CdZnTe detector

Mini multichannel analyzers connected to CdZnTe detectors (MMCC) are the preferred instruments for fi"esh fuel verification giving more credible results than Nal-based systems (Arlt et al. 1993,1997). The probe of the CdZnTe based system is less than 1 cm in diameter and can be inserted into the water tube or control rod guide tube of fuel assemblies and can therefore be implemented entirely in situ without any problems arising from interference resulting from radiation emitted by adjacent fuel assemblies. 

The Fresh MOX Attribute Tester (FMAT) consists of a stainless steel cylinder housing shielding and collimation, a CdZnTe detector and a preamplifier (Aparo et al. 1999). A multiwire cable connects the waterproof measurement cylinder with a data acquisition/ control unit (operated above water). The FMAT is used to verify fi-esh mixed oxide (MOX) fuel stored in spent fuel ponds awaiting loading to the reactor core. It clearly distinguishes between... 

The spectrometric performances of CdZnTe detectors, their robustness, and simplicity are key to their wide application for the verification of irradiated materials in spent fuel (Lebrun et al. 2000 Lebrun and Carchon 2003). 

IRAT requires movement of the spent fuel as the detector approaches the item from the side. IRAT is very similar to FMAT with differences in the coUimator part and the type of CdZnTe detector (O Fig. 63.3). 

The CANDU bundle verifier for stacks (CBVS) moves vertically along the space between columns of trays (10 cm gap) of spent fuel and uses a CdZnTe detector for bundle identification (Ahmed et al. 2001). It employs thick lead shielding to protect the electronics and detector. The CBVS is unable to verify the spent fuel at the bottom layer of a stack due to limited accessibility of a large-size detector part through the funnel structure. During inspection, the tray must be moved. In addition, the large size of the scanning part is both heavy and difficult to handle. 

Amptek cool their CdZnTe detector to —30 °C so that they can increase the bias voltage. This helps charge... 

CdZnTe detectors are necessarily small because of the charge collection limitations. However, for some purposes a small size can be an advantage. One such is plant monitoring, where the abihty to squeeze a detector into small spaces between pipes and valves is a useful asset. 

Arlt, R., Ivanov, V. and Parnham, K. (2000). Advantages and Use of CdZnTe Detectors in Safeguards Measurements (available at http //www.evproducts.com/cz white papers.html). 

An n-type HgCdTe layer 4 is formed on a CdZnTe substrate 3. P-type mesas 61 are formed on the n-type layer. A CdTe layer 8 is formed on the surface of the detector substrate. A capacitor is formed between electrodes 91 and 92 using a layer 10 of CdTe as a dielectric. A resistor is formed from the electrode 91 by a resistor film 10. The resistor is connected to ground potential. 

Fig 5 - A CdZnTe stnp detector fabricated at the Goddard Space Flight Goiter (Parsons et al. 19 ). 

FIGURE 27.12 Solid state imagers. Although Nal(TI)-based scintillation cameras will be the choice for the near future, improvements in solid-state detectors such as CdZnTe may lead to competitive imaging systems. 

Nanocomposite semiconductors such as nanowires arrays of CdZnTe can be used for detecting low-energy gamma rays (Gandhi et al. 2008). The CdZnTe compound semiconductor is electrodeposited in the form of nanowires onto a Ti02 nanotubular template. The preKminary results indicate that the CZT nanowire arrays can be used as radiation detector materials at room temperature with a much lower bias potential (0.7-2.3 V) as compared to the 300-500 V applied to bulk detector materials. 

Most of the pubUshed examples deal with the purity of raw materials (e.g.. In, InP, and GaAs [158] or CdTe [152]), and its change following certain process steps (e.g., the extraction of metallic impurities from CdZnTe) [160] and resulting effects (e.g., contamination levels in GaAs used as radiation detector) [161]. 

The only detectors currently available which are operable at room temperature are the CdTe, CdZnTe and Hglj detectors. However, these are limited in size and are best suited to low-energy photon measurements. 

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