A g-g COINCIDENCE SPECTROMETER FOR INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

 

Bryan E. Tomlin, Richard M. Lindstrom, and Rolf Zeisler

 

The accurate and precise quantitative determination of trace elements in biological, environmental, and industrial materials is of significant importance.  However, the chemical form of the analyte in complex sample matrices limits many analytical methods.  Techniques like instrumental neutron activation analysis (INAA) and prompt gamma ray activation analysis (PGAA) are based upon nuclear rather than chemical properties of the analyte.  Over several decades these techniques have proven to be sensitive and selective tools for the determination of many elements.

Despite the maturity and advantages of neutron activation analysis, further improvements are possible.  Just as in other types of analysis, the key to improving activation analysis is increasing the signal-to-noise ratio.  The technique of gamma-gamma (g-g) coincidence spectrometry, a means of counting gamma rays with a much higher level of discrimination, provides the ability to significantly improve the signal-to-noise ratio.  The application of g-g coincidences to INAA and PGAA provides several distinct improvements.  First, a reduced gamma-ray spectrum background can be obtained, leading to increased sensitivity and lower detection limits for certain elements.  Secondly, a reduction in direct interferences leads to increased selectivity.

Nuclear spectroscopists commonly employ g-g coincidence techniques, but this technique is not as well known within the nuclear analytical community.  Some preliminary work has been done in regard to the use of g-g coincidence measurements as a means of improving the sensitivity of PGAA; however, less development of the technique in relation to INAA has occurred.  New trends in instrumentation promise greater improvements than have been achieved in the past.

The present research involves the development of g-g coincidence spectrometry to improve detection limits and selectivity of INAA for several elements.  This system will extend to quantitative analyses the general approaches used by nuclear spectroscopists using state-of-the-art signal processing procedures.  A detection system has been constructed, all parameters are being optimized for quantitative analysis of activated samples, and the method will be validated for specific analytical applications.  The advantages that can be attained by this program include:  the ability to assay trace elements without radiochemical separations, thereby reducing analysis time and decreasing radiation exposure; improved detection limits and selectivity for a number of elements; and the ability to perform multi-element analyses with high sensitivity.

 

 

Postdoctoral Associate:  Bryan E. Tomlin

Mentor:  Richard M. Lindstrom

Division:  839.01

Laboratory:  CSTL

Building/Room:  Building 235, Room B172

Mail Stop:  8395

Tel:  (301) 975-6283     Fax:  (301) 208-9279

Email:  bryan.tomlin@nist.gov

Sigma Xi member:  no

Category:  chemistry