FAST, LOW-LEVEL DETECTION OF SR-90 AND SR-89 IN ENVIRONMENTAL-SAMPLESBY COLLINEAR RESONANCE IONIZATION SPECTROSCOPY

Environmental assessment in the wake of a nuclear accident requires th e rapid determination of the radiotoxic isotopes Sr-89 and Sr-90. Usef ul measurements must be able to detect 10(8) atoms in the presence of about 10(18) atoms of the stable, naturally occurring isotopes. This p aper describes a new approach to this problem using resonance ionizati on spectroscopy in collinear geometry, combined with classical mass se paration. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an iso topic selectivity of about 10(6). The ions are then neutralized by cha rge exchange and the resulting fast strontium atoms are selectively ex cited into high-lying atomic Rydberg states by narrow-band cw laser li ght in collinear geometry. The Rydberg atoms are then field-ionized an d detected. Thus far, a total isotopic selectivity of S > 10(10) and a n overall efficiency of xi = 5 x 10(-6) have been achieved. The desire d detection limit of 10(8) atoms Sr-90 has been demonstrated with synt hetic samples.