Instrumentation Counter

The protection follows three stages prevoition, supervision, and after-control. Preventive measures include use of fume hoods, or-boxes, radiation shielding, tongs, etc., as discussed above. The supervision stage involves the use of radiation instrum ts to monitor the radiation level (see Ch. 8). Small TLD, film or pocket pen dosimeters are used for individual monitoring ( 7.9). For spills and contamination of hands, shoes, etc., special contamination instruments (counters) are used which are more sraisitive than the monitoring dose instrumrats. 

Geiger counter an instrument for counting radioactive particles based on their ability to ionize an inert gas such as Ar. (p. 643)... 

For either the in-line or hybrid analyzers, the ions injected into the TOF section must all begin their flight down the TOF tube at the same instant if arrival times of ions at a detector are to be used to measure m/z values (see Chapter 26, TOF Ion Optics ). For the hybrid TOF instruments, the ion detector is usually a microchannel plate ion counter (see Chapter 30, Comparison of Multipoint Collectors (Detectors) of Ions Arrays and MicroChannel Plates ). 

Instruments operating during discharges alone are basically surge counters and can only indicate the number of discharges. They provide no information on the condition of the arrester. 

The electrical aerosol analyzer and the optical counter are used to measure particle size distributions. Describe the size range and resolution characteristics of each of these instruments. 

Oatley and a succession of brilliant students, collaborating with others at the Cavendish Laboratory, by degrees developed an effective instrument a key component was an efficient plastic scintillation counter for the image-forming... 

Optical particle counter An optical-electronic instrument for measuring the numbei" of airborne particles in different size ranges. 

At frequencies higher than this, a solid-state counter must be used. This is based on a stable oscillator and, in effect, counts the pulses generated during one cycle of the supply frequency. The range and accuracy of the instrument depends on the master oscillator frequency, but units capable of use over the whole range up to 600 MHz... 

A liquid scintillation counter. This instrument is used to detect radiation and measure disintegrations per minute quickly and accurately. 

Commercial polarographs are also available in which the voltage scan is carried out automatically while a chart recorder plots the current-voltage curve. A counter-current control is incorporated which applies a small opposing current to the cell which can be adjusted to compensate for the residual current this leads to polarograms which are better defined. Most of these instruments also incorporate circuits which permit the performance of alternative, more sensitive types of polarography as discussed in Section 16.9... 

The performance of the Micromerograph has been of interest ever since its introduction because of its potential for a much needed improvement in the analyses of the important sub-sieve sized ingredients of Ordnance. It has been evaluated relative to several other instruments Coulter Counter... 

J.G. Day D.R. Dillehay, ibid, 277-285 3.0) D.E. Middlebrooks, S.M. Kaye, D.J. Edel-man G. Weingarten, Preliminary Evaluation of the Coulter Counter Particle Size Instrument , PATM 1054(1963) 31) J.A. Freitag, Four-... 

Uniformly labeled C-8-D with a specific activity of 2.99 juc/mg was administered orally to pregnant females at 2 /xg/kg/day from 6-15 days of gestation. Three females were sacrificed on alternate days during days 6-20 of pregnancy. Triplicate samples of fetus, placenta, blood, brain, abdominal fat, and sartorius muscle were procured from each female. The samples were dissolved in 1 ml of Soluene (Packard Instruments) to which 15 ml of Aquasol were added. Each sample vial was counted for 30 min in a Nuclear Chicago Mark I liquid scintillation counter. 

If only one counter can be purchased, then a gamma counter is the instrument of choice since most assays are now performed with gamma emitting isotopes. Table I lists the isotopes in common usage for competitive protein binding assays. 

Perhaps the most useful method for determining particle distributions is that of electrical conductivity, the most widely used instrument is the Coulter Counter (named after the Inventors), although there are now other similar instruments on the market. Originally, this instrument was designed to measure blood corpuscles which are 2-8 p in size. It has proven to be very... 

The potentiostat has a three-electrode system a reference electrode, generally a saturated calomel electrode (SCE) a platinum counter, or amdliary, electrode through which current flows to complete the circuit and a working electrode that is a sample of interest (Fig. 25-10). The potentiostat is an instrument that allows control of the potential, either holding constant at a given potential, stepping from potential to potential, or changing the potential anodically or cathodically at some linear rate. 

Solid-state detectors based on silicon- or germanium-diodes possess better resolution than gas counters, particularly when cooled with liquid nitrogen, but they allow only very low count rates. PIN diodes have also recently become available and have been developed for the instruments used in the examination of Martian soils (Sects. 3.3 and 8.3). A very recent development is the so-called silicon-drift detector (SDD), which has very high energy resolution (up to ca. 130 eV) and large sensitive detection area (up to ca. 1 cm ). The SNR is improved by an order of magnitude compared to Si-PIN detectors. Silicon drift detectors may also be used in X-ray florescence spectroscopy, even in direct combination with Mossbauer spectroscopy (see Sects. 3.3 and 8.3). 

Measurement of specific activity. The half-life of a nuclide can be readily calculated if both the number of atoms and their rate of decay can be measured, i.e., if the activity A and the number of atoms of P can be measured, then X is known from A = XP. As instrumentation for both atom counting and decay counting has improved in recent decades, this approach has become the dominant method of assessing half-lives. Potential problems with this technique include the accurate and precise calibration of decay-counter efficiency and ensuring sufficient purity of the nuclide of interest. This technique provides the presently used half-lives for many nuclides, including those for the parents of the three decay chains, U, U (Jaffey et al. 1971), and Th. 

The basic function of the spectrometer is to separate the polychromatic beam of radiation coming from the specimen in order that the intensities of each individual characteristic line can be measured. In principle, the wide variety of instruments (WDXRF and EDXRF types) differ only in the type of source used for excitation, the number of elements which they are able to measure at one time and the speed of data collection. Detectors commonly employed in X-ray spectrometers are usually either a gas-flow proportional counter for heavier elements/soft X-rays (useful range E < 6keV 1.5-50 A), a scintillation counter for lighter elements/hard X-rays (E > 6keV 0.2-2 A) or a solid-state detector (0.5-8 A). 

Table 8.40 compares the main characteristics of WDXRF and EDXRF. Multidispersive XRF combines the benefits of the WDXRF technique for routine elemental analysis with the complete flexibility offered by EDXRF for nonroutine analysis. Clearly, modem XRF instrumentation is rather varied, ranging from simple benchtop EDXRF equipped with a low-power X-ray tube and high-resolution proportional counter for some key elements, to 4 kW simultaneous multichannel spectrometers with 28 fixed element channels for... 

---