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Designing an X-ray Collimator

When a star dies in a supernova explosion, radioactive elements are formed and as they decay, they emit gamma rays with short wavelengths and high energies. Included in these radioactive elements formed, are the heavy elements that we’re made of. Being able to study them is important and will allow us to find out how the elements we’re made of are created. A Transition Edge Sensor (TES) is a cryogenic gamma-ray detector that will let us measure gamma-ray energies and will provide an order of magnitude improvement in spectral resolution compared to existing detectors. The goal of this work is to study the uniformity of calibration across the detector by collimating an isotope source to a point in order to hit a small spot on the detector. I designed a collimator in Solidworks that will be mounted on an XY stage to produce a 0.2 mm spot on the detector, with the open end pointed at a Beryllium window on the outside of the cryostat, where the detector is located inside. This way we can check calibration uniformity or any energy variations depending on where the beam is hitting the detector, in order to collect the most precise measurements possible. A spot size of 0.2mm was chosen because we knew we wanted a spot size much smaller than the individual detectors, which are 1.4mm and located inside of the cryostat, 30cm from the Beryllium window. Aiming for a small spot size at a large distance required a source with high activity, so we chose 25mCi of 241Am. Because this involves a radioactive source, the design also had to safely shield radiation, while it’s in use or just sitting in a lab. To help with the design, I wrote a ray tracing code in MATLAB that allowed me to manipulate different variables until the design and its collimation elements were optimized. In this poster I present the design for an x-ray collimator and the initial constraints, calculations and research that lead me to this design.

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