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ABSTRACT: A high-speed one-dimensional detector for time-resolved small-angle x-ray scattering has been designed and built for experiments at the Advanced Photon Source of Argonne National Laboratory. This detector is made from a 500-μm thick by 150-mm diameter ultra-high-purity n-type silicon wafer. The electrodes, which are a series of concentric rings that are deposited in the wafer, integrate the scattered x-rays over the azimuthal angle and, thereby, produce a one-dimensional detector. This design yields 128 rings, which allows parallel processing of the signal from each ring. The readout electronics consist of transimpedance front-end amplifiers, one for each ring, followed by active pulse-shaping filters. The amplifier signals are digitized using 12-bit analog-to-digital converters, one per ring, which operate at 20 MHz. The frame rate of the system is 271 kHz. Up to 2<sup>20</sup> - 1 scattering profiles may be stored on a random access memory chip and transferred to a data file at a rate of 16 × 10<sup>3</sup> profiles/sec. For X-ray energies between 3.5 and 13.2 keV the efficiency exceeds 80%. The resolving time of the electronics is 300 ns, which is sufficient to isolate electronically a single pulse of scattered x-rays when the synchrotron is operated in a hybrid or asymmetric fill pattern. Therefore, laser-pump/x-ray-probe experiments can be performed without a mechanical shutter. Examples of time-resolved speckle and the kinetics of the formation of sodium chloride particles are presented. This detector is capable of acquiring small-angle x-ray scattering profiles over multiple time scales, which are needed to characterize many chemical, physical, and biological processes. In addition, this detector may be tested and calibrated before experimental runs, without access to an intense beam of x-rays, with alpha particles from a radioactive source such as <sup>241</sup>Am.
IEEE Transactions on Nuclear Science 07/2010; · 1.45 Impact Factor
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ABSTRACT: A new detector for time-resolved small-angle X-ray scattering has been designed and built for experiments at the Advanced Photon Source of Argonne National Laboratory. This detector is made from a 500 mum thick by 150 mm diameter ultra-high purity silicon wafer, which directly converts X-rays into electron-hole pairs. The electrodes are concentric rings that integrate the scattered X-rays over the azimuthal angle. The widths of the rings are optimized for the size of the X-ray beam and its energy spread. Only 128 rings, or channels, are needed to measure a scattering profile. The read-out electronics consist of preamplifiers with pulse-shaping, which are mounted on the detector, and 12-bit, 20 MHz digitizers. The resolving time of the electronics is 300 ns, which is sufficient to isolate a single pulse of scattered X-rays when the synchrotron is operated with a hybrid or asymmetric fill pattern. The data acquisition hardware can average a programmable number of digital samples, up to 64, every 3.68 mus (the period of the synchrotron) to provides a single 12-bit average of the voltage from the analog amplifier chain. The temporal range of the detector is 3.68 seconds or longer and may be controlled by the experimenter. An alpha source is used to calibrate the detector and electronics, and document their performance. Preliminary results obtained during the commissioning of the detector are presented
Nuclear Science Symposium Conference Record, 2005 IEEE; 11/2005
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ABSTRACT: The determination of the structure of transient molecules, such as photoexcited states, in disordered media (such as in solution) usually requires methods with high temporal resolution. The transient molecular structure of a reaction intermediate produced by photoexcitation of NiTPP-L2 (NiTPP, nickeltetraphenylporphyrin; L, piperidine) in solution was determined by x-ray absorption fine structure (XAFS) data obtained on a 14-nanosecond time scale from a third-generation synchrotron source. The XAFS measurements confirm that photoexcitation leads to the rapid removal of both axial ligands to produce a transient square-planar intermediate, NiTPP, with a lifetime of 28 nanoseconds. The transient structure of the photodissociated intermediate is nearly identical to that of the ground state NiTPP, suggesting that the intermediate adopts the same structure as the ground state in a noncoordinating solvent before it recombines with two ligands to form the more stable octahedrally coordinated NiTPP-L2.
Science 05/2001; 292(5515):262-4. · 31.20 Impact Factor
