RESUMEN
We report on the implementation of an algorithm and hardware platform to allow real-time processing of the statistics-based positioning (SBP) method for continuous miniature crystal element (cMiCE) detectors. The SBP method allows an intrinsic spatial resolution of ~1.6 mm FWHM to be achieved using our cMiCE design. Previous SBP solutions have required a postprocessing procedure due to the computation and memory intensive nature of SBP. This new implementation takes advantage of a combination of algebraic simplifications, conversion to fixed-point math, and a hierarchal search technique to greatly accelerate the algorithm. For the presented seven stage, 127 × 127 bin LUT implementation, these algorithm improvements result in a reduction from >7 × 10(6) floating-point operations per event for an exhaustive search to < 5 × 10(3) integer operations per event. Simulations show nearly identical FWHM positioning resolution for this accelerated SBP solution, and positioning differences of <0.1 mm from the exhaustive search solution. A pipelined field programmable gate array (FPGA) implementation of this optimized algorithm is able to process events in excess of 250 K events per second, which is greater than the maximum expected coincidence rate for an individual detector. In contrast with all detectors being processed at a centralized host, as in the current system, a separate FPGA is available at each detector, thus dividing the computational load. These methods allow SBP results to be calculated in real-time and to be presented to the image generation components in real-time. A hardware implementation has been developed using a commercially available prototype board.
RESUMEN
We report on the implementation and hardware platform of a real time Statistics-Based Processing (SBP) method with depth of interaction processing for continuous miniature crystal element (cMiCE) detectors using a sensor on the entrance surface design. Our group previously reported on a Field Programmable Gate Array (FPGA) SBP implementation that provided a two dimensional (2D) solution of the detector's intrinsic spatial resolution. This new implementation extends that work to take advantage of three dimensional (3D) look up tables to provide a 3D positioning solution that improves intrinsic spatial resolution. Resolution is most improved along the edges of the crystal, an area where the 2D algorithm's performance suffers. The algorithm allows an intrinsic spatial resolution of ~0.90 mm FWHM in X and Y and a resolution of ~1.90 mm FWHM in Z (i.e., the depth of the crystal) based upon DETECT2000 simulation results that include the effects of Compton scatter in the crystal. A pipelined FPGA implementation is able to process events in excess of 220k events per second, which is greater than the maximum expected coincidence rate for an individual detector. In contrast to all detectors being processed at a centralized host, as in the current system, a separate FPGA is available at each detector, thus dividing the computational load. A prototype design has been implemented and tested using a reduced word size due to memory limitations of our commercial prototyping board.
RESUMEN
Molecular clusters of BBr3 were subjected to electron ionization and mass analysis in a reflectron time-of-flight mass spectrometer. Five series of cluster ions were observed, with formulas corresponding to each of the possible fragment ions of BBr3 being solvated by neutral BBr3 molecules. Geometry optimizations on the observed cluster ions using density functional theory (B3LYP/6-31G*) predict that fragment ions smaller than BBr3+ undergo reactions with neutral BBr3 molecules to form covalently bound adduct species that function as core ions within the clusters. Once all boron atoms are saturated, the reactions cease, and larger cluster ions consist of BBr3 molecules loosely bound to the core ions. Divalent bromine atoms are present in at least three of the cluster ions, and most of the intermolecular contact within the clusters is between Br atoms. Enthalpies of formation, addition reactions, and BBr3 elimination from the cluster ions were derived from B3LYP and MP2 calculations at the B3LYP/6-31G* geometries using both the 6-31G* and the 6-311++G(2df,2p) basis sets. The results are compared to limiting expectations based on known bulk thermochemistry.