Lutetium Silicate Research Articles

Cluster self-organization of TR-containing silicate and germanate systems: Suprapolyhedral precursors and self-assembly of A2HMTO5 (A = Li, Na; M = Sc, Lu, Yb) crystal structures with MTO5 frameworks

The combinatorial topological analysis is carried out using the coordination sequences method (the TOPOS 4.0 program package) and the matrix self-assembly is modeled for silicates Li2HTRSiO5 (TR = Lu, Yb; space group \(P\bar 1\)) and germanate Na2HScGeO5 (space group P21ab). These compounds, having identical formulas, have different MT frameworks built of M octahedra (TRO6) and T tetrahedra (SiO4, GeO4). New types of crystal-forming binodal nets are discovered: 4 4 6 6 + 4 4 6 for lutetium silicate and 44444(45) + Ge 444(43) for scandium germanate; the atom-site ratio in the nets is M: T = 1: 1. A ring invariant suprapolyhedral precursor cluster composed of four polyhedra is identified, with two (A = Li, Na) atoms lying one above and one below the center of the cluster. A2M2T2 precursor clusters control the evolution of high-level crystal-forming clusters by means of the matrix assembly mechanism. The evolution routes of the suprapolyhedral precursor clusters bifurcate at the stage where topologically dissimilar layers are formed of equivalent chains. The cluster coordination numbers (CCNs) in a layer for the precursor clusters are four for lutetium silicate and six for scandium germanate.

Detector characteristics of the micro crystal element scanner (MiCES)

This work reports on the performance characteristics of detector modules for the micro crystal element scanner (MiCES). MiCES is a small animal PET scanner that is designed for imaging mice. It will consist of four rings of 18 detector modules. The crystal array for each detector is a 22 /spl times/ 22 grid of 0.8 /spl times/ 0.8 /spl times/ 10 mm mixed lutetium silicate (MLS) crystals set at 0.9 mm centers and framed for rigidity to compose a 19.94 mm square. A technique to mount multi-element crystal arrays to position sensitive photomultiplier tubes (PSPMTs) is described. The crystal arrays are slightly larger than the dimensions of the anode strips of the PSPMT. Therefore the detector module assembly requires precise alignment of the crystals with the PMT optics for optimum decoding. The crystal arrays are glued to the PSPMT using Histomount (National Diagnostics) glue. It has excellent transmittance at MLS' peak emission wavelength. In addition, tapping down the crystals while the glue was curing was found to significantly improve the amount of light collected. We introduce a semi-automatic boundary segmentation technique to generate look-up-tables used for decoding the crystal of interaction from the collected PSPMT signals. The algorithm is based on valley detection followed by line segment tracking. The software tool provides a more convenient and precise way to create the crystal map for each detector module. Performance characteristics of each of the first 18 detector modules that were assembled and processed with the described techniques are presented. The overall results are an average energy resolution of 23.8% and an average peak-to-valley ratio of 7.6. These averages, however, include modules that had the crystal arrays removed and re-glued multiple times as part of our learning curve of how to optimize the gluing and positioning procedures.

High efficiency of lutetium silicate scintillators, Ce-doped LPS, and LYSO crystals

Cerium doped lutetium pyrosilicate Lu/sub 2/Si/sub 2/O/sub 7/ (Ce: LPS) scintillator presents high light output (average value: 26,300 ph/MeV), a relatively good energy resolution (10%) and a fast decay time (38 ns) without afterglow. The luminescence efficiency remains very high when the temperature increases up to 450 K. It makes this new scintillator very attractive. We compare its properties to those of another recently developed cerium doped silicate, Ce: Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO).

Elementary Mechanisms behind the High‐Temperature Deformation Behavior of Lutetium‐Doped Silicon Nitride

Intergranular sliding and diffusive mechanisms behind the deformation behavior of a commercially available lutetium‐doped silicon nitride were investigated and discussed. A method of locating and separating phenomena critical for mechanical relaxation at elevated temperatures was applied; the method was based on low‐frequency forced‐vibration damping measurements. The potentiality of lutetium addition for improving the deformation resistance of silicon nitride was clearly reflected in the high‐temperature damping behavior of the investigated polycrystal. Softening of intergranular lutetium silicate phases located at multigrain junctions, which resulted in a grain‐boundary sliding peak, occurred at remarkably high temperatures (>1725 K). This phenomenon, partly overlapping diffusional flow, was followed by further damping relaxation with the melting of the lutetium silicates. Subsequent grain growth was also detected at temperatures >2100 K. Torsional creep results, collected up to 2100 K, consistently proved the presence of a “locking” effect by lutetium silicates with the sliding of silicon nitride grain boundaries below 1873 K.

Industrial manufacturing of cerium-doped lutetium silicate crystals on enterprise joint-stock-company “north crystals”

In lutetium silicate, the presence of two scintillation centers with a different decay time and energy resolution is observed. The influence of heat treatment on the scintillation performances is shown experimentally. Note that the energy resolution is about 4.25%, but there is a strange distribution at the base of the photo peak.

Performance characteristics of micro crystal element (MiCE) detectors

Two micro crystal element (MICE) detector unit designs are evaluated. The detector units are built using highly packed arrays of 0.8/spl times/0.8/spl times/6 mm mixed lutetium silicate (MLS) crystals. The first detector unit, MiCE1, consists of a 5/spl times/5 array of 0.8 mm/spl times/0.8 mm/spl times/6 mm MLS crystals. The detector unit is coupled to four channels of a Hamamatsu multichannel photomultiplier tube (PMT) via a 2/spl times/2 array of 2 mm/spl times/2 mm square optical fibers. The crystal of interaction is determined using simple Anger style logic. Light is shared within the crystal array to help facilitate decoding of the crystals. A full detector module will consist of a 4/spl times/4 array of detector units coupled to a 64-channel PMT. The second detector unit, MiCE2, consists of an array of 0.8 mm/spl times/0.8 mm/spl times/6 mm MLS crystals directly coupled to a 6+6 cross-anode PMT. The crystal of interaction is determined using simple Anger style logic. In both designs, individual crystals are well visualized. Simulations were performed to determine the imaging characteristics of a detector system consisting of MiCE1 detector modules (12.8-cm ring diameter). Results indicate that a detector system built with the authors' MiCE detectors will have an image resolution of less than 1 mm for the central 2 cm of the field of view.

New Lutetium Silicate Scintillators

Cerium-doped lutecium orthosilicate (LSO) is the most promising scintillator discovered in almost five decades. It exhibits a unique combination of important properties for x and gamma-ray spectroscopy: high density, fast decay, and large light yield. However, the practical use of LSO is hindered by difficulties related to its fabrication as a single crystal by the Czochralski method. We report on the usefulness of the sol-gel process in obtaining lutecium silicate scintillators. Upon appropriate drying and firing, lutetium silicate crystals can be grown in a silica matrix. The bulk, polycrystalline transparent scintillators are characterized by XRD, optical absorption, light decay measurement and gamma-ray spectral response. Their properties are comparable to that of traditional LSO single crystals.