Detector efficiency

In research environments where the configuration and activity level of a sample can be made to conform to the desires of the experimenter, it is now possible to measure the energies of many y-rays to 0.01 keV and their emission rates to an uncertainty of about 0.5%. As the measurement conditions vary from the optimum, the uncertainty of the measured value increases. In most cases where the counting rate is high enough to allow collection of sufficient counts in the spectmm, the y-ray energies can stih be deterrnined to about 0.5 keV. If the configuration of the sample is not one for which the detector efficiency has been direcdy measured, however, the uncertainty in the y-ray emission rate may increase to 5 or 10%. 

Alpha counting is done with an internal proportional counter or a scintiUation counter. Beta counting is carried out with an internal or external proportional gas-flow chamber or an end-window Geiger-MueUer tube. The operating principles and descriptions of various counting instmments are available, as are techniques for determining various radioelements in aqueous solution (20,44). A laboratory manual of radiochemical procedures has been compiled for analysis of specific radionucHdes in drinking water (45). Detector efficiency should be deterrnined with commercially available sources of known activity. 

The detected yield is a function of the concentration of the element being profiled, the resonance cross section, the detector efficiency, and dE/dx. To be specific. 

This is a method which is very attractive in principle and which has been applied to yield approximate barriers for a number of molecules. There are, however, difficulties in its use. In the first place, it is not easy to measure the intensities of microwave lines with accuracy. There are unsolved problems of saturation, reflections in the wave guide, and variation of detector efficiency with frequency which are presumably reponsible for the fact that measurements made with ordinary wave guide spectrometers are not very reproducible. In addition, both the spectral lines may be split into components by tunnelling from one potential minimum to another and this splitting, even though it is not resolved, can alter the apparent intensity. Furthermore, it is often difficult to find pairs of lines such that neither is obscured by Stark lobes from the other. 

Principles and Characteristics Problems connected with sample preparation, ionisation and detector efficiency can lead to errors in the quantitation of mass averages and MWD in the case of ESI-MS and MALDI-MS. Coupling of SEC with MS makes it possible to overcome these difficulties. SEC-MS has developed since the early 1990s. Two methods are currently outstanding on-line SEC-ESI-MS (QMS or FTMS) and semi on-line SEC-MALDI-ToFMS [709],... 

The diffractometer has gradually evolved in terms of maximum power of sealed X-ray tubes, rotating anodes, new X-ray optics, better detector efficiency, position-sensitive detection and, lately, real-time multiple-strip (RTMS) fast X-ray detection, which replaces a single detector by an integrated array of parallel detectors to provide an up to 100-fold increase in efficiency compared with traditional detectors without compromise on resolution. Time-resolved powder diffraction is... 

I(q) is the intensity at wave vector q, (bjjr-bp) is a contrast factor arising from the difference in scattering lengths of deuterated and protonated species, M is molecular weight of the deuterated polymer, c is concentration in gm/ml, S(q) is a particle scattering factor, and A contains machine constants, detector efficiency, and other fixed quantities. For the purpose of the current study, S(q) is the quantity of significance, and it is given by... 

The degree of activation of the sample is measured by post-irradiation spectroscopy, usually performed with high-purity semiconductors. The time-resolved intensity measurements of one of the several spectral lines enables to get the half-life of the radioactive element and the total number of nuclear reactions occurred. In fact, the intensity of a given spectral line associated with the decay of the radioactive elements decreases with time as Aft) = Aoexp[—t/r], where Aq indicates the initial number of nuclei (at t = 0) and r is the decay time constant related to the element half-life (r = In2/ /2), which can be measured. Integrating this relation from t = 0 to the total acquisition time, and weighting it with the detector efficiency and natural abundance lines, the total number of reactions N can be derived. Then, if one compares this number with the value obtained from the convolution of... 

The hydrocarbon values are not corrected for the small differences in detector efficiencies.) The exiting gases are analyzed for CO, CO2, and CH with a gas partitioner equipped with a thermistor detector. The peak areas obtained from the gas partitioner are converted to weight percentages by using the appropriate sensitivity factors (12). 

The equilibrium constants can be approximated by ratios of ion currents in some instances otherwise, the currents are converted to partial pressures by comparison with the evaporation of known amounts of a standard material. Various geometric corrections (K) such as the solid angle subtended by the sample at the orifice, the Clausing factor for orifice geometry, molecular cross-section (o-), which control ionization efficiency, and detector efficiency are included in the general relationship... 

Figure 7.6. Detector efficiency for photodiodes. Spectra for (A) a silicon photodiode and (B) a PIN silicon photodiode are shown. The peak wavelength response of both detectors is at 960 nm,...

Figure 9. Detector efficiency at the 1S7Cs energy for Ge(Li) detectors of...

Figure 10. Detector efficiency as a function of gamma-ray energy for an 8-cm.3 (Ge(Li)) detector (samples in aluminum cans). The efficiency of the 18-cm.s detector increases in proportion to the surface area...

Counting rates in a detection system are usually given in counts per second (cps), counts per minute (cpm), and so on, and differ from the disintegration rates by a factor representing the detector efficiency, e. Thus... 

Compute the amount of a radionuclide necessary to perform an experiment with a sample count rate of 1000 cpm, a detector efficiency of 33%, a sample aliquot for counting consisting of 10% of the total isolated sample and where the percent incorporation of the nuclide into the total isolated sample was 0.5%. 

Isotope X, with a half-life of 5 d, is to be used in an experiment that includes the following factors (a) sample count rate of 100 cpm, (b) detector efficiency of 10%, (c) assume the sample with the lowest count rate will represent a 0.5% incorporation, and (d) assume all samples will represent only 5% of the total isotope administered. What amount of X must be used ... 

Detector Efficiency If 100 y rays strike a detector, exactly how many will be detected Each detector discussed here will be evaluated using these basic criteria. 

The Q values in these tensors represent the Stokes parameters for the spin sensitivity of the detector in its x", y", z" frame. For example, Qx- describes the detector efficiency for measuring spin projections along +x" and —x", respectively (for the definition of the spin polarization vector see Section 9.2.1). 

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