THE OVERALL GOAL OF THIS PROJECT IS TO IMPROVE THE SENSITIVITY AND PRECISION FOR PLUTONIUM ISOTOPE RATIO MEASUREMENTS BY THERMAL IONIZATION MASS SPECTROMETRY (TIMS) USING A NOVEL POLYMER FIBER PLATFORM. DESPITE THE ULTRAHIGH SENSITIVITY PROVIDED BY TIMS FOR ISOTOPIC ANALYSES OF PU, SAMPLE UTILIZATION IS GENERALLY LOW (<1% EFFICIENCY). CARBON-BASED ADDITIVES AND ANION EXCHANGERS CAN IMPROVE THERMAL IONIZATION EFFICIENCIES FOR PU; HOWEVER, THE UNDERLYING MECHANISM(S) ARE NOT WELL UNDERSTOOD. PRELIMINARY DATA HAVE INDICATED THAT POLYMER FIBERS HAVE GREATER PRECISION AND SAMPLE UTILIZATION THAN TRADITIONAL BEAD LOADING OR POROUS ION EMITTER SOURCES. THE SIGNIFICANCE OF THIS PROJECT IS THAT IT WILL IMPROVE THE UNDERSTANDING OF THE ROLE(S) OF CARBON SOURCE PROPERTIES ON IONIZATION EFFICIENCY IN TIMS. ARMED WITH THIS KNOWLEDGE, CARBON SOURCES MAY BE DESIGNED RATIONALLY TO IMPROVE MEASUREMENT SENSITIVITY/PRECISION, WHICH WOULD REDUCE THE REQUIRED SAMPLE SIZE FOR ANALYSIS OF PU FROM ENVIRONMENTAL SAMPLES.