NUMERICAL EVALUATION OF THREE-STEP SELECTIVE PHOTO-IONIZATION OF GD157 AND GD155 ISOTOPES

Document Type: Regular Paper

Authors

Department of Physics, Iran University of Science and Technology, Narmak, Tehran, I. R. of Iran

Abstract

A three-step selective photo-ionization for Gd155 and Gd157 isotopes by pulsed laser was
evaluated numerically. Due to large thermal neutron absorption cross sections, these two isotopes in
natural gadolinium are good candidates as burnable poison to control reactivity early in the fuel cycle
and allow extended fuel burn up. Rate equations have been used to calculate the dynamics of the isotope
populations, ionization rate, and selection factor. Doppler broadening, as well as power broadening for
atomic energy levels, has been considered in the calculations. The effects of laser intensity, frequency
bandwidth, and laser detuning in the ionization process have also been assessed. By applying a variety of
conditions, the sensitivity of different parameters in the ionization process was investigated. The results
show that the ionization yield increases with the intensities of lasers, and becomes saturated at some
specific values. Depending on the energy bandwidth of each state, laser bandwidth and the detuning of
lasers greater than particular values can affect the ionization yield. Due to small and finite isotope shifts
of energy states, the selection factor can be influenced by detuning and laser bandwidth. From the
results, it can be inferred that for Gd155 and Gd157 isotopes, ionization is more sensitive to the first and
second laser bandwidth and detuning. From these results, optimum selection factors and ionization by
using appropriate laser intensities, bandwidth, and detuning can be achieved.

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