Practical X-ray beam spectrometry with cadmium telluride detector in 10–300 kVp range at Czech Metrology Institute. Part I. Instrumentation

The paper describes instrumentation used at Czech Metrology Institute for measurement of photon fluence spectra directly in X-ray beams. Detector with a cadmium telluride (CdTe) sensor was characterized by means of energy resolution and precise energy calibration. The hole trapping effect in CdTe causing full-energy peak deformations in measured spectra was adopted consisting of analytical models of incomplete charge collection and carrier trapping based on Hecht equation. The detector collimator provided by the manufacturer was modified with additional tungsten shielding that effectively absorbs the majority of photons scattered in the collimator body resulting in significant improvement of the consistency of measured and Monte Carlo simulated detector response. The purpose-made alignment platform increased the accuracy of orientation of the collimator axis improving the measurement in high photon fluence rate beams using collimation disks with very small apertures (down to 100 μm in diameter). The adopted instrumentation and methods for X-ray beam spectrometry enabled to fulfil the requirements of the new ISO 4037:2019-ed.2.0 standard for reference metrology laboratories. Software-focused part dealing with Monte Carlo simulations and procedures for photon fluence spectra unfolding is summarized in [1].