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Two by Two Array CCD X-ray Detector

The total active area is 210mm x 310mm. Our modular design permits the tight stacking of this two by two array with no more than a 400 micron wide dead strip between the X-ray sensitive areas  of the four modules. 

Individual Module Specifications:   

The fiber optic taper ratio is 3.6 to 1. 

The CCD being used is the Thomson THX7899 (2K x 2K) chip. After we attach it to the fiber optic taper, we use 2048 x 2048 of these pixels to yield a square format corresponding to the square fiber optic taper in each module. Each pixel is 81.7 microns square at the phosphor (x-ray sensitive area). 

The manufacturer specifies a typical 400,000 electron/pixel full well capacity in MPP Mode.  However, in our experience, we find that the actual full well capacity of the CCD chips we get is in the 450,000 to 500,000 range. The CCD chip used is Grade 1 with the additional specification of no bad columns.  The charge transfer efficiency (CTE) is 99.9995% or better. 

The CCD is run in the low-dark-current MPP mode and is thermoelectrically cooled to  -45 ± 0.1ºC  where dark current is observed at below  0.03 electrons/pixel/second (typically 0.02 e/p/s). 

Since each module has 2048 by 2048 pixels the two by two array has 4096 by 4096 pixels. 

The full width at half maximum of the point response distribution is about 115 microns  (1.4 pixels)  at the phosphor. 

CCD Controllers 

Two by two binning (combining the electric charge from a two by two block of pixels before measuring the total of 2.7 improvement in the above readout speeds, lowering these two times to 3.2 seconds and 1 second respectively with of course, the resulting tradeoff in spatial resolution resulting from the bigger, binned pixels. 

Our proprietary gain control strategy results in a digitization range of 20 bits (1 part in 1,000,000) to help avoid saturation effects and provide accurate measurement of weak reflections in the presence of very strong ones. 

Each controller has a built-in power supply and a precision temperature control circuit for the thermoelectric cooling unit we use to cool the CCD chip in each module. Each controller will be supplied in the specially modified version. The system is supplied with 20 foot electronics cables for connection between the 4 CCD controllers and the detector. 

Equipment Rack

An equipment rack is provided for mounting the four CCD controllers, the Pentium II 400 frame buffer computer and the firewall box.  The rack is about 2.25 meters  (~80 inches) high with wheels, exhaust fan, removable side panels and

Water Chiller

 A  water flow switch is attached to the return line of the water chiller as part of the safety interlock system.  The flow switch will safely shut down the CCD detector electronics through the firewall box if the water flow is interrupted. 

The firewall box is a safety interlock device that protects the Quantum 4 CCD detector from conditions that could damage the four CCD chips.  It protects the detector from power fluctuations,  cooling water flow and vacuum problems. 

The vacuum readout meter monitors the vacuum level and is interlocked to the firewall box.  Should the vacuum pressure reading exceed a preset value the vacuum meter will shut down the detector electronics through the firewall box. 

When mains power is interrupted to the whole detector system, the system will shut down.  When the mains power is restored, the detector system must be restarted by  an operator,  it will not restart by itself when no operator is around. 

Latest Pentium Pro Technology

Raw images are transferred over the network to your UNIX workstation which does "on-the-fly" application of the geometric corrections and the pixel by pixel sensitivity corrections.  In extreme cases where the exposure/readout cycle time is  under 10 seconds these image corrections can be done in some other computer on the network  or else off-line later.  The correction software and the required calibration files are provided and installed with the system. 
Cabling

All required cables to interconnect detector, controllers and computers are  provided and are clearly labeled for the convenience of local staff. 

Modular Software Processes

A full-function graphical User Interface process, running on the workstation, is provided.  Automatic linking to display and data reduction GUI’s is supported.  Run information is entered through this interface. Complete control over binning, ADC speed, and compression options is provided.  In addition, an automatic "inverse-beam" data collection mode is supported with a user specifiable wedge width to facilitate the collection of accurate anomalous data (with minimal chance of user input error).  Kappa goniostat geometry is supported. 

The sensitivity correction begins by the collection of numerous flood images using a calibrated flood field source.  The information for the spatial and geometric corrections is derived from placing a precision mask in front of the detector window and taking several mask images. The flood field and the mask images are then run through ADSC’s proprietary calibration software in which a calibration table is generated for the particular Quantum 210 CCD detector.  This table contains the  information needed to correct for spatial, geometric, and sensitivity errors for this  detector. 

A MOTIF interface to the data reduction package MOSFLM is provided. This user interface now incorporates the new DPS real-space indexing recently developed in Michael Rossman’s laboratory. 

Portability

Documentation