Study Of CdZnTe Pixel Arrays Nuclear Detector

CdZnTe(CZT), ternary compound semiconductor, has several advantages: roomtemperature operation and hence no need for liquid nitrogen or Peltier coolers; veryhigh atomic number and high density leading to a good intrinsic detection efficiency;and sturdy detectors that can be packaged compactly in a rugged field instrument. Thereare several disadvantages however, the most important being small size. The ternaryCZT crystals thus far available are limited in size due to physical problems duringgrowth. This small detector size produces a low counting rate compared to other largerdetectors and thus requires a longer counting time for equal statistical precision. Thesmall crystal size also limits the high energy gamma response since higher energygammas, above600keV for example, will have a low interaction probability and willproduce a significantly lower counting rate compared to gammas of300keV. Thislimitation is not all bad however because it applies to background as well. This poorbackground counting rate and results in a better signal to noise ratio for CZT comparedto physically larger detectors. This improves the Minimum Detectable Activity (MDA)for those gamma peaks less than600keV. The CZT crystals do not require extensiveenvironmental protection; they are light sensitive, but not affected by moisture, sosimple packaging is possible. This can be used to advantage in construction of miniaturedetector packages. The simplified packaging needs have also enabled development ofCZT arrays to improve the overall sensitivity.Semiconductor material has always been a good choice for nuclear detection.Through the photoelectric effect, Compton scattering, and electronic effect of thesemiconductor, nuclear radiation received by the semiconductor material can beconverted into electrical signals which can be detected by subsequent electronicprocessing, and the desired spectrum can be captured. This article started from thecharacteristics of semiconductor material, and the corresponding nature andcharacteristics of CZT crystals have been introduced in Chapter2. The advantages anddisadvantages of CZT when being used as the detector in the field of nuclear detectionhave been illustrated from the aspects of CZT material’s growth, defects, and thedamage caused by the radiation. The system built based on CZT has been introduced inChapter3. High-voltage was exerted to CZT to cause the formation of the electric fieldwhich is conducive to the directional flow of the carriers. The electrical signals collected then were exported by special electrode. Finally, the signals after theprocessing of preamplifier and shaping circuit were captured by the electronicequipment, such as the oscilloscope and computer. Chapter4analyzed the effect ofnoise to the entire system in detail. The impact of various factors and thecorresponding theories which were important for the circuit and subsequent processingof signals were researched too. Experiments were performed at the RadiationLaboratory of the3rd Military Medical University. The spectrum of241Am Gammasource was detected by the2×2surface pixel array CdZnTe detection system. Thevoltage of the Gamma source was59.5keV. CdZnTe crystals’ cathode bias was800V,and the detection time was2min. The spectra images of each pixel electrode wereobtained statistically.