Isotope multistep ionization

In those years investigators attention was centered primarily, with a few exceptions, on the use of selective ionization precisely for isotope separation purposes. Today we know that the resonance multistep ionization technique is the most sensitive method for studying the isotopic and hyperfine structures of atoms with short-lived nuclei available in very small quantities, for laser on-line separation of nuclear isomers, and for detection of traces of some elements. 

Fig. 9.10 Laser multistep ionization detection of the rare isotope He. (a) Scheme of two-step isotopically selective excitation of He (b) ion signal as a function of the second-step laser frequency with the first-step laser frequency in resonance with the He isotope (c) first-step...

Isotope-selective multistep ionization of the vapor by means of several tunable lasers. To provide predominant ionization of the desired isotope, these lasers should have a very narrow linewidth and should be tuned very accurately in resonance with the necessary transition frequencies of this isotope. Also, the laser frequencies should be sufficiently stable. 

Fig. 9.11 Schematic illiastration of resonant multistep ionization of radioactive atoms in a hot cavity (laser ion source) and following mass separation with selectivity by element (Z), isotope N), and isomer AE).

The measurement of isotope shifts and hyperfine structure (hfs) is possible in multistep laser excitation and ionization if one of the excitation lasers in the excitation schemes shown in Fig. 2 is a narrow band laser and if a collimated atomic beam is used as the source of absorbing atoms. The rest of the aparatus can remain as used for other studies. The narrow band laser(s) may be a pressure tuned pulsed dye laser ( 100 MHz, 0.003 cm l) or a CW dye laser (30 MHz to 30 KHz, 10- to 10 6 cm-- -). The atomic beam should be collimated to reduce "Doppler" broading to the level required to attain the resolution needed for investigating the structure and to fully utilize the narrow band width of the laser. A band width of 10cm-- - is usually adequate for most investigations of lanthanides and actinides. A portion of the scan laser beam is directed to an etalon and detector (interferometer) to provide relative frequency calibration. 

Published isotope shift data for actinides obtained by multistep laser excitation and ionization is confined to the 5915 A transition of uranium. (2) Much improved resolution and precision were obtained by Childs, Poulsen and Goodman(22) using their laser-atomic beam fluorescence method. 

Laser isotope separation is one area where multistep excitation and ionization has great commercial potential. The research and development efforts in atomic vapor laser enrichment of 235y are a major factor contributing to the current research activities in laser excitation and ionization processes. The first paper on selective multistep photoionization of atoms was published in 1971. (.62) Since then numerous review articles( 15, 16 >L7,63 >54, (i5) ave been written on laser isotope separation and, in each review, there is a section on atomic vapor photoionization processes. The subjects of economics and critical parameters have been well covered in previous reviews and will not be discussed in detail here. We... 

Because the CO2 containing carbon-14 is used to trace the progress of carbon through the reaction, it is referred to as a radiotracer. A radiotracer is a radioisotope that emits non-ionizing radiation and is used to signal the presence of an element or specific substance. The fact that all of an elements isotopes have the same chemical properties makes the use of radioisotopes possible. Thus, replacing a stable atom of an element in a reaction with one of its isotopes does not alter the reaction. Radiotracers are important in a number of areas of chemical research, particularly in analyzing the reaction mechanisms of complex, multistep reactions. 

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