HIGH SPEED DIGITAL X-RAY SPECTROMETER WITH TIME RESOLUTION CAPABILITY. W. K. Warburton, B. Hubbard, C. Zhou, X-ray Instrumentation Associates, 2513 Charleston Rd. STE 207, Mountain View, CA 94043-1607

Digitally based, energy dispersive x-ray spectrometer electronics have been developed which allow data to be collected in several time resolved modes to the microsecond time scale. The instrument was first developed for collecting x-ray fluorescence data using multi-element detector arrays at synchrotrons but is readily adaptable to time resolved work using laboratory x-ray sources as well.

Energy dispersive x-ray fluorescence measurements underlie several powerful experimental techniques for studying materials' compositions (x-ray fluorescence analysis: XFA) and their physical and chemical structure at the atomic scale (x-ray absorption spectroscopy: XAS). Arrays of x-ray detectors are becoming popular in these applications as samples become ever more dilute. Our new instrument uses digital processing techniques to implement 4 complete sets of spectrometry electronics, each including a 1000 channel multichannel analyzer, in a single CAMAC module. Each spectrometer is capable of handling input rates of over 500,000 counts/sec with triangular peaking times down to 0.5 us. All setup parameters are digital inputs, including gain, peaking time, pileup inspection values, and detection thresholds. This allows a convenient approach to completely automating all data collection and verification tasks.

The instrument's digital basis also allows x-ray arrival time information to be encoded, allowing the power of x-ray fluorescence measurements to be applied to time dependent phenomena as follows. The module has both a "gate" and a "sync" input, which accept standard TTL pulse or level signals. In time resolved data collection mode, the gate is pulsed each time the experiment is retriggered (e.g. electrically or by laser) and the collected x-rays are tagged with time since the gate pulse. This allows the number of counts within a designated energy window to be binned as a function of time since the trigger. Time resolution to the us level is possible this way.

The module can also count the number of times the sync input toggles following each gate pulse and tag x-rays with this information as well. This allows the x-rays to be binned by this information as well, allowing spectra to be collected synchronously with a modulating sample state (phase locked mode) at rates up to a few 100 kHz. We present an example of EXAFS from a high-T superconductor cycling between its normal and SC states.