Gamma cross-section

AMPX system to produce coupled neutron-gamma cross-section libraries. 

In situ measurement of the concentration of radioactive tracers in the different phases requires that the phases are separated and arranged according to density difference over the measurement cross section in a horizontal pipe. In general, the measurements are performed with two spectral gamma radiation detectors placed on top and bottom of the pipe respectively. 

Figure 4-270. Cross-section of an MWD focused gamma ray tool. (Courtesy SPWLA [112]. ...

Mossbauer spectroscopy involves the measurement of minute frequency shifts in the resonant gamma-ray absorption cross-section of a target nucleus (most commonly Fe occasionally Sn, Au, and a few others) embedded in a solid material. Because Mossbauer spectroscopy directly probes the chemical properties of the target nucleus, it is ideally suited to studies of complex materials and Fe-poor solid solutions. Mossbauer studies are commonly used to infer properties like oxidation states and coordination number at the site occupied by the target atom (Flawthome 1988). Mossbauer-based fractionation models are based on an extension of Equations (4) and (5) (Bigeleisen and Mayer 1947), which relate a to either sums of squares of vibrational frequencies or a sum of force constants. In the Polyakov (1997)... 

Self-powered neutron detectors (SPNDs) use a material such as cadmium that has a high cross section for low-energy neutrons and produces copious gammas or... 

Soft white, ductile metal high-purity metal is very ductile at ordinary temperatures occurs in three allotropic forms (i) body-centered cubic form, alpha iron stable up to 910°C, (ii) face-centered cubic form, gamma iron occurring between 910 to 1,390°C, and (iii) body-centered delta iron allotrope forming above 1,390°C. Density 7.873 g/cm at 20°C melting point 1,538°C vaporizes at 2,861°C hardness (Brinell) 60 electrical resistivity 4.71 microhm-cm at 0°C tensile strength 30,000 psi Poisson s ratio 0.29 modulus of elasticity 28.5 X 10 psi thermal neutron absorption cross-section 2.62 bams velocity of sound 5,130 m/s at 20°C. 

In some cases, thermal neutrons can also be used to measure the absolute abundances of other elements. Transforming the neutron spectrum into elemental abundances can be quite involved. For example, to determine the titanium abundances in lunar spectra, Elphic et at. (2002) first had to obtain FeO estimates from Clementine spectral reflectances and Th abundances from gamma-ray data, and then estimate the abundances of the rare earth elements gadolinium and samarium from their correlations with thorium. They then estimated the absorption of neutrons by major elements using the FeO data and further absorption effects by gadolinium and samarium, which have particularly large neutron cross-sections. After making these corrections, the residual neutron absorptions were inferred to be due to titanium alone. 

Thermal Neutron Absorption Cross Section. The ease with which a given nuclide can absorb a thermal neutron (energy 33 eV) and become of a different nuclide is indicated by the cross section, given here in units of barns (1 barn = 10-24cm2). If the mode of reaction is other than in, y), it is so indicated, for example, (n,p) or (n, a), where n = neutron, p = proton, y = gamma ray, and a = alpha particle (4He). 

Annihilation can also occur with the emission of three (or more) gamma-rays, and Ore and Powell (1949) calculated that the ratio of the cross sections for the three- and two-gamma-ray cases is approximately 1/370. Higher order processes are expected to be further depressed by a similar factor. A case in point is the four-gamma-ray mode, for which the branching ratio with the two-gamma-ray mode was shown by Adachi et al. (1994) to be approximately 1.5 x 10-6, in accord with QED calculations. 

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