Since 1992, Idaho National Engineering and Environmental Laboratory's portable isotopic neutron spectrometry (PINS) system has been widely used for the nondestructive assessment of munitions suspected to contain chemical warfare agents, such as the nerve agent sarin. PINS is a {sup 252}Cf-based prompt gamma-ray neutron activation analysis (PGNAA) system. The standard PINS system employs a partially moderated 5-{micro}g {sup 252}Cf source emitting 10{sup 7} n/s to excite the atomic nuclei inside the item under test. The chemical elements inside the item are revealed by their characteristic gamma-ray spectrum, measured by a high-resolution high-purity germanium gamma-ray spectrometer. The system computer then infers the fill compound or mixture from the elemental data extracted from the gamma-ray spectrum. Reliable PINS assessments can be completed in as little as 100 s for favorable cases such as white phosphorus smoke munitions, but normally, a 1000 to 3000 live-second counting interval is required. To improve PINS throughput when hundreds or more munitions must be assessed, they are evaluating the possible advantages of 14-MeV neutron excitation over their current radioisotopic source.

We have developed a new technique for the detection of neutrons in the presence of a high gamma-ray background. This was accomplished by using two lithium-loaded glass scintillators (/sup 6/Li//sup 7/Li) in combination. The neutron capture reaction in /sup 6/Li has a very high Q-value which means better discrimination against gamma-ray background. The /sup 7/Li detector, on the other hand, is neutron insensitive and was used to measure separately the gamma contribution in a mixed neutron-gamma field. By subtracting this gamma contribution from the /sup 6/Li data, which is sensitive to both gamma rays and neutrons, one can obtain the pure neutron counts.

The newest member of a series of computer programs developed at the INEL for analysis of gamma-ray spectra from Ge semiconductor detectors is GAUSS IX. This program makes use of the computational routines of GAUSS VII in an interactive structure. The interactive features are implemented with OSF/Motif and the X Window System. This interactive version can dramatically decrease the turnaround time for spectral analyses, especially when the user needs to refit some of the peaks with specially-chosen fitting parameters. The graphic features increase the opportunity for detecting patterns and anomalies in the spectral analyses. The user of this program can set up the analysis parameters (i.e., peaks, peak regions, etc.) interactively via window dialogs. The user can interactively display and review the results, selectively re-fit peaks, and save or purge the results, as appropriate. The spectral displays can include the spectral data, peak locations, peak fitting regions, fit curves, and background curves; and the display is completely zoomable, scrollable, and resizable

For treaty verification purposes, due to the hazards of direct sampling of chemical and explosive munitions, non-destructive evaluation methods have important safety advantages. The authors assay method employs neutrons from a californium-252 radioisotopic source to induce capture and inelastic reactions in a munition under test, and the resulting gamma radiation is measured with an high-purity germanium gamma-ray detector. For field verification, a portable, battery-operated assay system has been developed that performs automatic spectrum analysis and agent identification in near-real time. In tests with actual chemical and high explosives munitions, the assay method reliably identifies nerve agents GB and VX, blister agents HD and L, white phosphorous, and high explosives.

Prompt gamma neutron activation analysis (PGNAA) has long been employed for chemical analysis in process streams and laboratories. Recent improvements in the design of germanium gamma-ray spectrometers, the miniaturization of their associated components, and the development of [open quotes]powerful[close quotes] notebook personal computers (PCs) permit the design of PGNAA systems for truly portable in-field use. Portable isotopic neutron spectrometry (PINS) (of gamma rays) was developed at the Idaho National Engineering Laboratory for in-field inspection and verification of chemical weapon inventories where a system that can be carried into an area inaccessible by wheeled transport (rough terrain, confined spaces, etc.) and that is capable of operating on battery power is required. PINS is now also finding use outside of military applications.

A nondestructive assay method to identify chemical warfare (CW) agents and high explosive (HE) munitions was tested with actual chemical agents and explosives at the Toole Army Depot, Toole, Utah, from 22 April 1991 through 3 May 1991. The assay method exploits the gamma radiation produced by neutron interactions inside a container or munition to identify the elemental composition of its contents. The characteristic gamma-ray signatures of the elements chlorine, phosphorus, and sulfur were observed from the CW agent containers and munitions in sufficient detail to make it possible to reliably discern agents GB (sarin), HD (mustard gas), and VX from one another, and from HE-filled munitions. By detecting the presence of nitrogen, the key indicator of explosive compounds, and the absence of elements Cl, P, and S, HE shells were also clearly identified.< >

Sets of high-statistical-quality delayed-neutron energy spectra were obtained from the precursor nuclides /sup 93 -97/Rb covering an energy range from approx. 10 keV to approx. 1300 keV. The data for each of the Rb isotopes show good qualitative agreement with the /sup 3/He ionization chamber data at energies greater than or equal to 200 keV. In addition, they provide definitive spectral information down to approx. 10 keV. Fine structure in this lower energy region with energy resolution much better than that obtained using /sup 3/He ionization chambers was observed, i.e., the FWHM varies from approx. 2 keV at 10 keV to approx. 12 keV at 200 keV. A notable feature the data is that they confirm the existence of strong 14.1 and 26.4 keV lines in the /sup 95/Rb spectrum. Furthermore, the value of 10.4% we obtain for the relative intensity of the 14.1-keV line is significantly greater than the values of 5.9%/sup 3/ and 4%/sup 4/ inferred from /sup 3/He spectrometry.