New CZT Detector Could Aid in Medical Diagnostics, Homeland Security

Security officials have to ensure that unsafe materials are not smuggled into a country by criminals, but it has become quite costly and difficult to detect nuclear substances.

Petrovskite crystal detectors. Image Credit: Northwestern University.
Petrovskite crystal detectors. Image Credit: Northwestern University.

Now, scientists from Northwestern University have designed novel devices based on a cost-effective material to help detect and identify radioactive isotopes.

The researchers used cesium lead bromide in the form of perovskite crystals and successfully designed extremely efficient detectors in small and portable devices for very large detectors and also for field researchers. It took over 10 years to reach these results.

According to Mercouri Kanatzidis, a professor from Northwestern University who headed the study, apart from being less expensive than standard devices, the latest technique developed for identifying gamma rays can easily distinguish between rays of varying energies.

With the novel technique, users can detect legal gamma rays versus the illegal ones. Such detectors are crucial for national security, where they are used for detecting unlawful nuclear materials that are smuggled across national borders. These detectors are also used in both nuclear forensics and medical diagnostics imaging.

Using the perovskite material, we have achieved high resolution in energy detection for gamma rays using a pixelated detector design. This takes us a step closer to creating electronic systems for medical diagnostics and imaging, airport security and more.

Mercouri Kanatzidis, Study Lead and Professor, Northwestern University

The study was recently published in the Nature Photonics journal on December 7th, 2020.

Kanatzidis is also the Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences, and has a joint appointment with Argonne National Laboratory.

In previous studies, the researchers evaluated the performance of the latest cesium lead bromide detector against the traditional cadmium zinc telluride (CZT) detector, and they observed that it performed equally well in identifying gamma rays.

However, new studies that enhanced the sizes of crystals and manipulated pixels instead of planar electrodes have improved the spectral resolution much beyond that of traditional designs, from about 3.8% to 1.4%, identifying energy even from extremely weak sources.

Gamma rays produced by radioactive isotopes slightly vary in energy, often varying by only a few percentage points. The novel material can allow users to detect the source of gamma rays more accurately by pinpointing the variations down to a few percentage points.

Furthermore, the use of even slightly impure materials can usually make detectors non-functional or less efficient, forcing device manufacturers to look for ultrapure CZT to create effective readings.

To the team’s amazement, even their own material could have more impurities by as much 5 to 10 times when compared to CZT and can still perform, rendering it easier and more cost-effective to create. Resolution is equally crucial to medical imaging, such as SPECT scans.

According to Kanatzidis, there is a significant amount of interest in the field, especially considering the safety and cost implications of faulty equipment. But Kanatzidis added that advancements in this field have been rather slow, and this is mostly because investigators target either X-ray and gamma-ray detectors or materials synthesis—his team, however, does both.

Kanatzidis’ laboratory investigated over 60 potential compounds before zeroing on cesium lead bromide. Despite the advancements facilitated by the novel material, Kanatzidis added that the study with colleagues from Northwestern University and Argonne National Laboratory does not end.

Our shelf is full of new possibilities we have yet to investigate more deeply. My research group is a rare combination of the engineering side and the crystal growth side of things.

Mercouri Kanatzidis, Study Lead and Professor, Northwestern University

Yihui He is the first author of the study and a research assistant professor in the Kanatzidis laboratory.

The new device fabrication protocols we report with our collaborators at the University of Michigan could lead to mass production of cesium lead bromide detectors in the near future,” stated Yihui He.

Detector characterization and analysis also involved Professor Zhong He’s team from the University of Michigan. Duck Young Chung, a scientist from the Argonne National Laboratory was a lead collaborator in the study.

Kanatzidis and collaborators have also established a new firm, called Actinia, to market the cesium lead bromide detectors for the detection and identification of gamma and X-rays. The latest detectors will have extensive applications in nuclear safety, homeland security, and medical diagnostics.

The research was financially supported by the U.S. Department of Energy (award number DE-AC02-06CH11357). It was also sponsored by the U.S. Department of Defense (award number HDTRA1-20-2-0002).

Journal Reference:

He, Y., et al. (2020) CsPbBr3 perovskite detectors with 1.4% energy resolution for high-energy γ-rays. Nature Photonics.


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