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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 demonstrate simultaneous high energy resolution (rms≃800 eV) measurements of ionization and phonons created by particle interactions in a semiconductor crystal of macroscopic size (60 g germanium) at 25 mK. We present first studies of charge collection at biases below 1 V/cm, and find that, contrary to commonly held opinion, the full recoil energy of particle interactions is recovered as phonons when charge trapping is negligible. We also report an unanticipated correlation between charge collection and phonon energy at very low bias, and discuss this effect in terms of charge trapping

A charge coupled device (CCD) image sensor fabricated on high-resistivity silicon is described. The resistivity, about 10,000 /spl Omega/-cm, allows for operation of the CCD with the entire 300 /spl mu/m substrate depleted. This results in better red to near infrared response when compared to conventional and thinned CCDs. In addition the CCD has good blue response when back illuminated. Since the substrate is fully depleted, thinning, with its inherent difficulties, is not necessary in order to enhance blue response.

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. >

In this paper we present new results from the characterization of a fully depleted CCD on high resistivity silicon. The CCD was fabricated at Lawrence Berkeley National Laboratory on a 10-12 K(Omega) -cm n-type silicon substrate. The CCD is a 200 by 200 15-micrometers square pixel array. The high resistivity of the starting material makes it possible to deplete the entire 300 micrometers thick substrate. This results in improved red and near IR response compared to a standard CCD. Because the substrate is fully depleted, thinning of the CCD is not required for backside illumination, and the result presented here were obtained with a backside illuminated device. In this paper we present measured quantum efficiency as a function of temperature, and we describe a novel clocking scheme to measure serial charge transfer efficiency. We demonstrate an industrial application in which the CCD is more than an order of magnitude more sensitive than a commercial camera using a standard CCD.

Most scientific CCD imagers are fabricated on 30-50 (Omega) - cm epitaxial silicon. When illuminated form the front side of the device they generally have low quantum efficiency in the blue region of the visible spectrum because of strong absorption in the polycrystalline silicon gates as well as poor quantum efficiency in the far red and near infrared region of the spectrum because of the shallow depletion depth of the low-resistivity silicon. To enhance the blue response of scientific CCDs they are often thinned and illuminated from the back side. While blue response is greatly enhanced by this process, it is expensive and it introduces additional problems for the red end of the spectrum. A typical thinned CCD is 15 to 25 micrometers thick, and at wavelengths beyond about 800 nm the absorption depth becomes comparable to the thickness of the device, leading to interference fringes from reflected light. Because these interference fringes are of high order, the spatial pattern of the fringes is extremely sensitive to small changes in the optical illumination of the detector. Calibration and removal of the effects of the fringes is one of the primary limitations on the performance of astronomical images taken at wavelengths of 800 nm or more. In this paper we present results from the characterization of a CCD which promises to address many of the problems of typical thinned CCDs. The CCD reported on here was fabricated at Lawrence Berkeley National Laboratory (LBNL) on a 10-12 K$OMega-cm n-type silicon substrate.THe CCD is a 200 by 200 15-micrometers square pixel array, and due to the very high resistivity of the starting material, the entire 300 micrometers substrate is depleted. Full depletion works because of the gettering technology developed at LBNL which keeps leakage current down. Both front-side illuminated and backside illuminated devices have been tested. We have measured quantum efficiency, read-noise, full-well, charge-transfer efficiency, and leakage current. We have also observed the effects of clocking waveform shapes on spurious charge generation. While these new CCDs promise to be a major advance in CD technology, they too have limitations such as charge spreading and cosmic-ray effects. These limitations have been characterized and are presented. Examples of astronomical observations obtained with the backside CCD on the 1-meter reflector at Lick Observatory are presented.

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.

We report on the first measurement of the absolute phonon energy and the amount of ionization produced by the recoil of nuclei and electrons in a 60 g germanium cyrstal at a temperature of \ensuremath{\approxeq}25 mK. We find good agreement between our results and previous measurements of ionization yield from nuclear recoils in germanium. Our device achieves 10:1 discrimination between neutrons and photons in the few keV energy range, demonstrating the feasibility of this technique for large reductions of background in searches for direct interactions of weakly interacting massive particle dark matter.

We report the deposition parameters for optimized a-Si,Ge:H,F alloys in the range of optical (Taue) gap 1.5 leV to 1.62eV. These deposition parameters were optimized using the saturated defect density as a figure of merit. We report initial defect densities at or below 2.5×1016 cm-3, saturated defect densities below 9×1016 cm-3, photoconductivities (at G = 1021 cm-3s-1) between 8.7×10-6 Scm-1 and 7×10-5 Scm-land photosensitivities between 104 and 105 for alloys in this range of optical gap.

We report the deposition parameters for optimized a-Si,Ge:H,F alloys in the range of optical (Taue) gap of 1.22eV to 1.65eV. These deposition parameters were optimized using the photosensitivity and initial defect density as figures of merit. We observe two distinct regimes of film growth rate, dependent on the choice of source gases. Growth from fluoride source gases results in a growth rate of less than 0.6 Ås--1. Growth from a mixture of fluorides and silane gives a range of growth rates from 2 Ås-l to 5.5Ås1. Alloys in both regimes display the low defect densities and the high photosensitivities required for devices.

It is a question as yet unresolved whether the density of light-induced defects in a-Si:H reaches a saturated value that cannot fundamentally be exceeded, or whether the defect density is in all conditions a steady-state value that reflects carrier concentration and temperature. In our experiments on a-Si:H we have observed defect saturation at low temperature and high light intensity; on the other hand, data exhibiting no saturation have also been published. To learn more about this question we have carried out saturation experiments on a-SiGe:H(F) alloys. These alloys have lower defect freeze-in temperatures than a-Si:H and, presumably, lower annealing energies. Therefore, saturation should be more difficult to achieve in the alloys than in a-Si:H.We have studied saturation for a-SiGe:H(F) samples to temperatures above the onset of thermal annealing and have observed that its behavior is similar to that seen in a-Si:H.

If dark matter in the halo is made of weakly interacting massive particles (WIMPs), it may be detected with a cryogenic phonon detector. Such a detector must have low energy threshold, high energy resolution, and, more importantly, good background rejection capability. It has been proposed that a good background rejection ratio can be obtained by a simultaneous measurement of phonons and ionization. To test this experimentally, we have built a 60 g Ge detector and have measured simultaneous phonon and ionization signals, each with 4 keV energy resolution. We present a simple estimate of the rejection ratios, and WIMP event rates that may be achieved by such a detector.

One way to detect dark matter particles from the halo of our galaxy is to detect phonons generated by dark matter particle interaction in a crystal. We report on our efforts to develop a phonon detector operating at 20 mK. We present our recent results on the simultaneous measurement of phonons and ionization, which may provide an effective way to reject background in dark matter search.

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. >