Development of Large-Area CdTe/n+-Si Epitaxial Layer-Based Heterojunction Diode-Type Gamma-Ray Detector Arrays
Growth of large area single crystal CdTe layers was studied on <inline-formula> <tex-math notation="LaTeX">$25 \times 25$ </tex-math></inline-formula> mm<sup>2</sup> (211) Si substrates using metalorganic vapor phase epitaxy. High crystalline quality thick crystals with very good material uniformity were obtained. A 2-D monolithic detector array comprising (<inline-formula> <tex-math notation="LaTeX">$20 \times 20$ </tex-math></inline-formula>) pixels was developed and evaluated. Each pixel is <inline-formula> <tex-math notation="LaTeX">$1.12 \times 1.12$ </tex-math></inline-formula> mm<sup>2</sup> size in a 1.17-mm pitch and consists of a p-CdTe/n-CdTe/n<sup>+</sup>-Si heterojunction diode structure, which is isolated from the surrounding pixels by making deep vertical cuts. The detector array exhibited highly uniform and low dark current, typically less than 0.5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula>/cm<sup>2</sup> per pixel at an applied reverse bias of 50 V. The spectroscopic performance was separately confirmed by dicing out a small portion from the array which clearly resolved energy peaks from <sup>241</sup>Am gamma isotopes at room temperature. On the other hand, a significant improvement in the detection property was observed by cooling it to −30 °C.
Synchrotron characterization of high-Z, current-mode x-ray detectors.
Fast x-ray detectors are critical tools in pulsed power and fusion applications, where detector impulse response of a nanosecond or better is often required. Semiconductor detectors can create fast, sensitive devices with extensive operational flexibility. There is typically a trade-off between detector sensitivity and speed, but higher atomic number absorbers can increase hard x-ray absorption without increasing the charge collection time, provided carriers achieve high velocity. This paper presents x-ray pulse characterization conducted at the Advanced Photon Source of x-ray absorption efficiency and temporal impulse response of current-mode semiconductor x-ray detectors composed of Si, GaAs, and CdTe.
Long Ceramic Beam Tubes for Accelerator Magnets
The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.