High energy resolution hard X-ray and gamma-ray imagers using CdTe diode devices

TL;DR

This paper reports the development and testing of high-resolution CdTe double-sided strip detectors for hard X-ray and gamma-ray imaging, achieving excellent spectral and spatial performance with novel ASIC readout.

Contribution

The work introduces a new CdTe double-sided strip detector with Pt cathodes, Al anodes, and integrated ASICs, demonstrating improved spectral resolution and imaging capabilities.

Findings

Achieved 400 micrometer spatial resolution.

Obtained 1.8 keV energy resolution at 59.54 keV.

Demonstrated effective gamma-ray imaging spectroscopy.

Abstract

We developed CdTe double-sided strip detectors (DSDs or cross strip detectors) and evaluated their spectral and imaging performance for hard X-rays and gamma-rays. Though the double-sided strip configuration is suitable for imagers with a fine position resolution and a large detection area, CdTe diode DSDs with indium (In) anodes have yet to be realized due to the difficulty posed by the segmented In anodes. CdTe diode devices with aluminum (Al) anodes were recently established, followed by a CdTe device in which the Al anodes could be segmented into strips. We developed CdTe double-sided strip devices having Pt cathode strips and Al anode strips, and assembled prototype CdTe DSDs. These prototypes have a strip pitch of 400 micrometer. Signals from the strips are processed with analog ASICs (application specific integrated circuits). We have successfully performed gamma-ray imaging spectroscopy with a position resolution of 400 micrometer. Energy resolution of 1.8 keV (FWHM: full width at half maximum) was obtained at 59.54 keV. Moreover, the possibility of improved spectral performance by utilizing the energy information of both side strips was demonstrated. We designed and fabricated a new analog ASIC, VA32TA6, for the readout of semiconductor detectors, which is also suitable for DSDs. A new feature of the ASIC is its internal ADC function. We confirmed this function and good noise performance that reaches an equivalent noise charge of 110 e- under the condition of 3-4 pF input capacitance.