Ultrahigh-Resolution X-Ray Spectroscopy Using Cyclotron Radiation Emission
Kareem Kazkaz | 20-LW-056
Our goal was to create an ultra-high resolution x-ray spectrometer using cyclotron radiation. Radiation detectors can be compared in various ways, including precision, efficiency, and stability. Depending on the topic that is being studied, a researcher may select one technology over another, so as to have the most robust experiment possible. In the realm of spectroscopy, resolution is a measure of how precise a detector may be—if the energy of two different x-rays is too close for a detector to separate, it can be impossible for the researcher to identify the unique source of the x-ray. The better the detector resolution, the greater the understanding.
Our detector design is based on cyclotron radiation. An x-ray by itself does not emit cyclotron radiation, but if that x-ray is absorbed by an atom, that atom then emits an electron that carries signatures of that x-ray. By trapping the emitted electron in a magnetic field, it in turn emits cyclotron radiation, and the frequency of this radiation provides the original energy of the x-ray. The advantage of cyclotron radiation emission spectroscopy, or CRES, is that it can provide resolution 10 to 100 times better than currently available technologies. In the course of our research, we explored how to build such an x-ray CRES apparatus, including a publication that outlines the challenges and choices that are a part of the detector design. We rehabilitated a 30-year-old high-field magnet to induce the cyclotron motion in the trapped electron. Finally, we assembled the apparatus to look for x-ray induced cyclotron motion. Unfortunately, the global COVID-19 pandemic limited access to the laboratory, and we were unable to exercise the apparatus to verify a CRES signal. We note, however, that the hardware is entirely in hand, and the next step in the research is to exercise the equipment.
Currently available technologies such as crystal diffraction and microbolometers exhibit resolution on the order of 1 electron-volt (eV) or better for low x-ray energies, but their resolution increases as the x-ray energy increases. Because of this, the competing technologies have resolution of 10 to 100 eV for x-rays emitted by heavy elements such as uranium or plutonium. A CRES detector, on the other hand, would maintain its 1-eV resolution even for high-energy x-rays. As such, a CRES x-ray system spans basic science, to nuclear and chemical forensics, to material identification. Thus this system might be applied to gaining a greater understanding of the nuclear structure of heavy elements, or to finding trace evidence of high explosives on a titanium casing. This research advances Lawrence Livermore National Laboratory's core competency in nuclear, chemical, and isotopic sciences, and NNSA missions in such areas as nuclear nonproliferation.
Publications, Presentations, and Patents
Publication: K. Kazkaz and N. Woollett, "Using cyclotron radiation emission for ultra-high resolution x-ray spectroscopy," New Journal of Physics, 23 (2021) 033043. LLNL-JRNL-790159.