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A detailed view of the diamond wafers scientists use to get a better measure of spinning electrons. | Photo courtesy of Jefferson Lab.
Diamonds are one of the most coveted gemstones. But while some may want the perfect diamond for its sparkle, physicists covet the right diamonds to perfect their experiments. The gem is a key component in a novel system at Jefferson Lab that enables precision measurements to discover new physics in the sub-atomic realm -- the domain of the particles and forces that build the nucleus of the atom.
Explorations of this realm require unique probes with just the right characteristics, such as the electrons that are prepared for experiments inside the Continuous Electron Beam Accelerator Facility at Jefferson Lab.
CEBAF is an atom smasher. It can take ordinary electrons and pack them with just the right energy, group them together in just the right number and set those groups to spinning in just the right way to probe the nucleus of the atom and get the information that physicists want.
But to ensure that electrons with the correct characteristics have been dialed up for the job, nuclear physicists need to be able to measure the electrons before they are sent careening into the nucleus of the atom. That’s where the diamonds in a device called the Hall C Compton Polarimeter come in. The polarimeter measures the spins of the groups of electrons that CEBAF is about to use for experiments.
This quantity, called the beam polarization, is a key unit in many experiments. Physicists can measure it by shining laser light on the electrons as they pass by on their way to an experiment. The light will knock some of the electrons off the path, where they’re gathered up into a detector to be counted, a procedure that yields the beam polarization.
Ordinarily, this detector would be made of silicon, but silicon is relatively easily damaged when struck by too many particles. The physicists needed something a bit hardier, so they turned to diamond, hoping it could also be a physicist’s best friend.
The Hall C Compton Polarimeter uses a novel detector system built of thin wafers of diamond. Specially lab-grown plates of diamond, measuring roughly three-quarters of an inch square and a mere two hundredths of an inch thick, are outfitted like computer chips, with 96 tiny electrodes stuck to them. The electrodes send a signal when the diamond detector counts an electron.
This novel detector was recently put to the test, and it delivered. The detector provided the most direct and accurate measurement to date of electron beam polarization at high current in CEBAF.
But the team isn’t resting on its laurels: New experiments for probing the subatomic realm will require even higher accuracies. Now, the physicists are focused on improving the polarimeter, so that its diamonds will be ready to sparkle for the next precision experiment.