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The possibility of transformation of energy of fast and epithermal neutrons to energy of coherent photon radiation at the expense of a neutron pumping of the active medium formed by nucleus with long-living isomerous states is theoretically described. The channel of the nucleus formation in isomeric state as a daughter nucleus resulting from the nuclear reaction of neutron capture by a lighter nucleus is taken into consideration for the first time. The analysis of cross sections dependence of radiative neutron capture by the nuclei of gadolinium isotopes Gd155 and Gd156 is performed. As a result, it is stated that the speed of Gd156 nuclei formation exceeds the speed of their “burnup” in the neutron flux. It is provided by a unique combination of absorbing properties of two isotopes of gadolinium Gd155 and Gd156 in both thermal and resonance regions of neutron energy. The possibility of excess energy accumulation in the participating medium created by the nuclei of the pair of gadolinium isotopes Gd155 and Gd156 due to formation and storage of nuclei in isomeric state at radiative neutron capture by the nuclei of the stable isotope with a smaller mass is shown. It is concluded that when the active medium created by gadolinium nuclei is pumped by neutrons with the flux density of the order of 1013 cm-2·s-1, the condition of levels population inversion can be achieved in a few tens of seconds. The wave length of the radiation generated by the medium is 0.0006 nm.

The possibility of the Gadolinium nuclei energy levels population inversion under neutron bombardment is theoretically shown. In the process two isotopes of gadolinium take part. Light isotope Gd155 capturing neutron transforms to heavy isotope Gd156 at that heavy nucleus is in an excited metastable state. The population inversion is investigating during several tens of second when the neutron flux intensity is 1013 cm-2 · s-1.

Gadolinium (Gd) has two isotopes which are strong neutron absorbers. It would be desirable to enrich Gd in those isotopes for use in nuclear fuels. Isotope‐selectivity based on spectral isotope shifts has been investigated. Our experimental results indicate that significant enrichment is achievable even with relatively broadband (≊3 GHz) lasers. © 1995 American Institute of Physics

A method based on polarization selectivity and three step laser photoionization is presented for separation of the odd isotopes of gadolinium. Measurements of the spectroscopic parameters needed to quantify the excitation pathway are discussed. Model results are presented for the efficiency of photoionization. The vapor properties of electron beam vaporized gadolinium are presented which show dramatic cooling during the expansion of the hot dense vapor into a vacuum. This results in a significant increase in the efficiency of conversion of natural feed into enriched product in the AVLIS process. Production of enriched gadolinium for use in commercial power reactors appears to be economically viable using technology in use at LLNL.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A multistep photoionization with three resonant polarized photons has been used to separate the odd and even isotopes of gadolinium. Due to their hyperfine structure (I= 3 2 ), the 155,157Gd isotopes can be photoionized via a J=2→2→1→0 scheme with three п photons whereas the even isotopes cannot. If a time delay is introduced between the three laser pulses we show that the presence of a low intensity dc magnetic field affects the selectivity. The effect of this weak field on the 156Gd photoionization rate has been calculated independently of the optical pumping and the result is in good agreement with the experiment.

The cross sections for Coulomb excitation and the energies of the accessible low-lying rotational states in the six most abundant isotopes of gadolinium have been determned from measurements on the corresponding groups of inelastically scattered protons and deuterons. The projectiles were accelerated in an electrostatic generator to energies around 4 Mev. Particles scattered from isotopically pure targets prepared in an isotope separator were observed at an angle of 145 deg with respect to the beam by means of a magnetic spectrometer of high resolution. The lifetimes for the first excited states in Gd/sup 154/ and Gd/sup 156/ derived from the measured cross sections are in good agreement with the reported directly measured lifetimes of these states. (auth)

Selective excitation of odd isotopes of gadolinium has been carried out using two-colour photoionisation schemes. A new parameter ηsel-ion is defined for identifying optimum frequency positions for both excitation steps, where good isotopic selectivity can be achieved without significant sacrifice in the ion yield. The abundance of 155 Gd and 157 Gd isotopes were theoretically calculated and experimentally verified. All five photoionisation schemes are found to be useful for the selective ionisation of 155 Gd and 157 Gd isotopes.