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A quantum-mechanical formalism to calculate the nuclear excitation by electron transition (NEET) is presented. Emphasis is on the explicit calculations of the transition matrix elements for electric multiple and magnetic dipole NEET and discussions of the selection rules. One of the features of this formalism is that the part of the matrix element in connection with the nuclear partner is related to the nuclear partial radiative width, which is a measurable quantity. This makes it available to evaluate the NEET probability more reliably. The predicted results for NEET probabilities in {sup 189}Os, {sup 197}Au, and {sup 237}Np are given along with the available measured data.

The physical processes about x-ray emission, Auger electron emission, and nuclear excitation by electron transition (NEET) induced by deexcitations of the excited atomic states, e.g., the inner shell hole states, are studied self-consistently in the unified nonrelativistic quantum mechanics framework. The emphasis is on exploring the NEET process and its interference with the other two processes. The transition probabilities of these deexcitation channels are given in analytical forms. The numerical calculations for $_{76}^{189}\mathrm{Os}$, $_{79}^{197}\mathrm{Au}$, and $_{93}^{237}\mathrm{Np}$ have been done and compared with the available experimental results.

The time-dependent fields experienced by a nucleus as it passes through a crystal can cause transitions to excited nuclear states. The transition rate is especially large when the speed of the nucleus satisfies a resonance condition. Previous estimates of the nuclear excitation rates have been based on symmetry arguments and experimental data for related processes. We present here a calculation of the nuclear excitation rate which does not rely on these simplifying approximations. Using nonrelativistic quantum mechanics, the excitation cross sections of highly stripped nuclei channeled along the Si[l angle]110[r angle] crystal axis have been calculated. The results are smaller than those given by previous estimates by several orders of magnitude. We note that there are similarly large discrepancies between different theoretical and experimental results for other phenomena involving coupled electronic and nuclear transitions. The reason for these disagreements is not clear.

A formalism calculating the cross sections of intermediate-energy proton direct capture populating continuum states has been developed. The transition amplitude includes two terms corresponding to potential-scattering to potential-scattering transitions and potential-scattering to resonance-scattering transitions, respectively. The model is compared with available experimental data of the $^{11}\mathrm{B}$(p,${\ensuremath{\gamma}}_{19}$${)}^{12}$C reaction, and the results show that within the reasonable parameter limit the direct capture mechanism is able to account for a major feature of the measured data, and, in the present case, the contributions from the two terms are of the same order of magnitudes. The physical significance of the results is discussed.

Based upon a consistent description of the wave functions of the captured state and the final state, a unified formalism has been established to investigate the nonstatistical effects in radiative nucleon capture reactions at energies ranging from 0.1 to 20 MeV. This model includes the direct-semidirect capture and radiative capture in the compound elastic and inelastic channels. By applying this model theory and including also the statistical contributions of the compound-nucleus process, the radiative neutron capture cross sections in {sup 27}Al, {sup 55}Mn, {sup 89}Y, and {sup 208}Pb have been calculated and the results are compared with the measured data. We have also investigated the relative importance of the operation for each nonstatistical mechanism in the total capture cross sections.

This paper investigates the mass, shell, and even-odd effects in the nonstatistical and statistical contributions to the radiative nucleon capture reactions. The ({ital n},{gamma}) cross sections for 32 even-neutron target nuclei were studied at {ital E}{sub {ital n}} of 0.1 to 3 MeV. The results indicate that the nonstatistical capture cross sections do not present any remarkably varying pattern with mass number. The statistical capture cross sections, which depend strongly on the level density, display marked mass, shell, and even-odd effects. The nonstatistical fractions show prominent downward tendency with mass number, as well as the shell effect.

This paper investigates the nonstatistical effects in radiative neutron capture cross sections for nuclides at the 2p size resonance region of neutron strength function, specifically /sup 27/Al(n,..gamma..) and /sup 28/Si(n,..gamma..) reactions. The neutron energies studied range from thermal up to 2 MeV. The calculated results show that in comparison with medium and heavy nuclei, the nonstatistical fractions in the total capture cross sections for the two lighter nuclides are extremely large. In the thermal energy region, the fractions are about 50%. In the resonance energy region, the averaged contributions from the nonstatistical processes are considerably larger than that from the statistical mechanism. The physical significance of the results was briefly discussed. It was also indicated that this conclusion is qualitatively consistent with the fact that the measured capture data show significant correlations in both nuclides.