Comparison of resonance ionization mass spectrometry systems for the determination of ~(135)Cs / ~(137)Cs isotope ratios

摘要

The performance of the Resonance Ionization Mass Spectrometry (RIMS) system at the National Institute of Standards and Technology (NIST) has been compared to a similar system at Pacific Northwest National Laboratory (PNNL). Efficiency and selectivity measurements were performed with both systems and compared to conventional thermal ionization mass spectrometry (TIMS). Determination of the ~(135)Cs / ~(137)Cs ratio was performed using single-resonance excitation 6s ~2S_(1/2) (F = 4)→6p ~2P_(3/2) (F = 5) with an external cavity diode laser followed by photoionization with the 488 nm line of an argon ion laser. Optical selectivity of more than 2 orders of magnitude against stable ~(133)Cs was attained for ~(135)Cs and ~(137)Cs for both systems with an overall selectivity of 10~9 for the PNNL system and 10~8 for the NIST system. Overall efficiencies of 2xl0~(-6) and 5xl0~(-7) were measured for the PNNL and NIST systems respectively. Measurements to determine the chronological age of a nuclear burn-up sample have been performed using both RIMS systems as well as TIMS.