Gamma-rays overview

The ratio of the resistivity (R ) in sediment to the resistivity (R. ) in pore water defines the formation (resistivity) factor (F). (a) and (m) are constants which characterize the sediment composition. As Archie (1942) assumed that (m) indicates the consolidation of the sediment it is also called cementation exponent (cf. Sect. 3.2.2). Several authors derived different values for (a) and (m). For an overview please refer to Schon (1996). In marine sediments often Boyce s (1968) values (a = 1.3, m = 1.45), determined by studies on diatomaceous, silty to sandy arctic sediments, are applied. Nevertheless, these values can only be rough estimates. For absolutely correct porosities both constants must be calibrated by an additional porosity measurement, either on discrete samples or by gamma ray attenuation. Such calibrations are strictly only valid for that specific data set but, with little loss of accuracy, can be transferred to regional environments with similar sediment compositions. Wet bulk densities can then be calculated using equation 2.3 and assuming a grain density (cf. also section 3.2.2). 

FIGURE 32-6 Overview of the neutron activation process. The incident neutron is captured by the target nucleus to produce an excited compound nucleus, which de-excites with emission of a prompt gamma ray. The radioactive nucleus formed decays by emitting a beta particle. If an excited product nucleus is formed, a delayed gamma ray can be emitted. If decay is directly to the ground state of the product nucleus, no gamma ray is emitted. 

See also Activation Anaiysis Neutron Activation. Extraction Solvent Extraction Principles. Geochemistry Sediment. Ion Exchange Overview. Mass Spectrometry Ovenriew. Radiochemical Methods Gamma-Ray Spectrometry. Sample Dissolution for Elemental Analysis Dry Ashing. Spectrophotometry Overview. X-Ray Fluorescence and Emission X-Ray Fluorescence Theory. 

Meat Products. Pharmaceutical Analysis Overview. Radiochemical Methods Overview Natural and Artificial Radioactivity Radionuclide Monitoring Radon Radiotracers Gamma-Ray Spectrometry. Water Analysis Freshwater Seawater-Organic Compounds Seawater-Inorganic Compounds. 

Activation methods are based on the measurement of the radioactivity or radiation produced in samples when they are irradiated with neutrons or charged particles, such as hydrogen, deuterium, or helium ions. An overview of the most common type of neutron activation is shown in Figure 32-6. Here, a neutron is captured by the target nucleus to form an excited compound nucleus. The compound nucleus de-excites almost instantaneously by emission of one or more characteristic prompt gamma rays. In many cases a new radioactive nucleus is formed, which can undergo /3 decay to an exited product nucleus with the emission of another characteristic delayed gamma ray. 

In the first section a brief overview of the properties of Lanthanum Halides crystals is presented. In section 2 the performances of LaBrsiCe and LaClsiCe gamma-rays deteetors are discussed in fom subsections on internal activity, radiation hardness, particles identifieation time and energy resolution. Section 3 presents some recent results on the use of such detector in a position sensitive mode. 

The uranium content in soil can be determined directly by some analytical methods that are mainly based on nuclear techniques (variations of neutron activation analysis, gamma spectrometry, x-ray fluorescence, or laser-ablation ICPMS), but the common, popular, and more accurate methods require digestion and dissolution of the entire soil sample or at least rely on leaching the uranium out of the sample matrix. In principle, the methods used for assaying uranium in minerals (see Chapter 2) are also suitable for soil characterization, but uranium is usually present in the latter only as a low-level impurity, usually below 100 pg U g. We shall first overview the procedures deployed for the treatment of soil samples prior to analysis and refer to the analytical devices used for the measuranent of the uranium content and isotopic composition in these studies. 

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