ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
We have developed at LURE a multiwire proportional chamber with a spherical drift space. The wire chamber consists of two cathode planes, comprising 512 wires with a spacing of 1 mm, set on both sides of the anodic plane. The drift space, a gas filled region bounded by two spherically curved electrodes 144 mm apart, offers several advantages: high quantum efficiency, no parallax effect, equivalent spatial resolution in both directions, and smoothing of the pulsed structure of the synchrotron radiation. The gaseous mixture of argon-xenon (58%), ethane (40%), and ethyl alcohol (2%) is circulated in a closed circuit and is continuously purified. Ethyl alcohol, which avoids electrical discharges and sparks, is essential to operate the instrument at high counting rates (〉300 000 events/s). The signal processing, which makes use of one amplifier per cathode wire and of fast priority encoders, determines both coordinates with a resolution of 1 mm and a dead time of 240 ns. Each encoded event is stored into a 512×512 16 bit CAMAC histogramming memory. The experiment is controlled by a PDP11/34 linked to a VAX by a direct memory access channel. A complete set of programs, which performs the data collection and an off line data reduction, is operational. The adaptation of madnes, a general software package which performs an on line data reduction, is under way. Data, collected on a lysozyme crystal to 3.4-A(ring) resolution, give a reliability factor based on intensities of equivalent reflections of 4.7% without absorption corrections; the variation of the detector efficiency is 〈2.7%. A new version of the instrument is under realization. The position encoder, which uses flash ADCs and signal processors, has a resolution of 0.5 mm. Data are stored into a 1024×1024 16 bit VME histogramming memory linked to a micro VAX.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1141036
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