AUTOMATION OF THE GAMMA-RAY SPECTROSCOPY COUNTING SYSTEM AT THE DOW-CHEMICAL-COMPANY ANALYTICAL-SCIENCES-LABORATORY

The neutron activation analysis group within the Analytical Sciences L aboratory analyzes 3000-5000 samples annually for a wide variety of an alytes. Due to the high sample load, it is imperative that the gamma s pectroscopy counting system be automated to maximize the efficiency of the system while ensuring the accuracy of the analyses. Using a Zymar k robotic system, Compumotor drives, and DEC-based Canberra/Nuclear Da ta software we have automated sample changing, detector positioning, a nd data acquisition. Automation of these functions has resulted in a m ore consistent counting geometry, minimized crosstalk between samples, and accurate repositioning of the detectors for standardless quantita tive analysis. The Zymark robotic system currently controls two detect or systems, but is designed to control up to three independent detecto r systems. Canberra/Nuclear Data software, operating on a Microvax 310 0, issues commands to the Zymark controller to change samples when spe ctral acquisition is complete. Once a new sample is in place, the robo t sends a signal to the Microvax to begin data acquisition. Up to 40 s amples, with sizes between 1 and 20 mi, can be accommodated using cust omized sample racks and sample holders. The location of the sample rac ks relative to the detectors has eliminated noticeable crosstalk betwe en samples in the racks and samples being counted. The two HPGe detect ors for each detector system sit on motorized platforms controlled by programmable Compumotor drives. Programmed function keys move the dete ctors in or out at fixed increments to optimize sample/detector geomet ry. The high resolution of the stepper motors enables accurate reposit ioning of detectors so that previously acquired standard spectra can b e compared with samples activated and counted under identical conditio ns but at different times.