Carry The New Neutron Detector In Your Pocket

Northwestern University and Argonne National Laboratory have developed a new kind of material that might be used in advanced neutron detectors.

As they are able to identify stolen nuclear materials, highly effective neutron detectors play a key role in maintaining national security. At the moment, there are two primary detection technologies available. Helium gas detectors and light flash detectors. These detectors might be as big as a wall in size.

Unlike the first two types, the material created by Northwestern and Argonne is a semiconductor that can absorb neutrons and produce detectable electrical impulses. The detector's semiconductor construction also makes it highly reliable and efficient. It may be used in everything from little handheld field inspection equipment to massive crystal array detectors.

Results will be released in the January 16 issue of Nature.

The study's lead author, Mercouri Kanatzidis of Northwestern University, stated, "Semiconductor neutron detectors have been envisioned for a long time." It was a good idea, but nobody had the resources to make it work.

Currently, Kanatzidis holds the position of Charles E. and Emma H. Morrison Professor of Chemistry in Northwestern University's Weinberg College of Arts and Sciences. He works at both Argonne National Laboratory and elsewhere.

During their disintegration, atoms of heavy elements like uranium and plutonium release neutrons from their nuclei. Most neutron detectors are scintillators, which produce light in response to detected neutrons to serve as a warning to the user. This novel material, a semiconductor, does not generate light but rather senses electrical impulses induced by neutrons. Neutron detectors have several uses beyond just the detection of radiation, including in astronomy, plasma physics, materials research, crystallography, and even the study of stars.

In spite of the fact that conventional thermal neutron detectors have been in use since the 1950s, researchers have been unable to settle on a semiconductor material that reliably detects neutrons. Quickly rising to prominence as the most promising material for neutron detectors, lithium is notable for its exceptional absorption of neutrons. However, keeping lithium stable when it was integrated into a semiconductor was a another story (lithium crumbles when it comes into contact with water).

Nice semiconductors, as Kanatzidis put it, "but they don't have lithium." "On the other hand, there exist stable lithium compounds that aren't good semiconductors. We managed to merge the best features of both systems. One particular isotope of lithium, lithium-6, is a powerful neutron absorber and it's cheap and plentiful to boot."

In their investigation, Kanatzidis and his team found the optimal mix of materials to produce a functional device that maintains lithium stability. Their unique layered lithium-indium-phosphorus-selenium compound is rich in the lithium-6 isotope.

The crystal structure is really special, Kanatzidis said. "The lithium is protected from the elements by many layers that prevent water from penetrating to it. The significance of this aspect of the subject matter cannot be overstated."

As a result, the semiconductor neutron detector can detect thermal neutrons from extremely low-power sources in a matter of nanoseconds. Separation of neutrons from other nuclear signals like gamma rays is also possible. As a result, fewer false alarms will be generated.

Finally, the material is mostly composed of lithium. Since this is the case, a smaller piece of material may absorb the same number of neutrons as a larger device. Therefore, it is now feasible to create portable devices you can hold with one hand.

It's important to have different sized and designed neutron detectors, like our new semiconductor, Kanatzidis said. "You'll need ones that are as tall as a wall yet can be driven around without difficulty. But you'll also need portable, compact ones for use in the field."