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We present a compact, configurable scintillation camera employing a maximum of 16 individual 64-pixel imaging modules resulting in a 1024-pixel camera covering an area of 9.6 cm/spl times/9.6 cm. The 64-pixel imaging module consists of optically isolated 3 mm/spl times/3 mm/spl times/5 mm CsI(Tl) crystals coupled to a custom array of Si p-i-n photodiodes read out by a custom integrated circuit (IC). Each imaging module plugs into a readout motherboard that controls the modules and interfaces with a data acquisition card inside a computer. For a given event, the motherboard employs a custom winner-take-all IC to identify the module with the largest analog output and to enable the output address bits of the corresponding module's readout IC. These address bits identify the "winner" pixel within the "winner" module. The peak of the largest analog signal is found and held using a peak detect circuit, after which it is acquired by an analog-to-digital converter on the data acquisition card. The camera is currently operated with four imaging modules in order to characterize its performance. At room temperature, the camera demonstrates an average energy resolution of 13.4% full-width at half-maximum (FWHM) for the 140-keV emissions of /sup 99m/Tc. The system spatial resolution is measured using a capillary tube with an inner diameter of 0.7 mm and located 10 cm from the face of the collimator. Images of the line source in air exhibit average system spatial resolutions of 8.7- and 11.2-mm FWHM when using an all-purpose and high-sensitivity parallel hexagonal holes collimator, respectively. These values do not change significantly when an acrylic scattering block is placed between the line source and the camera.

The authors characterize a 3/spl times/4 element imaging array consisting of 3/spl times/3/spl times/5 mm/sup 3/ CsI(TI) scintillator crystals individually read out by 3/spl times/3 mm/sup 2/ PIN silicon photodiodes. The array is a prototype for larger modules (16/spl times/16 element) for use in single photon breast cancer imaging. The photodiode output signals are amplified with a 16 channel custom IC (

We have developed low noise, high quantum efficiency photodiode arrays for use with positron-emission tomography (PET). A fabrication process developed for high-energy physics detectors was modified to allow for back-side illumination. A back-side contact consisting of a thin (10 nm) n/sup +/ polysilicon layer covered by an indium tin oxide (ITO) antireflection coating (57 nm) results in >70% quantum efficiency over the wavelength range of 400-1000 nm. The photodiodes are operated fully depleted (300 /spl mu/m thick) resulting in a measured capacitance of 3.2 pF and typical leakage currents of 20-50 pA for a 3 mm square element. At room temperature the noise measured at a shaping time of 4 /spl mu/s is 140 e/sup -/ rms. When coupled to a CsI(TI) scintillator and excited with 141 keV gamma rays, the energy resolution is 12% fwhm.

Preliminary results on 16 CM{sup 2}, position-sensitive silicon drift detectors, fabricated for the first time on p-type silicon substrates, are presented. The detectors were designed, fabricated, and tested recently at LBL and show interesting properties which make them attractive for use in future physics experiments. A pulse count rate of approximately 8 {times} l0{sup 6} s{sup {minus}1} is demonstrated by the p-type silicon drift detectors. This count rate estimate is derived by measuring simultaneous tracks produced by a laser and photolithographic mask collimator that generates double tracks separated by 50 {mu}m to 1200 {mu}m. A new method of using ion-implanted polysilicon to produce precise valued bias resistors on the silicon drift detectors is also discussed.

We have fabricated a 4 cm long, position-sensitive silicon drift detector using high purity, p-type silicon as the starting material. In this paper, we describe the double-sided planar process used to fabricate the detectors and the strategy used to suppress surface carrier inversion due to the presence of fixed positive charge at the Si-SiO/sub 2/ interface. The key issue in optimizing the fabrication process has been to minimize leakage currents and maximize breakdown voltages. Preliminary tests show that a drift signal can be measured across the entire length of the detectors and that the transit time of the holes varies linearly with the position of the induced charge signal. >

Results on the characterization of the electrical properties of amorphous silicon films for the three different growth methods, RF sputtering, PECVD, and LPCVD are reported. The performance of these a-Si films as heterojunctions on high resistivity p-type and n-type crystalline silicon is examined by measuring the noise, leakage current and the alpha particle response of 5 mm diameter detector structures. It is demonstrated that heterojunction detectors formed by RF sputtered films and PECVD films are comparable in performance with conventional surface barrier detectors. The results indicate that the a-Si/c-Si heterojunctions have the potential to greatly simplify detector fabrication. Directions for future avenues of nuclear particle detector development are indicated.

The authors studied the use of neutron-transmutation-doped (NTD) Ge thermistors as phonon sensors at dilution refrigerator temperatures. In addition to measuring their thermal and electrical properties the authors observed pulses generated by X-rays incident on a thermistor thermally well clamped to a heat sink. It is found that during these pulses the lattice temperature of the thermistor apparently does not change. This is interpreted as evidence of a strong coupling between the high-energy phonons generated by the interactions and the charge carriers in the thermistor. The phonons appear to be absorbed within a fraction of a millimeter. It is concluded that the thermistors have several desirable properties for a high-energy phonon sensor. It remains to be seen, however, if a composite detector consisting of a large crystal and attached phonon sensors can be developed. >