Calibration of detectors

The calibration source consists of a 20 keV electron gun and a series of metal targets (Mn, Cr, V, Ti) located on the opposite port to the spectrometer as indicated in Fig. 1. Calibration spectra are collected for a range of Ka and K/3 characteristic wavelengths (1.9A-2.8A) about the helium-like resonances of vanadium. Ka and Ka2 are well resolved in our system and so the Ka doublet provides two reference wavelengths at one detector location. This gives an absolute calibration of detector scale [17,18],... 

The International Atomic Energy Agency organized a series of interlaboratory comparisons for calibration purposes. Those completed so far include two seawater, one seaweed Fucus vesiculosus), and one sediment sample. These materials were contaminated in nuclear waste disposal situations and, in consequence, contain transuranic elements in concentrations much higher than those found in samples contaminated by global fallout of nuclear weapons testing debris. Nevertheless, the data speak directly to questions of calibration of detectors and yield... 

This appendix contains evaluated and recommended data on a selected set of radionuclides suitable for use in the energy and efficiency calibration of detectors. The data in the first edition of this book were taken from X-Ray and Gamma-Ray Standards for Detector Calibration, published by the International Atomic Energy Agency as IAEA TECDOC-619. Since that time, the data have been re-evaluated and extended within the international Decay Date Evaluation Project (DDEP). After much delay, the updated data were published by the IAEA as XGAMMA (X-ray and Gamma-ray Decay Data Standards for Detector Calibration and Other Applications) in late spring, 2007. 

Fig. 1 shows the block diagram of the vibrometer, in which the most sensible to small phase variations interferometric scheme is employed. It consists of the microwave and the display units. The display unit consists of the power supply 1, controller 2 of the phase modulator 3, microprocessor unit 9 and low-frequency amplifier 10. The microwave unit contains the electromechanical phase modulator 3, a solid-state microwave oscillator 4, an attenuator 5, a bidirectional coupler 6, a horn antenna 7 and a microwave detector 11. The horn antenna is used for transmitting the microwave and receiving the reflected signal, which is mixed with the reference signal in the bidirectional coupler. In the reference channel the electromechanical phase modulator is used to provide automatic calibration of the instrument. To adjust the antenna beam to the object under test, the microwave unit is placed on the platform which can be shifted in vertical and horizontal planes. 

Table 15. Decay Data for Radionuclides Useful for the Energy and Efficiency Calibration of 7-Ray Detectors...

Calibrate the detector tube pump for proper volume measurement at least quarterly. Simply connect the pump directly to the bubble meter with a detector mbe in-line. Use a detector mbe and pump from the same manufacturer. Wet the inside of the 100 cc bubble meter with soap solution. For volume calibration, experiment to get the soap bubble even with the zero ml mark of the buret. For piston-type pumps, pull the pump handle all the way out (full pump stroke) and note where the soap bubble stops for bellows-type pumps, compress the bellows fully for automatic pumps, program the pump to take a full pump stroke. 

This technique is invasive however, the particle can be designed to be neutrally buoyant so that it well represents the flow of the phase of interest. An array of detectors is positioned around the reactor vessel. Calibration must be performed by positioning the particle in the vessel at a number of known locations and recording each of the detector counts. During actual measurements, the y-ray emissions from the particle are monitored over many hours as it moves freely in the system maintained at steady state. Least-squares regression methods can be applied to evaluate the temporal position of the particle and thus velocity field [13, 14]. This technique offers modest spatial resolutions of 2-5 mm and sampling frequencies up to 25 Hz. 

Figure 3. Calibration curves of detector at wavelengths (O) 254 run . 32X ([2) 280 run,. 16X and (l ) 350 nm,. 16X (test solute sodium dichromate)...

Compared with the sensors for atoms and radicals, the calibration of EEP sensors is also somewhat specific. To calibrate detectors of atomic particles, it will be generally enough to determine (on the basis of sensor measurements) one of the literature-known constants, say, tiie energy of parent gas dissociation on a hot Hlament. For the detection of EEPs when nonselective excitation of gas is taking place, in order to calibrate a sensor use should be made of some other selective methods detecting EEPs. The calibration method may be optical spectroscopy, chemical and optic titration, emission measurements, etc. 

Standards are used for a number of purposes. An external standard contains a mixture of substances typically observed in the sample. Knowledge of the concentration of the standard substances allows calibration of the detector to compensate for run-to-run or day-to-day variability. External standards should not be subjected to hydrolysis or other sample processing steps, except as necessary for detection, since this would add other sources... 

The determination of the relationship between detector response and the sample concentration is termed the calibration of the method. There are two types of methods in use for the quantitative analysis of a sample, i.e., the external standard and the internal standard method. An external standard method is a direct comparison of the detector response of a pure compound (standard) to a sample.2 The calibration of the method is performed by preparing standards of varying concentration and analyzing them by a developed method. Method 1 (below) was developed for toluene, and standards of varying concentration were prepared and analyzed. The results obtained are summarized in Table 2 see Figure 3. 

Figure 4 Calibration of external and internal standard method. Chromatographic conditions — column 30 cm x 3.9 mm p-Bondapak C18 (10-pm particle size) mobile phase water acetonitrile (50 50) flow rate 1.5 ml/min column temperature ambient detector wavelength 254 nm. (A) External standard method, (B) internal standard method.

Calibration of an internal standard method is done by preparing standard samples of varying concentration. The same amount of IS is added to each, and the standard samples are analyzed using a developed method. The detector response, area or height, of each standard is determined, and a ratio is calculated. The graph of concentration vs. area ratio is plotted. The method is considered linear if the correlation coefficient is 0.99 or better. The response factor RF is calculated as... 

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