Associated particle imaging (API) has been used for the detection of illegal drugs and special nuclear materials, and is also employed in diamond research and space exploration. The technique works by generating neutrons to bombard the sample and measuring the subsequent gamma rays emitted that carry isotopic information about the material.

Unzueta et al. present an API system designed specifically for the measurement of carbon distribution in soil. The device, composed of a sealed-type neutron generator, gamma detectors and a position-sensitive alpha detector, can provide a non-destructive carbon-in-soil measurement for the study of soil-based carbon sequestration techniques, an important arsenal for the fight against climate change.

By using a monolithic yttrium aluminum perovskite scintillator and a sapphire window instead of a fiber-optics faceplate for light transport to the photomultiplier, the device has a similar resolution as existing techniques but with a higher light yield and easier implementation.

The authors characterized the capability of their device to have an angular resolution of 4.5 degrees and a depth resolution of 6.2 cm. They tested the prototype with soil samples and proved it to be sensitive to 12C, 16O, 28Si, 27Al and 56Fe, as corroborated by Monte Carlo simulations.

“Measuring carbon in soil with spatial resolution, non-destructively, and in a short time has always been challenging for scientists and agriculturists alike,” said author Mauricio Unzueta. “The system we developed is a step forward in solving this problem with a technology that has the potential to expand to other applications such as surface composition measurements for space exploration given that we can measure plenty of other elements as well as carbon.”

Source: “An all-digital associated particle imaging system for the 3D determination of isotopic distributions,” by Mauricio Ayllon Unzueta, Bernhard Ludewigt, Brian Mak, Tanay Tak, and Arun Persaud, Review of Scientific Instruments (2021). The article can be accessed at