1ST DETECTION OF FALLOUT CS-135 AND POTENTIAL APPLICATIONS OF CS-137 CS-135 RATIOS/

All three cesium isotopes, natural Cs-133 (stable) plus fission Cs-135 (half-life 2.3 Ma) and Cs-137 (half-life 30 y), were measured in two coastal sediment samples using our thermal ionization mass spectromete r equipped with a retarding potential quadrupole lens filter. The Cs-1 35/Cs-133 ratio was about 1 X 10(-9) while Cs-137/Cs-135 was about 0.5 owing to the decay during the past 30 years from their production rat io of about 1. This appears to be the first detection of fallout Cs-13 5 in nature. Being an isotope ratio, Cs-137/Cs-135 is a far more power ful chronometer-tracer than Cs-137 alone. In order to explore its pote ntial, we present briefly two simple models to illustrate how this rat io may be used to quantitatively estimate recent sedimentation and ero sion rates.