AUTOMATED-SYSTEM FOR NEUTRON-ACTIVATION ANALYSIS DETERMINATION OF SHORT-LIVED ISOTOPES AT THE DOW-CHEMICAL-COMPANYS TRIGA-RESEARCH-REACTOR

An automated neutron activation analysis (NAA) system for the determin ation of short lived isotopes was constructed at The DOW Chemical Comp any's TRIGA Research Reactor in 1993. The NAA group of the Analytical Sciences Laboratory uses the reactor for thousands of analyses each ye ar and therefore automation is important to achieve and maintain high throughput and precision (productivity). This project is complementary to automation of the long-lived counting facilities (see Romick et al ., these Proceedings). Canberra/Nuclear Data Systems DEC-based softwar e and electronics modules and an I/O mounting board are the basic comm ercial components. A Fortran program on a VAX computer controls I/O vi a ethernet to an Acquisition Interface Module (AIM). The AIM controls the gamma spectrometer modules and is interfaced to a Remote Parallel Interface (RPI) module which controls the pneumatic transfer apparatus with TTL signals to the I/O mounting board. Near-infrared sensors are used to monitor key points in the transfer system. Spectra are acquir ed by a single HPGe detector mounted on a sliding rail to allow flexib le and more reproducible counting geometries than with manual sample h andling. The maximum sample size is 8 mi in a heat-sealed two dram via l. The sample vial is nested into a ''rabbit'' vial for irradiation wh ich can be automatically removed prior to spectrum collection. The sys tem was designed to be used by the reactor operator at the control con sole without the aid of an additional experimenter. Applications inclu de the determination of selenium and silver in coal and water, fluorin e in tetra-fluoro ethylene (TFE) coated membranes, aluminum and titani um in composite materials and trace fluorine in non-chlorinated cleani ng solvents. Variable dead time software allows analysis for Se-77m de spite high dead times from N-16 encountered in samples.