Nuclear Reaction Cross Sections

NRA as in RBS or ERDA, and possible modification of the target composition as a result of irradiation must be considered. Nuclear reaction cross-sections are also usually not available in analytical form for direct evaluation of measured data. Concentrations are, therefore, often obtained by comparison of the measured data with results from standard samples of known concentration. 

Detailed information about specific nuclear reactions at different stages of stellar evolution and the measurement of nuclear reaction cross-sections is given (together with a good overview of the whole of astrophysics) in... 

These reactions, called inverse (3 decay, were obtained by adding the antiparticle of the electron in the normal (3 decay equation to both sides of the reaction. When we did this we also canceled (or annihilated) the antiparticle/particle pair. Notice that other neutrino-induced reactions such as ve + n —> p+ + e do not conserve lepton number because an antilepton, ve, is converted into a lepton, e. Proving that this reaction does not take place, for example, would show that there is a difference between neutrinos and antineutrinos. One difficulty with studying these reactions is that the cross sections are extremely small, of order 10-19 bams, compared to typical nuclear reaction cross sections, of order 1 barn (10—24 cm2). 

Figure 7 is a graphic description of the kinetic energy required by a deuteron to produce D-D, D-T, and D-helium-3 nuclear reactions. The bottom of the chart depicts the required deuteron kinetic energy level in thousands of electron volts. The x-axis coordinate is labeled from 10° to 103 kilo-electronvolts. The y axis is labeled in terms of the nuclear reaction cross section. Three types of nuclear reaction curves are depicted. Note that each curve rises to a maximum and then decreases in value. The D-D curve is shown with its maximum value at about 1000 keV. Considering the use of a typical ion accelerator, electric potentials ranging from about 10 to 106 keV are used. 

The Importance of Level Structure In Nuclear Reaction Cross-Section Calculations... 

Activation analysis is based on the production of radioactive nuclides by means of induced nuclear reactions on naturally occurring isotopes of the element to be determined in the sample. Although irradiations with charged particles and photons have been used in special cases, irradiation with reactor thermal neutrons or 14 MeV neutrons produced by Cockcroft-Walton type accelerators are most commonly used because of their availability and their high probability of nuclear reaction (cross section). The fundamental equation of activation analysis is given below ... 

In order to determine the half-life, the decay scheme, and other nuclear characteristics of a radioactive nuclide, it is important to use a sample of very high radiochemical purity. In addition in the measurement of nuclear reaction cross sections, fission yields and in activation analysis, the amounts of the radioactive nuclide produced must be determined. Thus It Is also necessary to determine the yield of... 

The second group includes radioisotopes produced by cosmic rays. The rates of production of radioactive isotopes can be estimated reasonably well from the energy spectra of primary and secondary cosmic rays and a knowledge of the corresponding nuclear reaction cross sections. 

Nuclear Reaction Isotope Abundance L Ei or He] Nuclear Reaction Cross Section Recoil Energy, Tritium Atom Recoil Energy, Emitted Particle Tritium atoms produced/sec Irradiation at 10 n/cm /sec Disintegration rate of H produced in one second... 

The F-factor can be calculated according to eqn [15] if (1) the stopping power of sample (Sx) and standard (Ss) and (2) the nuclear reaction cross-section (cr) are known, both as a function of energy in the energy interval between the threshold energy (Ej)... 

As the second condition is not always fulfilled, two approximative standardization methods have been proposed that do not require knowledge of the nuclear reaction cross-section. The first approximative method makes use of stopping power data for sample and standard. 

No general statement can be made about the elements that can be determined and the samples that can be analyzed, because these depend on the nuclear characteristics of the target nuclide (isotopic abundance), the nuclear reaction (cross-section and related parameters such as threshold energy and Coulomb barrier), and the radionuclide induced (half-life, radiation emitted, energy, and its intensity) for the analyte element, the possible interfering elements and the major components of the sample. CPAA can solve a number of important analytical problems in material science (e.g., determination of boron, carbon, nitrogen, and oxygen impurities in very pure materials such as copper or silicon) and environmental science (e.g., determination of the toxic elements cadmium, thallium, and lead in solid environmental samples). As these problems cannot be solved by NAA, CPAA and NAA are complementary to each other. 

Significance of Nuclear Reaction Cross Section Data.1906... 

The nuclear reaction cross section data are needed in radioisotope production programs mainly for optimisation of production routes, i.e., to maximize the yield of the desired product and to minimize the yields of the radioactive impurities. From a given excitation function, the expected yield of a product for a certain energy range, i.e., target thickness, can be calculated using the expression ... 

Fora detailed discussion of various experimental and theoretical aspects of nuclear reaction cross section data relevant to cyclotron production of radionuclides, the reader is referred to two recent IAEA-coordinated efforts (cf. Gul et al. 2001 Qaim et al. 2008). 

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