CdTe detector

Since the flow system can be made with such a fast response, it becomes important to improve the response of the infrared detector. Use of a liquid-nitrogen-cooled Hg-CdTe detector, with 200 to 1000 Hz chopping and a lock-in amplifier, permits the IR... 

Because the CdTe detector was not visible through the aluminized mylar film, it was necessary to check for proper... 

A great advantage for CdTe and Hgl2 detectors, " compared to Ge and Si(Li) detectors, is that they can operate at room temperature (see also Sec. 7.5.6). At this time, they can be obtained in relatively small volumes, but they still have an intrinsic efficiency of about 75 percent at 100 keV because of the high atomic number of the elements involved. The energy resolution of CdTe detectors is 18 percent at 6 keV and 1.3 percent at 662 keV. The corresponding numbers for Hgl2 are 8 percent and 0.7 percent. ... 

As with small Ge detectors. X-ray escape peaks are present in spectra taken with these CdTe and Hgl2 detectors. Figure 12.40 shows the spectrum of the 59.5-keV X-rays and y-rays from Am taken with a CdTe detector. The escape peaks due to the K X-rays of cadmium (23 keV) and tellurium (27 keV) are clearly seen. 

In spite of the interest, there have been very few instruments flown with these materials. Only three flight instruments are known to this author, one with a small CdTe detector on ISEE-1 flown in 1977 to study gamma-ray bursts (T. Cline, priv. comm., 1994) and two Hgl2 balloon instruments flown in the early 1980 s (Ricker et al. 1983 Ogawara et al. 1982). None of these had imaging systems. 

Miniature electrically powered Peltier cooling systems are now available to refrigerate items such as small detectors and preamplifiers. At —30°C, the temperatnre is not low enough for HPGe detectors, but adequate for CdTe detectors, giving an impressive improvement in resolution. 

ORTEC s Radiant 2000 CdTe detector, also cooled, uses a method of charge correction (possibly similar to that described above) which corrects pulse heights, rather than rejects them. This particular instrument has an operational range of 10 to 1000 keV and has a resolution of 2.89 keV at 661.6 keV - not much more than twice the width of peaks we might expect from a typical HPGe detector. 

Figure 3.4 Plot showing the spectrum emitted from an 80kVp X-ray tube with a tungsten (W) anode and a 15 keV filter, measured with a 1 mm thick CdTe detector. (Modified from http //www.amptek.com/pdf/ancdtel.pdf) Reprinted with permission from the publisher-John Pantazis.

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