Technical Report on Selective Laser Ionization
Résumé
The SMILES project (Mass Separation Coupled with Laser Ionization for Environmental and Health Applications) aims to quantify, purify or separate isotopes for health and environmental applications using the laser ionization technique coupled with mass separation.
This report focuses specifically on laser beam resonant ionization which was first demonstrated and experimented at the LNPI (Leningrad Nuclear Physics Institute) in 1988 and which selectively and efficiently promotes atoms into their excited and ionized states by photoionization.
We are particularly interested in the performance that instruments, using this technique, can achieve:
-A high selectivity: isobaric deletions are greater than 108, only due to multi-step optical transitions, and greater than > 1013 by combining laser ionization with mass separation. Indeed, laser ionization is selective according to the atomic number Z while the application of an electromagnetic field ensures the separation of the isotopes according to their mass A, the combination of the two thus making it possible to isolate a given isotope (Z, A) with great precision.
-An ionization efficiency between 10-3 and 10-1 that is due to the high optical cross-section values that generate high ionization and excitation probabilities.
-A high sensitivity that can reach detection limits of fg, and even ag.
For the SMILES project, the experimental set-up, as a whole, will have to adapt to the diversity of samples encountered within a large community of users in various disciplinary fields (environment, medicine, physics, chemistry…). The experiments planned will first concern the analysis of stable isotopes or very low activities radioisotopes at the ultra-trace scale. A first list of elements of interest has already been established: Stable Cu-(63/65), Er, Pb, Am, Pu, Ra-226/Ra-228 (but also interest in a Ra-228 source), Pb-210, Th-230, U-236,...
The primary aim of this report is to define the technical requirements for the selective laser ionization device of the SMILES project by presenting initial specifications of the selective laser ionization system as it will be implemented.
After presenting two possible configurations of the experimental set-up, the various elements of this system will be reviewed: pump laser, Ti:Sapphire cavities, frequency conversion units, optical paths, system control such as laser diagnostics, spatial and temporal overlapping of laser pulses,… as well as the main technical characteristics of the future "Laser room”.
Finally, a series of “open questions” is addressed to the expert committee in order to validate and improve the technical solutions to be implemented for the SMILES selective laser ionization system.
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