Gas-filled detectors

With gas-filled detectors, a chopped light system is normally used in which one side of the detector sees the source through the analyzing beam and the other side the reference beam, alternating at a frequency of a few hertz. 

The effect of an absorbed x-ray quantum on a photographic plate is visible as metallic silver after the plate has been developed and fixed. The number of quanta absorbed help to determine the amount of this metallic silver, and the development process performs somewhat the same function as amplification in a gas-filled detector (2.5). 

Fluorescence effects are, in general, considered to be negligible. In gas-filled detectors the corresponding photons are discarded in the energy discrimination stage of... 

A variety of detectors is used in the field of X-ray scattering. In fact, the proper choice of the detector (as well as the sample thickness) is essential for good quality of the recorded data, whereas the intensity of the synchrotron radiation determines the minimum cycle time between two snapshots - if a modern CCD detector is used. Gas-filled detectors cannot be used to record high-intensity scattering patterns. Image plates need a minimum time of 2 min for read-out and erasure. 

Gas-filled detectors are the classical X-ray detectors. The main advantages are... 

These features made gas-filled detectors the limiting factor for effective use of synchrotron beamlines. Nevertheless, they are still well-suited for laboratory equipment10. Gas-filled detectors are classified by their dimensionality. 

If the progress of laboratory X-ray sources continues, gas-filled detectors will probably be replaced by image plates with automatic read-out. 

SUMMARIZE radiation protection principles to include definition of terms, types of radiation, and the basic operation of a gas-filled detector. 

A gas-filled detector is used to detect incident radiation. 

EO 1.4 DESCRIBE the principles of operation of a gas-filled detector to include ... 

The pulsed operation of the gas-filled detector illustrates the principles of basic radiation detection. Gases are used in radiation detectors since their ionized particles can travel more freely than those of a liquid or a solid. Typical gases used in detectors are argon and helium, although boron-triflouride is utilized when the detector is to be used to measure neutrons. Figure 5 shows a schematic diagram of a gas-filled chamber with a central electrode. 

Gas-filled detectors are used, for the most part, to measure alpha and beta particles, neutrons, and gamma rays. The detectors operate in the ionization, proportional, and G-M regions with an arrangement most sensitive to the type of radiation being measured. Neutron detectors utilize ionization chambers or proportional counters of appropriate design. Compensated ion chambers, BF3 counters, fission counters, and proton recoil counters are examples of neutron detectors. 

A data aquisition system based on a one dimensional, gas filled detector is shown in Fig. 31. The general philosophy of the system is to be as independant as possible from a central computer as the enormous amount of data demand an on line data analysis during the experiment. 

In the first case — to which belong the gas filled detector systems — the position of each absorbed photon has to be determined and the result has to be stored in the data acquisition system. In high counting rate experiments, these operations have to be carried out in very short times, in order to minimize dead time losses. 

The basic principle of operation of gas filled detectors, be it multiwire proportional chambers or linear devices, with a single anode wire, is the mechanism of gas amplification. This kind of detectors have — as its name implies, a filling of an... 

Although the Diethorn expression is based on a number of strong simplifications in the model for the gas amplification, the results show that it is perfectly usable for the prediction of the properties of gas filled detectors. 

The basic principles of operation which have been explained so far, are valid for one dimensional or linear detectors as well as for two-dimensional gas filled detector systems. 

Gas filled detectors, if they are well designed are not old-fashioned devices, but are highly developed pieces of equipment, which allow very accurate measurements. They can be tailored and optimized for a variety of applications, because the physicist has access to their principle of operation. In addition, they can be made large enough, such that full use can be made of the intensity of a synchrotron radiation source, with the present focal spot dimensions. The relative and even the absolute spatial resolution is very good. There is no need for a 10 micrometer resolution in most applications but more for 200 micrometer. 

The newer developments concerning gas filled detectors based on parallel electrode structures and the associated electonics are very promising concerning spatial resolution and counting rate capability. 

The parallel electrode structure with no very fine wires and with appropriate gas fillings, will turn gas filled detectors into very reliable devices. 

May be in the future, the industry will develop some kind of large CCD devices, with faster readout systems. This really would bring an innovation. In the meantime it is worth while considering that gas filled detectors already serve their purpose very well at present. 

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