Haluk YÜCEL, Doğan BOR, Ayşe Nur SOLMAZ, Asena KURT, Tolga İNAL

Disk kaynak geometrisi için 30-670-keV gama ışını enerji aralığında CdZnTe dedektörünün dedeksiyon verimi

Bu çalışmada, dedektör hassasiyeti, temelde iki parametreye; enerji çözme gücü ve dedeksiyon verimine bağlı olduğundan, belirli bir enerji aralığında CdZnTe dedektörlerin spektroskopik özellikleri incelenmiştir. Bu amaçla, radyoaktif disk kaynaklar kullanılarak bir 5x5x5 mm3 CdZnTe dedektörle elde edilen gama spektrumlarının analizinden enerji çözme gücü (yarı yükseklikteki tam genişlik, YYTG cinsinden) ve pik biçimleri (pik-vadi oranı, P/V cinsinden) belirlenmiştir CdZnTe dedektörünün disk kaynak geometrisindeki dedeksiyon verimi, 30-670 keV enerji aralığında ölçülmüştür. Bu enerji aralığı, medikal görüntülemede kullanılan radyoizotopların, nükleer alandaki zenginleştirilmiş uranyum, plütonyum izotoplarının ve kullanılmış yakıt içindeki aktivasyon/fisyon ürünlerinin yayınladığı X- ve gama ışınlarının hemen hemen tümünü kapsar. Belirli bir mesafeye yerleştirilen disk kaynaklar ile CdZnTe dedektör için gama dedeksiyon veriminin enerjiye bağlılığını gösteren yarı-ampirik fonksiyon önerilmiştir. Ancak ölçülen verim değerlerinde, özellikle yüksek enerjilerde, 200-670 keV aralığında önemli derecede düşmeler gözlenmiştir. Bu durum, esas olarak kristal kusurlarına bağlı olan ve yükün etkin toplanamamasının bir sonucu olarak, fotopik alanlarında kayıpların olduğunu göstermektedir. Bunlar, geleneksel CdZnTe dedektörlerin bilinen yetersizlikleridir.

Detection efficiency of CdZnTe detector in the range of 30-670 keV gamma ray energy for a disc source geometry

The present study is concerned with the measurement of the spectroscopic properties of the CdZnTe detectors in a particular energy range since its sensitivity depends mainly on two parameters: energy resolution and detection efficiency. Thus, the energy resolution (in terms of FWHM) and the peak shape (in terms of peak-to-valley (P/V) ratio) were determined from the gamma-ray spectra measured with a 5x5x5 mm3 CdZnTe detector using radioactive disk sources. The detection efficiency of a CdZnTe detector for a disk source geometry was measured in the energy range of 30-670 keV covering almost most of the X-ray and gamma-ray emissions from the radioisotopes medically used in imaging, the enriched uranium and plutonium isotopes, and some activation/fission products in the spent fuel. A semi-empirical function was proposed to describe the energy dependence detection efficiency of CdZnTe detector for the disk source geometry at a given distance. However, the remarkable decreases in the measured efficiency curve for the detector are found especially in higher energies, above 200 keV up to 670 keV. This indicates that there are the losses in the peak areas associated with incomplete charge collection due to mainly crystal imperfections which can be attributed to the drawbacks existed in the conventional CdZnTe detectors.

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