Nucleus cross-section

The THM has been recently applied to several reactions whose cross section is crucial for the study of light element abundance in stellar environments. In particular the reactions 6Li(p, a)3He, 7Li(p, a)4He, 9Be(p, a)6Li and 11B(p, a)sBe were studied and the corresponding bare nucleus cross sections were measured. An exhaustive discussion of the experimental results is reported in references [4-7] respectively. 

Neutron wavelength Macroscopic number density Microscopic particle density operator Nucleus cross-section Nucleus coherent cross-section Nucleus incoherent cross-section... 

The absorption and compound elastic cross sections are grouped together as the compound nucleus cross section so. The authors give argu-... 

Target nucleus Cross-section (10 " cm ) Energy release (MeV) Particles released Particle energy (MeV) Range in 1 atm air (cm)... 

Table II. 1. Bound-nucleus cross sections (iO crn ) for neutron scattering...

The analysis of steady-state and transient reactor behavior requires the calculation of reaction rates of neutrons with various materials. If the number density of neutrons at a point is n and their characteristic speed is v, a flux effective area of a nucleus as a cross section O, and a target atom number density N, a macroscopic cross section E = Na can be defined, and the reaction rate per unit volume is R = 0S. This relation may be appHed to the processes of neutron scattering, absorption, and fission in balance equations lea ding to predictions of or to the determination of flux distribution. The consumption of nuclear fuels is governed by time-dependent differential equations analogous to those of Bateman for radioactive decay chains. The rate of change in number of atoms N owing to absorption is as follows ... 

If the force between the beam particle and the target nucleus is assumed to be the Coulomb force, the basic equation for the differential scattering cross-section is given by Rutherford s formula ... 

Table 6.1 shows some other best-fit parameters to Solar-System s-process abundances. The seed nucleus is basically 56Fe light nuclei have low cross-sections (but can act as neutron poisons , e.g. 14N for the 13C(a, n) neutron source), whereas heavier nuclei are not abundant enough to have a major influence. Certain nuclidic ratios, e.g. 37Cl/36Ar and 41K/40Ca, indicate that under 1 per cent of Solar-System material has been s-processed. 

The intensity of a peak in RBS is determined by the cross section o for scattering. At MeV energies, the helium ion penetrates deeply into the atom and approaches the nucleus of the target atom to within 10 4 nm, i.e. well within the radius of the K-electron shell. This means that the scattering event depends only on the Coulomb repulsion between the two nuclei, whereas screening by the electrons (which is important in LETS) plays no role. Thus the scattering cross section is a... 

A consequence of the screening of the nucleus by the electrons is that the cross section for low energy ion scattering varies less steeply with the atomic number than in RBS, where the intensity depends on the atomic number squared. Another difference with RBS is that the scattering intensity is not only determined by the cross section, but also by the probability that an ion is neutralized. 

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