Electrometer, vibrating reed

Dosimetry. Ion current measurements required for absolute dosimetry were performed with a Cary 31 ionization chamber and vibrating reed electrometer. Dry nitrogen was used as filling gas for the chamber, and a W value of 34.9 e.v./ion pair was assumed for H-3 beta rays in N2 (27). Deuterium pressures in each of the reaction mixtures were great enough to ensure that less than 1% of the H-3 beta rays reached the walls of the reaction vessel (7). 

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 quadrupole mass filter (QMF) is a mass analyzer on whose operation use of an MEM is not necessarily dependent. The ion currents produced are of sufficient magnitude to be measured by means of a Faraday cage and a suitable amplifier such as a vibrating-reed electrometer. The QMF is a true M/z filter which requires no magnetic fields. Since first being proposed by Paul and Steinwedel (30), the QMF has been investigated extensively, and the principles and methods of operation are well known (see, for example, ref. 31). 

The Plasma Chromatograph (PC, registered trademark of the Franklin GNO Corp.) is also an instrument which does not depend on the use of magnetic fields (33). It should be well suited for the study of macroions because (a) the currents measured are well within the range of a Faraday cage-vibrating-reed electrometer detector system, and (b) the instrument operates at atmospheric pressure, thus making unnecessary the reduction in pressure from that of the electrospray chamber. 

For measurements of ultraviolet light from a quartz mercury arc passes through a quartz monochromator, silica lens, and window, and is focused onto the crystal at an angle of incidence of about 45°. The saturated photocurrent is collected by the surrounding metal drum to determine ip by the Fowler method (4). A vacuum thermopile measures the light intensity. Photoelectric and diffraction currents are measured by a vibrating reed electrometer. Ultra-high-vacuum techniques are employed, which result in residual pressures of less than 10-9 mm. of Hg. 

There are two practical difficulties. One is the measurement of the very small photocurrent, which may be as low as 10" amp, requiring the use of a vibrating reed electrometer or similar instrument. The second is that, for work functions above 5 eV, Vq lies in the far ultraviolet. This makes the study of some adsorptions very difficult and 6 eV is about the practical limit of such measurements. A suitable light source is the quartz mercury arc. The energy of the incident beam can be measured with a calibrated photocell, a vacuum thermopile or a radiometer. A suitable cell for adsorption studies is shown in Fig. 11. The sample being studied forms the cathode B. It can be a metal foil or a film formed by evaporation from the filament E. A wire C is fused through the glass to make contact with the... 

Fio. 2. Experimental arrangement for measuring/< in semi-insulating materials. The sample is located in a Dewar between the magnet poles. E, vibrating reed electrometer R, recorder and digital data processor F, feedback-driven shields P, potential probes M, current meter. 

The use of liquid scintillation counting in clinical laboratories and for biomedical research has increased greatly over the more than 25 years that commercial LS counters have been available. Vibrating reed electrometers and gas-filled ionization detectors for the measurement of tritium and carbon 14 respectively have been supplanted by LSC. Other commonly employed isotopes for which LSC is now the preferred method are S, Ca, Fe, and the a-emitting actinides (Mc-... 

A special Instrument system is used with the oscillator. A sensitive, uncompensated ion chamber drives a vibrating-reed electrometer which in turn feeds a voltage to a pulse converter. Output of the. converter feeds a transistorized, 200-channel time analyzer. All analyzer channels are spread across the oscillation cycle. After completion of the first cycle, subsequent cycles are stored in the corresponding equiphase channels. Over a number of cycles the coherent signals add. constructively, while the noise fills all channels uniformly. Limiting reactivities as small as 10 A k/k may be obtained. 

Putentionietry, because it is so economical of time, is usually the best choice in determining ionization constants. The apparatus described in this chaptei is based on tlic familiar potentiometer assembly commonly referred to as a pH set . If used with care, this apparatus can be made to give acceptable results. More accurate results can be obtained with a vibrating-reed electrometer, as described in Chapter 3, a piece of apparatus which is about four times more expensive. An outline of the theory of potentiometry is given in Appendix VI. 

The three-compartment source was attached to the analyzer tube of a 6-inch radius 60° sector magnetic deflection mass spectrometer. Differential pumping was used between the source and analyzer regions. The ion detector was a 14-stage electron multiplier coupled to both a vibrat-ing-reed electrometer and a pulse counter (38). The electrometer was connected to a strip-chart recorder and the counter to a printer. This arrangement allowed any range of e/m to be scanned or a given peak to be monitored. 

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