Detector Efficiency e

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... 

The quantity that gives the fraction of particles being detected is called the detector efficiency e, given by... 

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. 

This count rate can be corrected for decay since irradiation ceased (exp( - Xt )), detector efficiency (E), and branching ratio (E), which is the number of y-rays emitted per disintegration of the nucleus, in order to calculate the activity of the radionuclide, Atf... 

Figure 4.23. Absolute detector efficiency e as a function of pipe diameter Dr and distance pipe—collimator

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) ... 

Figure 4.30 Experimental values for the product of transmission T and detection efficiency e for a sector CMA as a function of the nominal kinetic energy of the analysed electrons (note the suppressed zero on the ordinate). The data have been normalized to 100% at high energies. All electrons were postaccelerated by a + 50 V potential before hitting the cone of the channeltron detector. From [KKS89].

Of course, we still have to detect the gammas and to include the solid angle of the detectors. If we have a detector of area Ad and efficiency e at a distance rd from the material in the target, we obtain the number counted... 

The counting efficiency (e) of the proportional detector is calculated as the ratio of the net count rate, in s, to the activity (A), in Bq, of this standard radionuclide solution. The net count rate is the standard s gross count rate (RG) minus the detector s background count rate (RB). The reported disintegration rate (A) is the product of the radionuclide concentration, in Bq L 1, and the amount of counted sample, in L, adjusted for the radioactive decay of the radionuclide between standardization and measurement. Equation 2A.1 is the general form of this equation. 

Step 4. Count each mounted filter with the same beta-particle detector as the samples in this experiment, Step 13, for 6,000 s. Calculate the counting efficiency, e, for 131I in Pdl2 by equation (10.1). Decay correction is for the interval between the time recorded on standard certificate and the time of counting. Record information in Data Table 10.3... 

Many laboratories have a criterion of performance based on the percent chemical yield. The recovery, for example, may have to exceed 50% to meet this criterion. The radiochemical yield is the fractional recovery of the amount of added tracer. Its measurement requires that the counter efficiency (e) is known (see Experiment 6). The counting efficiency can have been determined in a previous experiment and recorded with the detector information. 

When the counting efficiency (e) is known for a given detector and the net count rate, Rnd is determined, the absolute activity is determined using the following relationship ... 

Both T and AV are important instrumental parameters. Together with the detection efficiency e of the electron detector they determine the intensity of registered electrons, Ireg Ekin) ... 

In particular, one obtains for the area Acxp(Ekin) of a photoelectron line (see equ. (2.38) the subscript 1 is omitted, and the efficiency e of the electron detector is included) ... 

In general, relation (2.17) can be simplified by assuming that the energy distribution of electrons is independent of r and that the detector efficiency depends only on , and not on r, i.e. 

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