Detector efficiency absolute total

Absolute total detector efficiency is the probability that a gamma emitted from a specific source will be recorded in the detector. The geometry assumed for the absolute efficiency is shown in Fig. 12.12. The intrinsic efficiency (Fig. 12.11) depends on the energy of the gamma E and the size of the detector L. The absolute total efficiency (Fig. 12.12) depends on, in addition to E and L, the radius of the detector R and the source-detector distance d. Therefore the absolute total efficiency, as defined here, is the product of intrinsic efficiency times the solid angle fraction (see also Chap. 8). 

Depending on the type of detector and measurement, the user selects the efficiency to be used. For quantitative measurements, the absolute total efficiency of the detector has to be used at some stage of the analysis of the experimental data. 

Calculated absolute total efficiencies of a Nal crystal are given in Fig. 12.15 for several source-detector distances. They have been obtained by integrating Eq. 8.20, which is repeated here (refer to Figs. 8.21 and 12.12 for notation) ... 

Figure 12.15 Calculated absolute total efficiencies of a 3 in X 3 in (76.2 mm X 76.2 mm) NalCTl) scintillator as a function of energy for different source-detector distances (from Ref. 3).

ABSOLUTE EFFICIENCY The efficiency of a detector expressed as number of entities detected compared to number emitted by the source. Can bt full-energy peak efficiency or total efficiency. 

Frequently, fluorescence measurements are expressed in relative intensity units. The word relative is used because the intensity measured is not an absolute quantity. It is a small part of the total fluorescence emission, and its magnitude is defined by the instrument slit width, detector sensitivity, monochromator efficiency, and excitation intensity. Because these are instrument-related variables, establishing an absolute intensity unit for a given concentration of a fluorophore that is valid from instrument to instrument is difficult, if not impossible. 

Dysprosium-aluminum wire has been chosen to measure the thermal-neutron spatial distribution. Dysprosium has a high cross section for thermal-neutron activation and a convenient half-life of 140 min. Thermal-neutron flux distributions will be made through the glory hole on both sides of core center and along the fine control rod when it is fully inserted. An absolute thermal-flux measurement will be made at the core center with a standard gold foil. This foil will be counted on an end-window GM counter whose efficiency for the standard gold foil has been determined from a previous standard pile irradiation. The results from the two activation detectors will yield the average thermal flux in the reactor core as described in Section II. A cadmium-ratio measurement of AGN-201 fuel can also be made in order to determine the fraction of the total fission rate due to epithermal neutrons. 

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