X-ray characterization of a multichannel smart-pixel array detector

The Voxtel VX-798 is a prototype X-ray pixel array detector (PAD) featuring a silicon sensor photodiode array of 48 × 48 pixels, each 130 µm × 130 µm × 520 µm thick, coupled to a CMOS readout application specific integrated circuit (ASIC). The first synchrotron X-ray characterization of this detector is presented, and its ability to selectively count individual X-rays within two independent arrival time windows, a programmable energy range, and localized to a single pixel is demonstrated. During our first trial run at Argonne National Laboratory's Advance Photon Source, the detector achieved a 60 ns gating time and 700 eV full width at half-maximum energy resolution in agreement with design parameters. Each pixel of the PAD holds two independent digital counters, and the discriminator for X-ray energy features both an upper and lower threshold to window the energy of interest discarding unwanted background. This smart-pixel technology allows energy and time resolution to be set and optimized in software. It is found that the detector linearity follows an isolated dead-time model, implying that megahertz count rates should be possible in each pixel. Measurement of the line and point spread functions showed negligible spatial blurring. When combined with the timing structure of the synchrotron storage ring, it is demonstrated that the area detector can perform both picosecond time-resolved X-ray diffraction and fluorescence spectroscopy measurements.

High Brightness Beam for Microcrystallography at GM/CA@APS

GM/CA is a world leader in the development of microcrystallography capabilities for biological macromolecules. The combination of the GM/CA-developed quad-mini-beam collimator and advanced rastering and vector collect software tools have revolutionized microcrystallography. Recently, beamline 23ID-B was reconfigured by shifting the focusing optics 3.8 m downstream. This significantly increased the source demagnification and led to a 4-fold increase in the 5- and 10-micron beam intensity. Beamline 23ID-D is also being upgraded. A Pilatus3-6M with a 1.0 mm thick X-ray sensor was commissioned in January 2014 allowing shutterless data collection with high S/N. The detector specifications include 100 Hz frame rate, 10 MHz/pixel count rate, and high X-ray efficiency. The beamline optics and endstation are also being upgraded to provide a high intensity beam whose size can be variable rapidly in the range of 1 - 20 micron, a new air bearing goniometer with a sphere-of-confusion (SOC) of ~100 nm, a miniature sample XYZ stage that allows centering and scanning of a micron-sized crystal, and a new on-axis-visualization system that provides high resolution optical images of sample crystals. Plans are being developed to upgrade the Advance Photon Source storage ring with a Multi-Bend Achromat lattice. The source properties will be dramatically improved primarily by reducing the horizontal source size to be comparable to the vertical source size, resulting in a 2-3 orders of magnitude increase in source brightness. Both beamlines will be significantly improved by the source upgrade. Moreover the new microfocusing optics for 23ID-D will fully exploit the new source and could deliver a 500 nm (FWHM) beam with >2e13 photons/sec. This unprecedented flux density will provide new opportunities and challenges, and allow the study some of the most important problems in biology. Details of these developments will be presented.