USE OF A FRISCH GRID IONIZATION CHAMBER TO RAPIDLY CHARACTERIZE AND QUANTIFY a-EMITTING ACTINIDES IN UNPROCESSED SOILS, LIQUIDS, SOLIDS AND AIR-DUST SAMPLES*.

Salvatore C. Scarpitta, Analytical Services Laboratory, BNL

Robert P. Miltenberger, Rad-Con Division Facilty Support, BNL

Nina Carte, University of Connecticut

A 5 inch diameter Frisch Grid (FG) pressurized ionization chamber is being utilized at Brookhaven National Laboratory (BNL) to characterize and quantify a-emitting actinides present in unprocessed liquids, soils, solids (metal, brick, concrete) and air-dust matrices. Samples were obtained from the BNL Graphite Research Reactor Decommissioning Project and were radiologically contaminated with nCi to uCi per killogram amounts of ^239/40Pu, ²⁴¹Am and/or ^235/238U (as well as other b /g emitters). Spectra and analytical data will be presented for various matrices showing the quality of results that can be obtained using gram amounts of unprocessed sample counted for less than 1 hour. The Data Quality Objectives for the characterization phase of this project were such that no separation chemistry (with added yield tracer) was required. Consequently, semi-quantitative results were deemed acceptable with the added advantage that the amounts of waste generated from this rapid analysis were virtually nil.

Initially, various matrices of non-contaminated BNL samples, including urine, were spiked with a-emitters ²³⁰Th (4.6 MeV), ²³⁶Pu (5.8 MeV) and ²⁴³Am (5.3 MeV) in order to determine a-peak resolution and to establish matrix-specific energy calibration curves. Alpha detection efficiencies were constant over a 3 to 9 MeV a-energy range and were typically 0.15 cpm dpm^-1 for 20-40 mg amounts of soil, 0.18 cpm dpm^-1 for cellulose-nitrate membrane air-filters and 0.45 cpm dpm^-1 for 1 mL amounts of evaporated (spiked) de-ionized water samples. Optimum a-peak resolution and detection efficiencies were obtained when the absorber thickness was maintained below 400 ug cm^-2 on either 5 cm diameter stainless steel and aluminum planchets or 4.5 cm diameter membrane filters. FWHM was typically 0.050 to 0.075 MeV for mass-less samples. Instrument background over a 1200 channel a-energy range of 3-9 MeV is very low at 36 cph. The MDLs for a 1 hr count (at optimum a-efficiency and using a 0.150 MeV region-of–interest) were: 15 pCi g^-1 for 40 mg soil, 0.2 pCi mL^-1 for 1 mL water, 0.4 pCi filter^-1 and 1 pCi mL^-1 for a 0.2 mL evaporated urine sample.

A homogeneous (<200 mesh) spiked soil containing < 10,000 dpm g^-1 each of ^239/40Pu, ²⁴¹Am and natural U will be obtained from RESL, a U.S. DOE reference laboratory. The sample will be submitted to both FG analysis (at BNL) and to an off-site laboratory that will use EML’s HASL-300 actinide separation procedure in conjunction with a-spectroscopy. Using this rad-fortified soil as a “worst-case matrix” scenario, comparative results will be presented as one measure of accuracy for this rapid nuclide-specific-actinide a-counting technique. Quantitative results will also be compared for a BNL smear and filter sample containing ²⁴¹Am, measured by Gross a/b, g and FG analysis.

*Work supported by Brookhaven Science Associates (BSA) and the U.S. DOE’s Energy Research University Laboratory Fellowship (ERULF) Summer Intern Program. Purified actinide tracers provided by Dr. Isabel M. Fisenne, U.S. DOE Environmental Measurements Laboratory (EML).