A scintillating approach to radiation detection

Radiation detectors are at work every day and everywhere. They inspect cargo at airports, seaports, and border crossings. They discover new forms of matter inside particle accelerators. They collect data in advanced diagnostic technologies used by our doctors and dentists. And they sniff out invisible radioactive gases that leach into our homes.

In 2013, Arnold Burger, a physics professor at Fisk University in Nashville, Tennessee, and collaborators at the Y-12 National Security Complex won an R&D 100 Award—dubbed the “Nobel prize of Technology”—for inventing a novel type of radiation detector: a “high-efficiency thermal neutron detector.” Thermal neutrons play an essential role in nuclear fission, the reaction that powers nuclear plants and atomic bombs. The Y-12 Complex is a manufacturing facility for nuclear weapons components and related defense purposes.

According to Oak Ridge Today, the radiation detector invented by Burger and his collaborators “will be used in handheld nuclear nonproliferation and homeland security applications to find fissile materials….[offering] significant advantages of portability, sensitivity, simplicity, and low cost.”

In 2014, Burger, Y-12 research scientist Ashley Stowe, and Fisk physics professor Michael Groza were approved for a patent that builds on the 2013 award-winning technology. The inventors claim that their improved device requires less detector material and is able to sense radiation simultaneously in two separate but complementary modes. The result is conceivably a more compact, efficient, more accurate, and less expensive detector.

Three types of materials are typically employed in radiation detection: gas-filled tubes, semiconductors, and scintillators. An energetic particle that comes into contact with the first two materials generates a current proportional to the particle’s energy; when it strikes a scintillator, it generates a measurable luminescence, or emission of light.

Helium-3, the gas typically used in gas-tube detectors, is a rare and rapidly depleting resource—so much so that governments are rationing their supplies. The most common semiconductor materials are either expensive, out of range for neutron detection, or difficult to synthesize. Scintillator material is typically less discriminating of thermal neutrons than helium-3.

The invention by Stowe, Burger, and Groza uses a semiconductor crystal of “improved purity and homogeneity.” When impinged by thermal neutrons, the crystal acts as a semiconductor, generating a measurable current; it also acts as a scintillator, generating photons through the neutron’s interaction with lithium atoms in the crystal.

Burger, a winner of previous R&D 100 awards, and the Y-12 facility have been working on their neutron detector technology as far back as 2011, as indicated by this conference proceedings abstract. Whether or not they will win yet another R&D 100 award for their latest design remains to be seen.