Crystals of highly purified thallium bromide were used to fabricate radiation detectors. These detectors were rested with isotopic photon sources and successfully detected gamma and X-rays in the 0.01- to 1 MeV energy range. The detectors were tested at and below room temperature, and their performance approaches that of other semiconductor detector materials which have been under development. The performance of TlBr detectors is due to the similarity in the transport characteristics of electrons and holes in TlBr and the relatively large number of charge carriers produced per unit of energy of detected particle. The performance of these detectors is currently limited by shot noise induced by the leakage current in the TlBr. >

Thallium bromide radiation detectors

Semiconductors photodetectors have long seemed an attractive alternative for scintillation detection, but only recently have semiconductor photodiodes been proven suitable for some room temperature applications There are many applications, however for which the performance of standard silicon p-i-n photodiodes is not satisfactory This article reviews recent progress in two different families of novel semiconductor photodetectors: (1) wide bandgap compound semiconductors and (2) silicon photodetectors with enhanced signal-to-noise ratio The compounds discussed and compared in this paper are HgI 2 , PbI 2 , InI, TlBr, TlBr 1− x I x and HgBr 1− x I x  The paper will also examine unity gain silicon drift diodes and avalanche photodiodes with maximum room temperature gain greater than 10 000

Advances in semiconductor photodetectors for scintillators

Silicon avalanche photodiodes have been fabricated, and their performance as X-ray detectors has been measured. Photon sensitivity and energy resolution were measured as a function of size and operating parameters. Noise thresholds as low as 212 eV were obtained at room temperature, and backscatter X-ray fluorescence data were obtained for aluminum and other light elements. It is concluded that the results with the X-ray detector are extremely encouraging, and the performance is challenging the best available proportional counters. While not at the performance level of either cryogenic silicon or HgI/sub 2/, these devices operate at room temperature and can be reproduced in large numbers and with much larger areas than typically achieved with HgI/sub 2/. In addition, they are rugged and appear to be indefinitely stable. >

High resolution, low energy avalanche photodiode X-ray detectors

In this paper, development of large-area planar avalanche photodiodes (APDs) and monolithic APD arrays for X-ray and scintillation detection is discussed. Single APDs with areas as large as 10 cm/sup 2/ have been fabricated and tested with a CsI(Tl) scintillator (3.8 cm diameter, 2.5 cm height). The resolution of the 662 keV photopeak has been measured to be 9% (FWHM). The X-ray detection performance, gain, and noise of these large APDs have been characterized. Multielement APD arrays have also been fabricated in various formats, such as 4/spl times/4 to 14/spl times/14 elements (2 mm pixels), and the uniformity of gain, noise, and sensitivity has been evaluated for 4/spl times/4 arrays using an /sup 55/Fe source. Timing properties have been measured. Packaging issues related to the APD arrays are discussed.

Large area APDs and monolithic APD arrays

For a better understanding of the performances of X-ray and gamma-ray detectors made of CdTe crystals, the authors have investigated two different operation modes. The first one, the 'type A' solution, has the direction of the bias electric field parallel to the direction of the impinging radiation; the second one, named the 'type B' solution, has the bias electric field perpendicular to this direction. Experimental results and a Monte Carlo simulation applied to type A and B detectors have underlined the advantage of the former configuration for photon energies of the order to 100 keV and of the latter design for photon energies on the order of 500-700 keV, these higher values being typical for medical and industrial applications. Type B detectors of 2.5 mm*2.5 mm*20 mm show a very good energy resolution (full width at half maximum 10 keV for 511 keV and of 11 keV for 662 keV) and an acceptable time resolution (45 ns) even for a preliminary and not-optimized experimental set-up. The Monte Carlo simulation is also described in detail. >

Characterization of small CdTe detectors to be used for linear and matrix arrays

Large area (≈1 cm 2 ) silicon avalanche photodiodes (SiAPDs) have been fabricated and their performance as optical detectors for use with scintillating crystals has been measured. Light sensitivity is measured for hexagonal SiAPDs of 1.57 cm 2 total package area, and the energy and timing resolution is measured for these devices coupled to CsI(Tl) scintillators operating as gamma spectrometers.

Large area silicon avalanche photodiodes for scintillation detectors

A CdTe device structure was investigated for suitability in nuclear medicine instrumentation. These new detectors are room temperature, ?-ray sensors which have good charge collection and response times of 10-20 ns. Devices 0.8 mm to 5 mm thick have been characterized with regard to energy resolution and coincidence time interval resolution.

Properties of a New CdTe Detector for Nuclear Medicine

An automatic exposure controller has been designed that controls the optical film density for film, screen, and radiographic techniques typically used in mammography to within 0.05 over a range of 1.3-6.7-cm thickness of Lucite. This degree of accuracy is better than that reported for presently available controllers. The detector system consists of four cadmium telluride detectors and involves the use of a control algorithm to read the detectors and turn off the mammography unit at the correct time. This algorithm is implemented by a microprocessor, which also provides the means for a convenient calibration.

E. Frederick

Papers

Large area silicon avalanche photodiodes for scintillation detectors

Properties of a New CdTe Detector for Nuclear Medicine

Accurate automatic exposure controller for mammography: design and performance.