Measurement of Achievable Timing Resolution With ZnO:Ga Films

Abstract

ZnO:Ga films are attractive phosphors for a number of high energy physics and security applications because of their extremely fast temporal response (typically less than 1 ns). Significant efforts have been undertaken to study the dependence of luminescence properties of ZnO:Ga on dopant constituency and temperature. However, most of these studies simply report the decay time of the phosphor, and there is a lack of published values for measured timing resolution with ZnO:Ga. This work aims to present achievable timing resolution with ZnO:Ga through predictive models and experimentally measured values. Careful characterization of a ZnO:Ga sample's temporal distribution and photosensor response provided inputs for an analytical timing model to predict the timing performance of ZnO:Ga. Additionally, the statistical limit on timing performance is calculated via the Cramèr-Rao statistic. The timing performance of a thin-film reference detector is quantified for alpha particle irradiation, and the timing resolution of a ZnO:Ga film is measured against the reference detector. A consistent and precise timestamp from the onset of the rising edge of the ZnO:Ga sample yielded a timing resolution of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$52.5 \pm 10.0$</tex></formula> ps FWHM was measured for the case of 50 detected photons. Good agreement is shown between measured and predicted timing performance, and the relation to the statistical limit is presented. The reported timing performance for a scintillator with an extremely fast decay but poor light yield has meaningful impact in many areas of study where a fast scintillator is required, including its use in the associated particle detector of a neutron generator to enable multimodal, time-of-flight (TOF) based imaging and TOF Positron Emission Tomography Imaging.