Flow-type ionization chamber

The instruments include an ionization chamber, the charcoal-trap technique, a flow-type ionization chamber (pulse-counting technique), a two-filter method, an electrostatic collection method and a passive integrating radon monitor. All instruments except for the passive radon monitor have been calibrated independently. Measurements were performed... 

Flow-Type Ionization Chamber PFC flow rate 1-2 /min, continuously measured, current measurement and a-pulse counting... 

Flow-Type Ionization Chamber (PFC). The Flow -Type Ionization Chamber Method (PFC) has been developed for continuously measuring radon gas in the atmospheric air. The detail of the device has been described elsewhere (Shimo, 1985). Briefly, measurements are continuously carried out by drawing air through the detector at 1.0 2.0 /min. The ionization currentdue to alpha particles from radon and its daughters is detected with a vibrating reed electrometer (VRE) in the same manner as the DSC. The sensitivity... 

The instrument was calibrated using a 1.5 liter flow-type ionization chamber The calibration factor was evaluated to be 0.318. 

Shimo, M., A Flow-Type Ionization Chamber for Measuring Radon Concentration in the Atmospheric Air, in Atmospheric Radon Familiers and Environmental Radioactivity (S. Okada, ed) pp. 37-42, Atomic Energy Society of Japan, Tokyo (1985) (in Japanese). 

Radon-222 may be transported with a carrier gas into an ionization chamber and its alpha particles counted. Short-lived isotopes in a carrier gas stream are measured this way using a flow-type ionization chamber. 

A widely used instmment for air monitoring is a type of ionization chamber called a Kaimn chamber. Surface contamination is normally detected by means of smears, which are simply disks of filter paper wiped over the suspected surface and counted in a windowless proportional-flow counter. Uptake of tritium by personnel is most effectively monitored by urinalyses normally made by Hquid scintillation counting on a routine or special basis. Environmental monitoring includes surveillance for tritium content of samples of air, rainwater, river water, and milk. 

The most common detector is the gas-flow proportional counter, although ionization chambers and G-M counters can be usefully applied in the laboratory. Several types of gas-flow proportional counters are used in modern counting laboratories. 

This concept forms the basis for the operation of gas-type ionization detectors (ionization chambers, proportional counters, and Geiger Muller counters) as illustrated in Figure 1. Ionization detectors, as the name implies, make use of the direct ionization of a sensitive volume of gas to measure radiation. A gas-filled volume is placed between two electrodes, one connected to the positive side of a d.c. power supply such as a battery and the other connected to the negative side. Thus, a potential difference is established between the two plates. A sensitive device for measuring current flow is also placed in the circuit. Under... 

Ionization smoke detectors contain a small radioactive source (Americium 241) which ionizes air in a small chamber. The ions flow to a charged plate giving a measurable current. Products of combustion in the chamber are not easily ionized and absorb the radiation and reduce the current. The low current trips the alarm circuit. The size and composition of the particles are crucial to successful detection so that some types of smoke or vapor are detected at very low (invisible) levels. 

The APCI interface uses a heated nebulizer to form a fine spray of the HPLC eluate, which is much finer than the particle beam system but similar to that formed during thermospray. A cross-flow of heated nitrogen gas is used to facilitate the evaporation of solvent from the droplets. The resulting gas-phase sample molecules are ionized by collisions with solvent ions, which are formed by a corona discharge in the atmospheric pressure chamber. Molecular ions, M+ or M , and/or protonated or de-protonated molecules can be formed. The relative abundance of each type of ion depends upon the sample itself, the HPLC solvent, and the ion source parameters. Next, ions are drawn into the mass spectrometer analyzer for measurement through a narrow opening or skimmer, which helps the vacuum pumps to maintain very low pressure inside the analyzer while the APCI source remains at atmospheric pressure. 

An ionization instrument for the analysis of gas has been developed in which the gas passes through a small chamber where it is irradiated by a small radioactive source. For a constant source of radiation, the ions produced in the gas d nd on the flow velocity of the gas and on its temperature, pressure and atomic composition. The dependence of the ionization on the atomic composition is a consequence of the different ionization potentials of the differrat types of atoms of the gas and the different probabilities for electron capture and collision. The ion current is collected on an electrode and measured. This current is a function of the gas pressure and velocity since the higher the pressure, the more ions form, while at higher velocity, the fewer ions are collected as more ions are removed by the gas prior to collection. Such ionization instruments are used in gas chromatographs and other instruments as well as in smoke detection systems (the normal radiation source is Am, usually 40 kBq), where secondary electrons condense on smoke particles, leading to lower mobility for the electrons and a decreased ion current. 

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