Delay-line anode

Fig. 3.13 MCP with delay-line anode. The position is derived from the delay between A1...

TCSPC channel 1 measures the time of the photons in the laser pulse sequence. It uses the pulse from the low-voltage side of the multichannel plate, which does not depend on the location of the photon. TCSPC channel 2 measures the time between the two ends of the delay-line anode of the detector. The start CFD of channel 2 is gated by the output pulse of the CFD of channel 1. The start pulse of channel 2 is delayed by 10 ns. Consequently, channel 2 starts only for photons that are detected in channel 1. The ADC result of TCSPC channel 2 is used as a channel input signal of TCSPC channel 1. The signal is latched into the channel register after a delay that corresponds to the conversion time of TCSPC channel 2. In the memory of TCSPC channel 1 the photon distribution over t and x builds up. TCSPC channel 2 actually does not need a memory. However, a memory is convenient for building up and displaying the photon distribution versus the x coordinate. 

Another, yet more complicated way to record the spectrally split signal is position-sensitive detection by a delay-line-anode PMT [510], or a resistive-anode PMT [262]. 

Fig. 6.7 Position-sensitive MCP-PMT with delay-line anode...

The drawback of the delay-line-anode detector is that one or two additional TACs and ADCs are required to obtain the X or X-Y information. The electronics for data acquisition are therefore complicated and expensive. This problem may be solved, with some loss in spatial and temporal resolution, by using TDC-based electronics for data acquisition. 

One set of wires, say thex set in Fig. 4.19, is the anode, whereas the perpendicular set is the cathode. The anode set is held at a high positive voltage relative to the cathode set. The wires of each set terminate in a delay line, which delays any signal from a wire in its set by a time interval proportional to the distance of the wire from the end of the delay line. This time delay allows determination of which wire produced the signal. 

The detector operates according to the delay-hne principle. Here a 20 pm thick anode wire and a cathode which consist out of parallel metal strips connected to a delay line are used. The charge creating event induces a signal in the cathode which propagates with a velocity of about 0.2 mm ns in both directions of the... 

In fact, in this method there is no necessity of any other read-out electrode, as for instance in the case of the delay-line technique. This can be certainly an advantage. But unluckily, the highly resistive anode wire shows to be very sensitive to mechanical damage. An occasional high voltage breakdown either destroys the coating or, at least, changes its properties locally and thus the detector response. 

In many applications full two-dimensional information is necessary, and thus fast read-out systems have to be provided. The various techniques, which have been discussed before, have been applied with area detectors. The delay-line read-out has been used with two-dimensional detectors in synchrotron radiation laboratories. At the DORIS-ring in Hamburg an area detector with a 1 mm anode wire distance and a total area of 200 mm x 200 mm is currently in use for measurements of muscle diffraction patterns and for X-ray crystallography The spatial resolution is about (2,5x2,5)mm FWHM. 

Ratio calculation is avoided by using a delay line as an anode of an MCP-PMT [247, 248] (Fig. 6.7). The location along the delay line is obtained by measuring the delay between the outputs at both ends of the delay line. 

The FEE (analogue, e.g. pre-amplifiers etc.) reside in the base of the detector pressure vessel. FEE are devoted to the processing of signals generated by the absorption of X-Rays in the active volume of the MWPC. They comprise a fast spectroscopic amplifier connected in unison to anode wires, together with four cathode pre-amplifiers (Two for each cathode plane). The FEE extract the requisite positional, spectral and temporal information from the MWPC readout system. Moreover, implementation of the fast delay-line readout concept enables a nanosecond discrimination capability. 

All the diffraction results reported in this chapter were obtained using a resistive anode type detector. For those considering new installations, a cathode delay line readout system may be preferable in view of its greater speed and freedom from radiation damage. The detectors discussed so far have all been linear, and this design results in parallax errors with obliquely incident X-ray beams. A better configuration is a detector in the form of an arc of a circle, and these are beginning to be available commercially. 

MWPC) should be used. A full discussion of the design of these is beyond the scope of this chapter, but essentially they consist of orthogonal arrays of anode and cathode wires and the readout is again by delay lines/ They are capable of fairly high count rates (2 MHz) and resolution comparable with the wire spacing ( 1 mm). As yet, a detector of this type has not been used in an electrochemical study. 

Further on, the situation is developing in the following way. After 2-3 days of such operation, delays occur in the intermediate region II while the system passes to the conditions of common anode effect I. Upon a time, these delays become more and more durable, and then osciUatimis appear in the region II, as shown in Fig. 5.17. Oscillations vanish after another 3-5 h of the electrolysis, and then, a few hours later, the system jumps into the conditions of intensive regime represented by line III in Fig. 5.16. Finally, after 4—5 days operation, the anode... 

Neural Stimulation Electrodes and Sensors, Fig. 3 Evoked muscle force as a function of the delay between the primary, cathodic, and secondary, anodic, pulses of a biphasic stimulus. The dashed line represents the force recorded for a single cathodic stimulus pulse. The anodic phase is added to terminate the electrochemistry driven by charge accumulated on the double layer during the cathodic phase. If the anodic phase is applied... 

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