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   COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS        
                   School of Computational Sciences	
                           (CSI 898-Sec 001) 
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            Laser Mass Spectrometry as a Sensitive Tool for 
                     Analysis of Rare Atomic Traces

                            Leticia Pibida
    National Institute of Standards and Technology, Gaithersburg, MD

      Resonant Ionization Mass Spectrometry (RIMS) is a versatile 
analytical technique for determination of rare atomic traces, offering 
outstanding specifications in respect to isobaric suppression, isotopic 
selectivity and overall efficiency. A new RIMS system, specially 
tailored for detection of radioisotopes in environmental samples, is 
under development at the National Institute of Standards and Technology
 (NIST), which uses a glow discharge source and continuous-wave (cw) 
lasers for ionization. The system is presently tested with cesium to 
characterize its performance, future applications on other radioisotopes 
of interest, e.g. 239,240Pu, are foreseen. As a demonstration of the 
capabilities of this method, the isotopic ratio of 135Cs/137Cs in nuclear 
waste was investigated by cw-RIMS in collaboration with a group at 
Pacific Northwest National Laboratories (PNNL), demonstrating extreme 
suppression of background and isobaric interferences. While, due to its 
long half-life 135Cs can be used as a valuable tracer for long-term 
observations of geochemical evolution, monitoring of the isotopic ratio 
of 135Cs/137Cs in nuclear waste and environmental samples can reveal their 
possible release pathways. The extraordinary potential of cw-RIMS for 
selective ultratrace analysis of many other long-lived radionuclides, 
i.e. 41Ca, 90Sr, 99Tc, 239Pu, will be outlined.

                        Monday , September 25, 2000
                                  4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served.
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Find the schedule at http://csi.gmu.edu/lcdm/seminar/schedule.html