Detector efficiency relative

The quantitative evaluation of relative intensities for selected photo- or Auger processes requires information about both the relative kinetic energy dependence of the analyser transmission T (see Fig. 4.15) and the accompanying detection efficiency e of the electron detector. The relative magnitude for the desired product Te can be determined directly if, for example, non-coincident electron and ion spectrometry are combined with helium as target gas, the Is photoline is recorded as a function of the photon energy and yields the dispersion corrected area AD (electron) see equ. (2.39) ... 

Another commonly-used normalisation procedure is to use the relative flow technique. In this method the elastic differential cross section for a particular species may be obtained by comparing the scattered intensity under the same conditions with that from another target with a known cross section. It is important to ensure, for both the gas under study and the reference gas, that the electron flux density and distribution, the detector efficiency, and the target beam flux distribution are the same for both gases during the measurement. 

In both scintillator and gas detectors, the absorption of radiation causes excitation and ionization however with the scintillation process, the absorbed energy produces a flash of light, rather than a pulse of current. The principal types of scintillation detectors found in the clinical chemistry laboratory are the sodium iodide crystal scintillation detector and the organic liquid scintillation detector. Because of the crystal detector s relative ease of operation and economy of sample preparation, most clinical laboratory procedures have been developed to measure nucfides, such as which can be counted efficiently in a crystal detector. A liquid scintillation detector is used to measure pure (3-emitters, such as tritium or C. 

Radioactive tracer techniques have long been used to study particle motion in solids fluidization systems. The advantage of this technique is that the flow field is not disturbed by the measurement facility and, therefore, the measurement of the motion of the tracers represents the actual movement of particles in the system. The tracer particles are usually made of gamma-emitting radioisotopes, and their gamma radiation is measured directly by scintillation detectors. Factors that affect gamma radiation measurement were identified as the characteristics of the radiation source, interactions of gamma rays with matter, the tracer s position relative to the detector, detector efficiency, and dead time of the measurement system. 

Thus, even though the Ge detector is only 10 percent efficient, relative to the NaI(Tl) crystal, it produces a peak that is 3.5 times higher. 

With the exception of a and all of these factors, especially the intrinsic efficiency of a detector, which is determined by the detection principle and the size of the sensitive volume of the detector, depend on the type and energy of radiation. Their relative contributions to the counting yield differ widely from detector to detector. Decay schemes of the nuclides to be measured, intrinsic detector efficiency, geometry and radiation absorption effects are of primary importance in selecting a detector for a certain application. Some of the secondary factors may play no role in certain detectors and/or applications. In principle, any factor in eqn. 8 that contributes significantly can be used to increase the counting yield. 

End-window proportional counters with thin windows that separate sample from detector have the alpha-particle counting efficiency shown in Table 8.1 for thin samples on planchets. The lesser counter efficiency relative to the internal detector is due to less than 27t geometry and attenuation in sample, air space, and window. 

The lithium drifted detectors provided greater resolution but at a higher cost and lesser counting efficiency relative to the Nal(Tl) detectors. Additionally, the Ge(Li) detector must be kept at liquid nitrogen temperature at all times to prevent lithium ions from drifting in the germanium to destroy the detector. 

A standard method is described in IEEE standard test procedures (IEEE 1996) to define the relative detection efficiency for a coaxial detector. The relative efficiency 6r for a coaxial detector is defined as follows ... 

The parameter r LDWJUb predicts the extent of conversion efficiency. For r 0.33, the diffusion layer touches the opposite channel wall. For r approximately greater than 2, the cell attains 100% yield. Basically, r describes an aspect ratio based on transit time through the detector cell relative to diffusion time across the channel height. 

The above fundamental parameter equation relates the intensity of one element to the concentration of all elements present in the sample. A set of such equations can be written, one for each element to be determined. This set of equations can only be solved in an iterative way, making the method computationally complex. Moreover, an accurate knowledge of the shape of the excitation spectrum Io E)dE, of the detector efficiency e and of the fundamental parameters //, r, w and p is required. The fundamental parameter method is of interest because it allows for semi-quantitative (5—10% deviation) analysis of completely unknown samples and is therefore of use in explorative phases of investigations. Several computer programs are available that allow one to perform the necessary calculations at various levels of sophistication. As an example, in Tab. 11.9, the relative standard deviation between certified and calculated concentration of the constituents of a series of tool steels are listed. 

A detailed description of a commercially available LC chiral detector will be given in the chapter 7. However, some general comments on the properties of chiral detectors would be appropriate here. Contemporary, chiral detectors are relatively insensitive and, consequently, there are no GC chiral detectors commercially available at this time. Capillary columns will only function with very small charges and these types of column must be employed for the great majority of chiral separations, in order to provide the necessary efficiency. Unfortunately, the sensitivity of chiral sensing systems, investigated so far, have been inadequate for use with GC capillary columns. In contrast, after considerable research and development, the sensitivity of LC chiral detectors has been improved to a level where (although still relatively insensitive) they can often be used satisfactorily with contemporary small particle LC chiral columns. 

In many cases, the fiill detector efficiency can be factorized into intrinsic and geometric efficiencies. The intrinsic efficiency is the ratio of the number of recorded pulsestothe number of gamma rays incident on the detector surface, which depends on the interactions between the gamma photons and the material of the detector, as discussed above, while the geometric efficiency equals the fraction of the gamma rays reaching the detector relative to the emitted ones. 

Note 2 The mixed Th/ Th planchet is worthless after the decay of Th. A useful standardization can be made with a planchet with 60dpmU electrodeposited on it (evaporate a weighed aliquot in a small Teflon beaker and follow electrodeposition procedure of Th Section 13.7.7). After ingrowth of Th to secular equilibrium with (several months), the planchet can be used for a check on the relative efficiencies of beta and alpha counters. Alpha detector efficiency determined this way for should also be applicable to but an independent calibration of the °Th spike is still required. 

Detector type Relative efficiency (%) Threshold fast neutron dose (cm )... 

Relative conversion efficiency (relative to NaI(Te)), i.e. net detector output using a bialkali photomultiplier tube (PMT). 

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