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NSRL User Guide

I. Beamline Hardware

Collimators

For some applications we make use of collimators to shape the radiation field. We have a variety of tungsten blocks (largest size: 2”x4”x10”) that can be stacked to produce beam spots from as small as 1 mm2 to 20 cm2 beam spots. These are useful for protecting an incubator from direct exposure to the beam.

An adjustable collimator of 9.5 mm (3/8 inch) thick copper (pictured below) is able to reduce a beam spot to between 10 cm and 0.5 cm in both vertical and horizontal dimensions. While this collimator is easily adjustable, it can only produce rectangular and square beam spots. The list below indicates the beam energies that are completely stopped by this collimator:

  •  Krypton of 285 MeV/u
  • Iron of 352 MeV/u
  • Xenon of 522 MeV/u
  • Gold of 649 MeV/u

For certain applications, pre-assembled static-shape collimators made from layers of Lucite, aluminum and polyethylene are also available. These collimators have precision holes that allow the beam to pass through in selected regions. The holes are typically 5mm to 1cm in diameter and can be square or round. The make-up of the collimator is optimized to stop the beam without producing many penetrating fragments. The Lucite is the first stage with a thickness of 85 mm. Aluminum is the second stage of 75 mm thickness.  The final stage is polyethylene which is 90 mm thick. See images of the collimators below.

When using the layered collimators, it is best to start with heavy ion beams of relatively lower energy, such as 600 MeV/u iron beams. In this way the leakage dose, or dose in the regions covered by the collimator can be kept below about 3% of the dose in the holes. At higher beam energies, the leakage will be greater.

Contact the liaison physicist for special collimation requirements.

Collimator Collimator Collimator Collimator