DETECTOR DEVELOPMENT AND UPGRADE

Brookhaven Science Assoc-Brookhaven Lab, Upton NY

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objectives [unreadable]The objectives stated in the recent renewal proposal are these: upgrade our two existing Area-Detector Systems Corp. (ADSC) Q315 detectors, initiate the purchase of a modern pixel-array detector (PAD) that is at the state of the art, contribute to and participate in a detector-development program (monolithic, highly-integrated modules). Although they were favorably reviewed, we did not receive funding for the last two projects. We report on the PAD purchase only because we're looking for other avenues, and we do not report on the third project here. Diffraction patterns of macromolecular crystals are collected at all five of the PXRR beamlines with the excellent CCD-based area detectors from Area Detector Systems Corporation. Two of these are Q315s deployed on our undulator beamlines X25 and X29, one is a recent model Q210 at the X12C bending magnet beamline, and two are slow, first generation Q4 detectors at X26C and X12B. Not surprisingly, users and staff strongly prefer performing experiments with the three newer detectors that complete image readouts in about one second, and they hesitate to wait the 15 seconds that it takes a Q4 to render its image. More than impatience of users, this emphasis on speed reflects the advanced status of data collection methods as well as the high level of experimenter training in fast crystallographic decision-making. Results [unreadable]In summer 2008 we sent one of our Q315 detectors [unreadable]the second one, purchased in 2002 [unreadable]for factory upgrades to Q315r specifications. It was equipped with new internal readout electronics and new thermo-electric coolers that now can keep the CCDs at the required low operating temperature. New image gathering computers replaced obsolescent ones. When re-commissioned at X29, we confirmed that the gains in the standard 2x2 hardware binned readout mode met expectations and, including goniometry overhead, achieved a readout in 0.8 seconds, down from the original 1.4s. This compares well to typical exposure times of 1 sec or less at the X29 undulator line. Careful reduction of numerous user data collections by Dr. H. Robinson at X29 revealed that the signal-to-noise ratio had improved when compared to similar studies carried out before the upgrade. These important gains for the measurement of weak reflections are consistent with a manufacturer-specified 30% reduction of the electronic read noise. Meticulous inspection of individual diffraction patterns also led him to discover a small imaging artifact caused by strong, saturating Bragg reflections. Though inconsequential in data reduction, it helped ADSC to find the electronic cause of this imperfection and to revise their circuitry. Given the verified performance gains achievable through detector upgrades, we have scheduled the refurbishment of our second Q315, purchased in 2000, and serving X25. We have succeeded in building a Linux-based EPICS IOC to control all of our ADSC detectors. This method uses the areaDetector module written by at the APS, and replaces the image-gathering process that used to be part of the CBASS experiment-control program. While a side product of introducing digital-video cameras for crystal observation, this effort is an important step towards unifying all device controls under EPICS, achieving fast and parallel command transmissions (see Plans.) Plans [unreadable]We endeavor to acquire a pixel array detector (PAD) for use on one of our undulator beam lines to provide higher quality data, faster, to users and Mail-in staff and clients. Because this specific aim was favorably reviewed, but not funded in our grant renewal, we teamed up with Dr. H. Li, our collaborator at Stony Brook University, and will submit a S10 High-End Instrumentation grant proposal for the acquisition of a PAD. In the year ahead, we will extend EPICS control to the specimen spindle and the shutter. When this combined hardware and software project is complete, diffractometer, goniometer, and detector functions can be managed in parallel using the object-oriented EPICS control architecture. For diffractometer operation with current model CCD detectors, a reduction of the shutter-to-shutter pause will be obtained, bringing us closer to the image readout time limit imposed by detector technology. More importantly, unifying controls into one self-contained system essentially provides the technology and methods that we will need to develop and evaluate shutter-less data collections with continuous spindle rotation of the kind we would deploy with a pixel array detector. Significance [unreadable]Once a pixel array detector becomes available on an NSLS undulator beamline, we will achieve dramatic gains in data quality and quantity beyond those possible with CCD-based detectors. Owing to the fast framing rate of 12 Hz, the astonishingly short readout dead-time of less than 4 ms, the complete discrimination against background to zero values, and the unitary point spread function, fine slicing data collection methods can be employed during a shutter-less continuous sweep of the crystal spindle. This entirely new method provides data-reduction and indexing programs with sharply defined, and narrowly boxed, Bragg spots over an unprecedented dynamic rage, thus yielding more complete, crisper datasets at higher resolution, and ultimately better structures.