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


Product Features
  • Lifetime is on the order of 1,000 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 Source of Negative Ions by Cesium Sputtering (MC-SNICS) 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

Two standard sizes of the MC-SNICS are 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.

 

Accessories

The electric cathode press model ECP-890 is designed to pack powdered elemental samples into cathodes (targets) suitable to generate negative ion beams. An electric press provides the user more control over the pressing process than a manual or pneumatic press, improving consistency among cathodes and providing an ergonomic process.

ECP-890

Features:

  • Allows the user to save and restore crucial pressing parameters including the amount of force applied to the cathode material (Target Force) and the length of time it remains at that force (Dwell Time).
  • Designed with an open column structure that allows the compression rod to be cleaned in place, or swiftly replaced with a clean rod.
  • Includes a centering fixture and self-aligning stage, which allow for automatic centering of the cathode with respect to the compression rod
  • Designed with two-hand activation for user safety.

Related Documents
MC-SNICS v1
ECP-890 v1