Crystal Surface Treatment Research Articles

Tapered LSO arrays for small animal PET

By using detectors with good depth encoding accuracy (∼2 mm), an animal PET scanner can be built with a small ring diameter and thick crystals to simultaneously obtain high spatial resolution and high sensitivity. However, there will be large wedge-shaped gaps between detector modules in such a scanner if traditional cuboid crystal arrays are used in a polygonal arrangement. The gaps can be minimized by using tapered scintillator arrays enabling the sensitivity of the scanner to be further improved. In this work, tapered lutetium oxyorthosilicate (LSO) arrays with different crystal dimensions and different combinations of inter-crystal reflector and crystal surface treatments were manufactured and their performance was evaluated. Arrays were read out from both ends by position-sensitive avalanche photodiodes (PSAPDs). In the optimal configuration, arrays consisting of 0.5 mm LSO elements could be clearly resolved and a depth of interaction resolution of 2.6 mm was obtained for a 20 mm thick array. For this tapered array, the intrinsic spatial is degraded from 0.67 to 0.75 mm compared to a standard cuboidal array with similar dimensions, while the increase in efficiency is 41%. Tapered scintillator arrays offer the prospect of improvements in sensitivity and sampling for small-bore scanners, without large increases in manufacturing complexity.

Monte Carlo simulation of a four-layer DOI detector with relative offset in animal PET

We have built a four-layer detector to obtain depth of interaction (DOI) information in which all four layers have a relative offset of half a crystal pitch with each other. The main characteristics of the detector, especially the energy and spatial resolutions, strongly depend on the crystal surface treatments. As a part of the development of an animal PET, we have investigated the effect of crystal surface treatment on detector performances using Monte Carlo simulations in order to optimize the surface conditions of crystals composing a four-layer detector. The proposed detector consists of four LYSO layers with crystal dimensions of 1.5×1.5×7.0 and 1.5×1.5×5.0 mm 3. A simulation tool (DETECT2000) was used and validated against the experimental results; flood images were acquired by a prototype module. Flood images were simulated by varying the surface treatment of the crystals. The optimal surface conditions of the four-layer crystals were derived for a small animal PET with a view towards achieving high sensitivity, as well as high and uniform radial resolution.

New design of a gamma camera detector with reduced edge effect for breast imaging

In recent years, there has been a growing interest in developing small gamma cameras dedicated to breast imaging. We designed a new detector with trapezoidal shape to expand the field of view (FOV) of camera without increasing its dimensions. To find optimal parameters, images of point sources at the edge area as functions of the angle and optical treatment of crystal side surface were simulated by using a DETECT2000. Our detector employs monolithic CsI(Tl) with dimensions of 48.0×48.0×6.0 mm coupled to an array of photo-sensors. Side surfaces of crystal were treated with three different surface finishes: black absorber, metal reflector and white reflector. The trapezoidal angle varied from 45° to 90° in steps of 15°. Gamma events were generated on 15 evenly spaced points with 1.0 mm spacing in the X-axis starting 1.0 mm away from the side surface. Ten thousand gamma events were simulated at each location and images were formed by calculating the Anger-logic. The results demonstrated that all the 15 points could be identified only for the crystal with trapezoidal shape having 45° angle and white reflector on the side surface. In conclusion, our new detector proved to be a reliable design to expand the FOV of small gamma camera for breast imaging.

Design of a high-resolution and high-sensitivity scintillation crystal array for PET with nearly complete light collection

Spatial resolution improvements in positron emission tomography (PET) can be achieved by developing detector arrays with finer resolution elements. To maintain high sensitivity and image quality, the challenge is to develop a finely pixellated scintillation crystal array with both high detection efficiency and high light collection. High detection efficiency means the crystals must be relatively long and tightly packed. Extracting a high fraction of the available scintillation light from the ends of long and skinny crystals proves to be very difficult and there is a strong variation with light source depth. The result is inadequate energy resolution. To facilitate light collection, the crystals must be highly polished, which significantly increases costs and complexity. In this paper, we examine this poor light collection phenomenon in more detail. We also describe a novel solution we are developing for readout of an array of 1 mm crystals using avalanche photodiodes (APD). We demonstrate through optical photon tracking simulations that the crystal light collection for this new design is nearly perfect (/spl ges/ 95 %) and is independent of the crystal length, width, and surface treatment and origin of the light created.

Dual APD array readout of LSO crystals: optimization of crystal surface treatment

We are developing a compact positron emission tomography (PET) detector module with a depth of interaction capability (DOI) based on a lutetium oxyorthosilicate (LSO) scintillator array coupled at both ends by avalanche photodiode (APD) arrays. This leads to a detector with high sensitivity that can provide high and uniform image resolution. We report studies on improving the DOI resolution by optimizing the crystal surface treatment. Six 2/spl times/2/spl times/20 mm LSO crystals were treated with different surface finishes along their length: raw saw-cut, polished optical finish, and chemically etched by hot anhydrous phosphoric acid (H/sub 3/PO/sub 4/) with etching times varying from 1 to 5 min. The ratio of the signals from the two APD arrays was used to measure DOI, and the sum of the signals to measure the total light output. Crystals finished by chemical etching for 2-3 min gave the best overall detector performance, with DOI resolutions ranging from 3.1 to 3.9 mm for events above a 150-keV threshold and uniform light output for different DOI positions. The energy resolution ranged between 14% and 18%. This detector design appears promising for PET applications requiring very high resolution and high sensitivity, for example, in small animal imaging and human breast imaging.

Luminescence detection of phase transitions

Luminescence efficiency, emission spectra and excited state lifetimes are all factors influenced by crystalline phase, pressure and temperature. Discontinuous changes in these luminescence parameters occur during phase transitions of insulating materials whilst simultaneously exciting and heating, or cooling, the samples. Radioluminescence with X-rays emphasises bulk crystal effects, whereas cathodoluminescence can be used to probe changes near to the surface. This review includes examples of new transitions, hysteresis and the value of the method for rapid surveys. Phase changes also occur for impurities and absorbates, when they exist as nanoparticles, these modify the host luminescence and reflect on crystal growth and surface treatments. Impurity effects are apparent even at the ppm level. Examples and the future potential of the method are discussed.

Spatial resolution and depth-of-interaction studies with a PET detector module composed of LSO and an APD array

Detailed results are given for the study of the spatial resolution obtained with different configurations of lutetium oxyorthosilicate (LSO) scintillation crystals read out by a Hamamatsu 2 /spl times/ 8 avalanche photodiode (APD) array. Block detectors as well as small-sized individual LSO crystals have been coupled to the APD matrix. Both one-to-one coupling and light-sharing schemes were investigated. The spatial resolution is derived for each configuration. Two different configurations with two layers of LSO crystals shifted by half a crystal size with respect to each other are used for investigations on the depth-of-interaction information. Prior to the spatial resolution measurements, a comparison of the light output for various crystal surface treatments and different optical coupling materials has been made.

Investigation of a new readout scheme for high resolution scintillation crystal arrays using photodiodes

We are exploring the possibility of using PIN photodiodes to readout the scintillation crystals used in positron emission tomography (PET) detector designs. Semiconductor photodetectors typically have a lower signal to noise ratio than photomultiplier tubes (PMTs). However, they have the advantage of compactness, and, thus, scintillation crystal readout schemes not available to PMTs because of their size and geometry limitations, are readily available to photodiodes. With current PET detector designs, only a small fraction of the available scintillation light, created from 511 keV gamma ray interactions within the crystal, is collected. Scintillation light collection studies were performed for several crystal geometries and surface treatments using both simulations and measurements. In this report, we present a feasible photodiode readout scheme that allows greater than 90% of the available scintillation light created in either BGO or LSO scintillation crystals to be collected by the photodetector. This improvement in light collection with the photodiode readout somewhat compensates for its lower inherent signal to noise ratios and makes it feasible for use in PET detectors. A coincident timing spectrum resolution of 9.4 ns FWHM was measured for 511 keV interactions with one LSO crystal coupled to a photodiode, the other to a PMT.

Collection of scintillation light from small BGO crystals

We propose to develop a high resolution positron emission tomography (PET) detector designed for animal imaging. The detector consists of a 2-D array of small bismuth germanate (BGO) crystals coupled via optical fibers to a multi-channel photomultiplier tube (MC-PMT). Though this approach offers several advantages over the conventional BGO block design, it does require that a sufficient number of scintillation photons be transported from the crystal, down the fiber and into the PMT. In this study we use simulations and experimental data to determine how to maximize the signal reaching the PMT. This involves investigating factors such as crystal geometry, crystal surface treatment, the use of reflectors, choice of optical fiber, coupling of crystal to the optical fiber and optical fiber properties. Our results indicate that using 2/spl times/2/spl times/10 mm BGO crystals coupled to 30 cm of clad optical fiber, roughly 50 photoelectrons are produced at the PMT photocathode for a 511 keV interaction. This is sufficient to clearly visualize the photopeak and provide adequate timing resolution for PET. Based on these encouraging results, a prototype detector will now be constructed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

5.5 Inch video graphic array antiferroelectric display

Abstract Five and one-half inch antiferroelectric liquid crystal panels are fabricated with the resolution of 480 × 640. In the fabrication, combinations of liquid crystal material, alignment layer and surface treatments are investigated. For cell production, several kinds of margins are estimated. They showed that the steepness parameter K is the one of the most important parameters. The optimized multiplex driving scheme to overcome the slow response from the ferroelectric phase to antiferroelectric was also nvestigated.

Photoelectrochemical studies on single crystal [formula omitted] system

PEC studies on single crystal n-CuInS 2 in I 2 I n − (aq.) have been carried out and the results compared with the behaviour of CuInS 2 S n 2− and CuInSe 2 In n − systems. Photopotential, photocurrent vs . applied voltage and wavelength of radiation, power characteristics and output stability of the PEC cell (Pt-counter) show that the photoanode is stable and shows an efficiency η = 4.9%, a value comparable to the CuInS 2 s n 2− , but much less than CuInSe 2 I n − systems. Analysis of the l photo — V data indicate that improvements in η and output stability are possible by suitable control of crystal characteristics, surface treatment and electrolyte modification.

ChemInform Abstract: PHOTOELECTROLYSIS OF WATER WITH SEMICONDUCTOR MATERIALS

AbstractHalbleiter vom n‐Typ korrodieren bei der Verwendung als Photoanoden für die Wasserelektrolyse bei allen untersuchten Elektrodenstrukturen.

Photoelectrolysis of Water with Semiconductor Materials

In an effort to find a semiconductor electrode with a bandgap in the visible part of the spectrum that can serve in the catalytic photodecomposition of water, different systems were explored. The first was sputtered thin films of wide bandgap semiconductor materials such as , , ,, and on low bandgap, n‐type semiconductors such as and. Scanning electron micrographs showed that corrosion is greatly reduced but continues by diffusion of the electrolyte through the film, undermining the film by pit formation in the low bandgap semiconductor. There was no evidence for hole conduction through the film. The second system employed p‐type as the cathode and Pt as the anode. It was observed that this cell catalytically photoelectrolyzes water with conversion efficiency of 0.1%. The efficiency of the device is a strong function of crystal orientation, surface treatment, and purity of the crystal. The results are explained in terms of an energy diagram of the entire system. Areas for possible improvement are mentioned.

Alignmental Deterioration of Homeotropically Aligned Liquid Crystal Cells under d. c. Electric Field. I. Effect of Liquid Crystal Composition and Surface Treatment

Alignmental deterioration in a homeotropically aligned cell was investigated, and the effects of nematic liquid crystal compositions and surface treatments of electrodes on the deterioration were examined. It is concluded that the deterioration rate is determined by the type of ionic doping compound and the surface properties of treated electrodes rather than by the electric conductivity of liquid crystal cells. It was found that the chemical structure of the cation of doping compounds had a strong influence on deterioration. This fact suggests that the deterioration itself is directly related to some catholic electrochemical reaction.

Localized states induced by adatoms on crystal surface

It is shown that in the case of adsorption of less than a monolayer by a) selection of the adsorbate, b) technological treatment of crystal surface with the adsorbate, one may obtain the conditions under which localized states exist.

Multisaturation process revealed by brillouin scattering in CdS

Brillouin scattering of light by sound waves in photoconducting CdS under current saturation conditions gives a fair explanation for the multisaturations of the I–V characteristic. The acoustic flux is spread in the symmetry plane ⊥ to the C axis and is made up of on-axis and of-axis shear phonons respectively responsible for the first and second saturation. Off-axis modes are located in privileged directions which depend on the crystal size and surface treatment. D. L. White's theory explains the whole experimental observation and foresees the occurrence of more than two knees in the I–V characteristic.

Lead telluride-lead tin telluride heterojunction diode array

PbTePb 0·80Sn 0·20Te heterojunction diode arrays have been fabricated from layers grown by the liquid phase epitaxy technique on Pb 0·80Sn 0·20Te substrates. The quality of grown surfaces was found to be dependent upon crystal orientation and substrate surface treatment. Constitutional supercooling has not been identified as a contributing factor. From the capacitance data, an inversion layer is believed to exist at the PbTePbSnTe interface. The diodes exhibit external quantum efficiencies ranging from 15 to 35 per cent without an anti-reflection coating. Junction zero bias impedances vary from 3 to 7 kΩ for a diode are of 6 × 10 −4 cm 2, yielding R 0 A products from 1·8 to 4·2 Ω-cm 2. The average D λ p ∗ at λ p = 10 μ m for an 18-element array is 2·3 × 10 10 cm Hz 1 2 /W for 180°FOV a 300°K background.