Description and specifications of the equipment to be acquired: The following subsections describe the specifications of the equipment to be acquired under BioMERAplusCHEM project in detail. This instrumentation consist of the following three main components: 1) a chemical mapping detector (Silicon Drift Detector [SDD]) for multimodal, correlated XRF and microCT data acquisition at high resolution (micrometers); (2) a laboratory XAFS for speciation data on chemical elements; and (3) a phase contrast data acquisition capability in order to enable data acquisition on samples consisting of adjacent components with similar densities and weak absorption.
Silicon Drift Detector (SDD) for chemical mapping data using XRF: In order to provide correlated multimodal chemical and structural imaging data a Silicon Drift Detector (SDD) with the latest preamplifier technology will be integrated to the existing BioMERA microCT. The microCT will be providing the structural data, while the new SDD will be providing the chemical data. The source has smallest spot size down to 5 micron for measurements on smallest components and microstructures, the Silicon Drift Detectors (SDD) to be integrated has a vacuum preamplifier, low noise, for the energy range upto 10 keV, full width half maxima (FWHM) < 133 eV @ 1 µs peaking time for Mn Kα line, with signal processing electronics and accessories, digital pulse processor board-DPP3 with peaking time down to 25 ns, higher count rates resulting in reduced measuring time and repeatability.
Figure 1: Silicon Drift Detector (SDD)
X-ray Absorption Fine Structure (XAFS) for speciation data: Laboratory based XAFS instrument equipped with an X-ray source covering an energy range from 4.5 to 20 keV. This type of user-friendly spectrometer can be used as an in-house supplement to expensive and limited access to the synchrotron facility beamlines enabling XAFS measurements without using a synchrotron source. In addition to being a competitive alternative, this laboratory instrument is truly complementary to the synchrotron, including where the sample/system needs to be studied over longer time or the samples are prohibited from the synchrotrons for safety reasons.
Technical details: XAFS (hard x-ray monochromator) for high resolution x-ray absorption spectroscopy measurements with crystal analyzers, energy bandpass 600eV, resolving power 4000, constant over the full energy range, acquisition times ~8min, normalized to analyte concentration, x-ray shutter assembly with multipoint safety interlocks. Hybrid photon counting detector for direct detection of x-ray photons combined with single-photon counting, sensor 1028x512 pixels, Pixel size 75x75. No readout noise or dark current for best signal-to-noise ratio. Dual energy discrimination for suppression of low and high energy background. Dead-time free readout.
High-resolution phase contrast microCT imaging data (HR-PCI): Integrating high resolution phase contrast imaging (HR-PCI) capability to the existing BioMERA microCT will overcome limitations of the attenuation-based microCT technique in characterizing weakly absorbing materials. The detection of phase effects in the X-ray that exits a sample along with the attenuated X-ray makes it possible to visualize morphological features in the low absorbing materials like soft tissues, carbon composites, polymers, cloth and any other such materials comprised of low atomic number with weak absorption. Micro-focus sources have sufficient spatial coherence, and propagation-based phase contrast can be observed in the laboratory. With the integration of small pixel detector, 1650 x 1246 to the existing microCT it is possible to visualize phase effects.
Technical details: HR PCI X-ray detector is a lightweight detector for high-resolution X-ray imaging. The detector has gadolinium oxysulphide (Gd2O2S) scintillator screen, placed in direct contact with the photodiode array, converts incident X-ray photons to light, which in turn is detected by the photodiodes. The detector has a resolution of 20 um. The detector has active area of 1650x1246 pixels for imaging. The dynamic range of the detector is 2000:1. The active area of imaging is 33.0 x 24.9 mm. The image read out period is 680 ms.
