Ion-chamber detectors

Gas Chromatography. Gas chromatography is a well recognised method for the analysis of H—D—T mixtures. The substrate is alumina, AI2O2, coated with ferric oxide, Fe202. Neon is used as the carrier gas. Detectors are usually both thermal conductivity (caratherometer) and ion chamber detectors when tritium is involved (see Chromatography). 

Lytle, F.W., D.R. Sandstrom, E.C. Marques, J. Wong, C.L. Spiro, G.P. Huffman, and F.E. Huggins. 1984. Measurements of soft x-ray absorption spectra with fluorescence ion chamber detector. Nucl. Instr. Meth, 226 542-548. 

Lytle FW (1989) Experimental X-ray absorption spectroscopy. In Winick H, Xian D, Ye M, Huang T (eds) Applications of Synchrotron Radiation. Gordon and Breach, New York, p 135-224 Lytle FW (1999) The EXAFS family tree a personal history of the development of extended X-ray absorption fine structure. J Synchrotron Rad 6 123-134 Lytle FW, Greegor RB, Sandstrom DR, Marques DR, Wong J, Spiro CL, Huffman GP, Huggins FE (1984) Measurement of soft X-ray absorption with a fluorescence ion chamber detector. Nucl Instrumen Methods 226 542-548... 

Ion-chamber detectors are very useful because gaseous combustion products that form even before there is any smoke can set them off. But this also means that shower steam can trigger them, and that can be a nuisance. However, the protection the detector offers eclipses such minor annoyances. Of course, that protection is only available if the detector is working properly. Remember that pushing the test button on the unit will only... 

Pb(C2H5)4 sorbed from air onto atmospheric particulates decomposed in 10 h at 90 partially to inorganic lead compounds [81]. A thermoanalytical investigation of Pb(C2H5)4-laden activated carbon showed that adsorbed Pb(C2Hg)4 and the activated substrate decompose at or above 60 C [86]. Pyrolysis of Pb(C2Hs)4 was used for analysis as air contaminant in sensitizing an ion chamber detector [56]. 

Instrumentation. Traditional methods of alpha and beta spectrometry instrumentation have changed little over the past decade. Alpha spectrometric methods typically rely on semi-conductor or lithium-drifted silicon detectors (Si(Li)), or more historically gridded ion chambers, and these detection systems are still widely used in various types of uranium-series nuclide measurement for health, environmental, and... 

The discharge compartment is mechanically separated from the ionization chamber by an optically transparent window made of setal fluoride. The effluent from the column passes through the themostated ionization chamber and between two electrodes, positioned at opposite ends of the chamber. Detectors with ionization chamber volumes of 40 and 175 microliters are available for use with capillary columns and of 175 and 225 microliters for packed columns. An electric field is applied between the electrodes to collect the ions formed (or electrons, if preferred) and the current amplified by a precision electrometer. It has been shown that careful thermostating of the detector is required to reduce baseline drift [107,109]. 

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. 

Percent compensation of a compensated ion chamber gives the percentage of the gamma rays which are canceled out. Percent compensation may be calculated based on measured current, when the detector is exposed to gamma rays only as given in Equation 6-9. 

Several means are employed to detect X-rays with ion chambers and scintillation detectors sufficient for use in the adsorption and reflection methods where only the intensity of the X-ray beam is of interest. However,... 

Figure 6.19 Catalytic in situ reactor made of a quartz capillary, suitable for use at synchrotrons for the collection of EXAFS an XRD data. The scheme of the synchrotron beamline shows the positions of the mono-chromator, the ion chambers which measure the intensity of the X-rays before and after the sample, and the position-sensitive X-ray detector which records the XRD diffractogram (adapted from Clausen [44]).

The monochromatic X-ray was obtained by silicon (111) channel cut double crystal using white X-ray (at Beam Line 4A (PF)). The ion chambers were set at the both side of the photoacoustic cell, in order to compare the sp trum of photoacoustic X-ray absorption spectroscopy (PAXAS) with usual absorption spectrum, simultaneously. The chopper at chopping frequency of 10 Hz was t at the up-stream of these detectors. Copper foil (5 pm thick) was used as a sample. 

This value corresponds to an absorbed energy of approximately 8.8 mJ/kg using the effective ionization energy of 34 eV per ion pair in air. The roentgen is most often used to describe the intensity of a photon source such as a medical X-ray machine or other irradiator. The exposure should be measured at some distance from the soiuce so that the radiation field is uniform compared to the dimensions of the detector. The detector is usually an ion chamber filled with dry air that is sensitive to pico-coulombs of charge. 

Figure 18.3 Schematic diagram of tin ion chamber that drifts the ionization perpendicular to the particle s path is shown. In this case the anode is segmented and the relative rate of ionization along the path can be determined. The device also contains a Frisch grid between the anode and chamber to improve the pulse-shape response of the device, (c) The schematic version of a detector that drifts the ionization along the particle s path, called a Bragg counter, is shown. The time distribution of the output signal will contain information on the relative rate of ionization all along the particle s path.

When the energy of the charged particle beam is too large to easily stop the beam in a Faraday cup, the beam intensity is frequently monitored by a secondary ionization chamber. These ion chambers have thin entrance and exit windows and measure the differential energy loss when the beam traverses them. They must be calibrated to give absolute beam intensities. If the charged particle beam intensity is very low (<106 particles/s), then individual particles can be counted in a plastic scintillator detector mounted on a photomultiplier tube. 

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