Let’s dive into the processes going on inside one the most unique labs at UC Davis and in the U.S.
By EKATERINA MEDVEDEVA — science@theaggie.org
In the southeast part of the UC Davis campus, amid numerous complexes dedicated to sciences, there stands an inconspicuous yellowish building named the Jungerman Hall. Despite its plain appearance, the Crocker Nuclear Lab (CNL) concealed beyond its doors is truly exceptional.
At the center of all the processes happening in CNL is the 76-inch isochronous cyclotron that accelerates particles. It is “one of the few of its kind still in use,” according to the CNL webpage. Unlike most modern cyclotrons, the CNL cyclotron can be tuned at relatively low energy levels within the range of four MeV to 67.5 MeV, enabling it to operate without energy degraders and produce a “high quality, stable beam [of particles] with lower energy spread and emittance.”
So how does it accelerate the particles? At the very core, a cyclotron can be pictured as a hollow vacuum disk with an electric voltage applied across its two insulated halves (called the Ds). When a charged particle (usually a proton, deuteron, helion or alpha) is placed inside, it is attracted to the half with the opposite charge, meaning that the force of the electric field accelerates that particle in its direction. At the same time, a magnetic field that is applied through the plane of the disk causes the particle to experience centrifugal force, turning it around on an arc and returning it back to the center axis.
At this point, the polarity of the Ds switches so that the particle always finds itself in the half with the opposite charge. However, now that it has some velocity, it goes around on an even bigger arc due to the force of the magnetic field. As this process goes on, the particle gains velocity and spirals further out of the center until it reaches the edge of the disk and is allowed to escape.
One particle, of course, would not be able to do much, so numerous particles are accelerated and allowed to escape in beams. When they leave the cyclotron, but still remain in a vacuum chamber, these beams are “steered and focused by magnetic elements” manipulated from the control room and are transported to the beam line. There, they are collimated (parallelized) and directed toward their final target, as described by the 2001 Institute of Electrical and Electronics Engineers (IEEE) Radiation Effects Data Workshop record.
The applications of this technology at CNL are broad, ranging from treatment of ocular melanoma (a rare type of eye cancer that forms behind the retina) to testing the effects of cosmic radiation on the electric equipment used in space missions.
One of the most notable examples of the latter is the testing of Focal Plane Arrays (FPAs) for the James Webb Space Telescope (JWST), which are critical light sensors used for imaging. The research team conducting these tests simulated conditions of cosmic radiation using the CNL cyclotron, irradiating the devices at varying angles of incidence and then evaluating their sensitivity to make sure that they pass the set benchmarks to be used for JWST.
The CNL cyclotron is also used for other projects including the production of Astatine-211 (a cancer treating isotope), development of detectors to look for dark matter and many more applications.
Recently, the UC Davis Physics Club teamed up with CNL and other initiatives to conduct tours of the laboratory. They were led by the Director of the CNL and Professor in the Department of Physics and Astronomy, Dr. Eric Prebys, as well as graduate students Logan Knudson and Lena Korkeila.
To learn more about the UC Davis Physics Club, check out their website and Instagram page. If you haven’t had a chance to visit the Crocker Nuclear Lab, you can find a short tour posted on Dr. Eric Prebys’ YouTube channel and more information on the CNL webpage.
Written by: Ekaterina Medvedeva — science@theaggie.org
