • NEC AMS systems equipped with the 134 MC-SNICS have demonstrated radiocarbon ratio measurements for 2000 modern carbon samples to within 2% precision within 5 days

Applications
The Multi-Cathode SNICS (MC-SNICS) source was originally developed as a reliable sputter source for applications that required rapid cathode change and precise, repeatable positioning without cathode exposure to air.  This has proven to be especially beneficial in the field of Accelerator Mass Spectrometry (AMS), where it is used for the production of beams such as Be, I, Cu, Cl, and the actinides.

Design
There are two standard sizes of the MC-SNICS available – one that can accommodate 40 samples at a time, and one that can accommodate 134 samples.

Diagram of operation of the SNICS sourceCesium vapor flows from the cesium oven into an enclosed area between the cooled cathode and the heated spherical ionizing surface.  Some of the cesium condenses on the front of the cathode and some of the cesium is ionized by the hot surface.  The ionized cesium accelerates toward the cathode and is focused on the front face of the cathode.  The ionized cesium sputters particles from the cathode through a condensed cesium layer on the cathode face.  In this way, negative ions are accelerated from the cathode surface.

This is a very similar principle of operation to the single cathode SNICS source, with the exception of using a spherical ionizer instead of a conically shaped ionizer and the addition of an immersion lens and 40 or 134 position cathode disk.

The simple cathode indexing system has proven to be highly reliable.  It is capable of reproducing the cathode position to within 0.002″ of its original position.

Performance
The beam emittance is on the order of 5 πmm mR (MeV)1/2 for optimum transmission through a tandem electrostatic accelerator with proper optics.

Some Negative Ion Beams Produced by the MC-SNICS

Negative Ion Current after analysis
Carbon >100μA
Aluminum >200nA
Beryllium >1.5μA
Iodine ~1μA
Chlorine 30μA
Calcium 80nA

This list is based on data from the NEC factory and contributing laboratories. All ion beam currents listed are measured after 30° or 45° mass analysis.

This is not a complete list of beams that can be produced by the MC-SNICS source. For beam current information for other elements, please contact NEC.


Related Documents
MC-SNICS v1