Focus And by using a narrow-band laser, the velocity distribution of the particles can be measured. This makes it possible to determine the mechanism of re-
lease, because a particle released in a thermal process has a much lower energy distribution than a particle released in a sputtering process.
RIMS: Nuclear Analysis
A scientist at Argonne National Laboratory tunes a laser used to study fusion plasmas. If too many impurities get into the plasma, they can stop the fusion reaction introduction and the properties of the plasma edge, the boundary region between the plasma and the wall of the tokamak. In the studies performed to date, the researchers have looked at impurities such as Fe, Ti, and Al. "In the future," says Roberto, "we plan to turn our attention to hydrogen and to the lighter impurities, such as carbon and oxygen. Hydrogen will be studied both in the excited state, with existing lasers, and in the ground state, requiring a Lyman alpha laser, which has only recently become available." In other recent work, Clifford H. Muller at General Atomic has shown that it is possible to measure ion temperatures in a tokamak by looking at the Doppler-broadened absorption spectra of excited H in the plasma. This technique thus provides a "thermometer" that can be used to determine the temperatures attained in a particular experiment. And Zr has been detected in a plasma experiment at Argonne National Laboratory. According to C. E. Young at Argonne, the Zr experiment was "the first in what we plan to be a long sequence." The laser-induced fluorescence technique, explains Roberto, "allows you to detect neutrals as well as ions. This is very important, because most of the particles released from the tokamak wall are released first in the neutral state and are then ionized as they proceed into the plasma. LFS thus allows you to study the release of impurities at the source." Other advantages, according to Roberto, include the fact that the technique does not disturb the plasma, so one can do plasma-independent measurements.
Resonance ionization mass spectrometry (RIMS) is a technique that has recently emerged from the analytical marriage of resonance ionization spectroscopy (RIS) and mass spectrometry. In the past few months, researchers have applied RIMS to the determination of a number of lanthanides and actinides in the presence of interferences. In RIS, the technique that made single atom detection a reality, atoms in the gas phase are ionized by photons tuned to highly specific electronic quantum transitions of those atoms. One ion and one electron are produced in each ionization event, and RIS is concentrated on the detection of the liberated electrons (1,2). In RIMS, on the other hand, further analytical information is generated by directing the resulting ions into the analyzer of a mass spectrometer. The combination of the two techniques provides two modes of elemental selectivity, involving both the specificity of the tuned laser and the resolving power of the mass analyzer. D. L. Donohue and J. P. Young of Oak Ridge National Laboratory (ORNL) have been working on a number of applications for the technique, including the determination of isotopes of Nd in the presence of isobaric Sm (Sm isotopes of the same nominal atomic mass). Rare earth elements are traditionally difficult to separate from each other by chemical means, and there is nearly always some Sm present as an interfèrent in determinations of Nd. The elimination of this interference with RIMS thus represents a significant development, especially to those interested in nuclear reactor design and performance evaluation, since Nd concentration is a particularly good indicator of the number of fissions that have occurred in the course of nuclear fuel irradiation (3). Recently, Donohue and Young have also demonstrated the applicability of RIMS to the determination of Pu, with the potential for elimination of isobaric U and Am interferences that commonly plague this procedure (4). Other work is proceeding at Los Alamos National Laboratory, where C. M.
1476 A · ANALYTICAL CHEMISTRY, VOL. 54, NO. 14, DECEMBER 1982
Optical path of RIMS instrument at ORNL is shown. A N2 pump laser is on the left, a dye laser is in center foreground, the MS ion source is in center background, and the magnetic sector of the MS is on the right Miller et al. have demonstrated the selective ionization of Lu in the presence of Yb (5). And a group at the National Bureau of Standards has set up a system and is currently investigating RIMS for its potential applicability to more sensitive and selective isotope ratio measurements (6). The group at ORNL writes (3) that "future work in RIMS will seek to extend its application to other elements of interest in nuclear, environmental, or geological samples. The high selectivity of RIMS means that trace amounts of certain elements can be measured in complex matrices without the need for timeconsuming chemical separation." References (1) Young, J. P. et al. Anal. Chem. 1979, 51,1050-60 A. (2) Hurst, G. S. Anal. Chem. 1981,53, 1448-56 A. (3) Donohue, D. L.; Young, J. P.; Smith, D. H. Int. J. Mass Spectrom. Ion Phys. 1982,43,293-307. (4) Donohue, D. L.; Young, J. P. Anal. Chem., accepted for publication. (5) Miller, C. M.; Nogar, N. S.; Gancarz, A. J.; Shields, W. R. Anal. Chem. 1982, 54, 2377-78. (6) Fassett, J. D.; Travis, J. C; Moore, L. J.; Lytle, F. E., submitted for publication in Anal. Chem.
