AN EXTREMELY FAST DIRECT PHOTON COUNTING DETECTOR FOR PROTEIN CRYSTALLOGRAPHY. Ng.H. Xuong¹, P. Datte¹, E. Beuville², T. Earnest²,H. Padmore², J. Millaud², D. Nygrent², Department of Physics, UCSD, La Jolla, CA 92093-0359¹. Lawrence Berkeley Laboratory, Berkeley, CA 94720².

A Smart Pixel Array Detector (SPAD) is being designed which will collect a complete set of monochromatic data for protein crystals in 1.5 minutes and a good Laue picture in less than 10 ms. The readout will also allow framing of up to 16 successive Laue pictures with a switching time of less than 100 us between pictures. The SPAD will consist of 1000 x 1000 pixels of 150 um x 150 um in size¹. The system is being designed around the Column Readout Architecture presently being developed at LBNL². The column readout will allow a photon count rate of 1 million (photons/second) at the pixel and a photon count rate of 8 million (counts/sec/column) total ouput (i.e. up to 8 billion counts per second for the complete detector). Each pixel has its own preamplifier, shaper, discriminator, and a 3 bit prescaler. The material used for the detector will be Si, however we are investigating the use of CdZnTe for measurements that require a larger photon dynamic range or a higher monochromatic photon energy. The data will be stored in real time, in a large histogram memory capable of gathering data for 16 successive pictures. The preliminary results of an 8 x 8 prototype of both Si and CdZnTe will be presented.

¹N.-H. Xuong, P. Datte, E. Beuville, J. Millaud, D. Nygren, "A Very Advanced Detector for Synchrotron Radiation," Proceedings of the 16th European Crystallographic Meeting (ECM 16), August 1995, Lund, Sweden.

²J. Millaud, D. Nygren, "The Column Architecture - A Novel Architecture for Event Driven 2D Pixel Imagers," Proceedings of the Nuclear Science Symposium and Medical Imaging Conference, October 21-28, 1995, San Francisco, CA.