Radiometric energy measurement

There is a wide range of applications for methods of analysis that are based upon the energies and intensities of the radiations emitted by radioactive nuclides. These techniques sometimes are temied radiometric methods of analysis. The methods are not restricted to the determination of substances initially radioactive, since there is wide use of methods involving the irradiation of stable, nuclides to produce radioactive ones, followed by measurement of their radiations, horn which the composition of the original stable substance can be inferred This method is radioactivation analysis. Another method for the use of measurements of radioactivity in the analysis of stable substances is that of tracer techniques, that is, by the addition to them of radioactive nuclides, which can then be used to follow the course of various reactions or processes. There are various ways of introducing the radioactive nuclides, which are discussed later in this entry. 

All methods of radiometric analysis involve, of course, the use. of various radiation detection devices, The devices available for measuring radioactivity will vary with the types of radiations emitted by the radioisotope and the kinds of radioactive material. Ionization chambers are used for gases Geiger-Miiller and proportional counters for solids liquid scintillation counters for liquids and solutions and solid crystal or semi-conductor detector scintillation counters for liquids and solids emitting high-energy radiations. Each device can be adopted to detect and measure radioactive material in another state, e.g., solids can be assayed in an ionization chamber. The radiations interact with the detector to produce a signal,... 

A tracer usually is a solution of a standardized radionuclide that is an isotope of the analyte radionuclide. With the identical chemical behavior of tracer and analyte, the yield of the tracer, determined radiometrically, represents the yield of the analyte. In this respect, the radioactive tracer has the same function as the stable carrier. Furthermore, for alpha particles of the usual 4-10 MeV energy in a thin source, the ratio of net count rate to activity is the same for the tracer and the analyte, so that the analyte activity is directly calculated from the activity of the tracer and ratio of the net count rates at the peaks of the analyte relative to the tracer, measured with an alpha-particle spectrometer. 

Source represents the emission of radiant energy, which may be per unit time or area or both. In the cgs system of units, radiant energy is measured in ergs and in the inks system it is measured in joules. Other radiometric units evolve as listed in Table 16.1. 

Radiometric quantities are important to describe and measure UV and VUV radiation. They are usually subdivided into energetic, spectral and photonic terms. Energetic terms (Tab. 3-9) are based on the energy of the radiation and they refer to all relevant wavelengths. Eor each of these terms a spectral derivative can be defined (Bolton, 1999) which is correlated with a specific wavelength X. Eor example, the extraterrestrial solar spectrum incident on the upper atmosphere is represented by the mean spectral irradiance Eq in W m nm over a defined wavelength interval AX in nm (CIE, 1989). Further, each of the spectral units can easily be transferred to photon-based units, which themselves are related to radio-metric units (cf Braun et al., 1991). 

Radiometry The measurement of quantities associated with radiant energy. The radiometric unit of intensity is irradiance. 

Using the above assumption, Rais [115] divided into components the radiometrically measured distribution coefficients and energies of transfer of various salts from water saturated with nitrobenzene to nitrobenzene saturated with water. 

The word radiometry describes the detection and measurement of radiated electromagnetic energy, and is also used to describe the prediction and calculation of the power transferred by radiation from one object or surface to another. The concepts of radiometry are so similar to those of photometry (related to vision and detection by the human eye) and to the transfer of photons that it is convenient to discuss all three together. In fact, we rarely need to distinguish between the three disciplines, and we will use the word radiometry to cover all three. The radiometric calculations described in this chapter are a necessary part of the characterization of detectors and the prediction of signal and noise levels. 

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