Compared to existing flagship cadmium zinc tellurium (CdZnTe) radiation detectors, thallium bromide (TlBr) detectors are highly efficient, cheaper and more compact. Their enhanced performance makes them highly suited to field radiation detection applications and first responder situations.

However, up to now, applications of TlBr have been overshadowed by its susceptibility to detrimental polarization effects. Researchers from CapeSym Inc. have overcome this problem. They report in APL Materials on the use of polarity bias switching schemes to counteract short-term and long-term polarization effects.

Polarity switching schemes minimize the availability of free bromine ions near the metal electrodes and prevent the incapacitation of TlBr detectors for long-term applications. The scheme works by “strategically alternating the voltage polarity after every predetermined interval,” said Amlan Datta, an author of the publication. “[W]e have solved this problem and significantly increased the lifetime of these detectors by stopping the metals from reacting with the bromine.”

The detectors underwent a range of bias switching frequencies (5 to 1660 microhertz) to both maintain and restore the TIBr detector performance at room temperature. Using bias switching, TIBr detectors under two years of continuous operation still performed within prescribed parameters. Polarized TIBr devices were reverted back to their functional detection state within 46 hours, after five days of continuous unidirectional bias operation, using bias switching.

The fully automated device module, containing a TlBr detector and a field effect transistor (FET) input charge amplifier, “not only controls the bias switching intervals, but also keeps track of the TlBr detector health and the applied electric bias history,” said Datta. Detected deviations then alert the user to recalibrate the device or replace the module.

Source: “Stable room-temperature thallium bromide semiconductor radiation detectors,” by A. Datta, J. Fiala, P. Becla, and Shariar Motakef, APL Materials (2017). The article can be accessed at