Zhichao Lin

Conference Report: NIST Speciation Workshop - Gaithersburg, MD June 13-15, 1995

program has been successful in making available to the community natural matrix materials that are very useful for the evaluation of radiochemical-measurement techniques. Traditionally, measurements of environmental radi ological contamination have focused on the determination of total concentrations, a very useful tool for initial site characterization of impacted areas. It is clear, however, that total concentration does not describe the environmental behavior or bioavailability of contaminating radionuclides. Rather, the time-dependent spread of radi ological contaminants is a function of ‘‘partitioning’’ or ‘‘speciation’’ of radionuclides within soils and sediments. In the United States and many other parts of the world, there remains an enormous task ahead for remediating radi ologically contaminated environments and monitoring the impact of man-made radioactivity on the natural environment. The U.S. Department of Energy (DOE) faces contamination plumes of greater than 2.3 10 m of contaminated groundwater and greater than 150 310 m of contaminated soil (Wyrick, SAIC, workshop presenter). Furthermore, current technologies for cl eaning up and preventing further migration of radioactive contaminants are costly and often ineffective. The development of strategies for remediation, restoration, and mitigation of radi ologically contaminated areas is necessarily constrained by budgetary concerns. Therefore, for long-term risk assessment analyses, regulatory bodies need information which takes the mobility and bioavailability of radi ological contaminants into consideration. Although the need exists for the continued development of more accurate, efficient, and sensitive radioanalytical techniques, there is also a need for more information concerning what fraction of the contamination in a given environmental sample is ‘‘environmentally available.’’ Presently, there is no acceptable measure of the bioavailability of radioactive elements in contaminated soils and sediments [1].

Certified reference, intercomparison, performance evaluation and emergency preparedness exercise materials for radionuclides in food

The threat to global security from terrorist attack does not solely arise from illicit use of firearms, explosives or weapons of mass destruction. Terrorist threats will inevitably become more subtle as information and expertise is acquired by terrorist groups, and one vulnerable area is food and the food supply chain. Many laboratories, especially in countries with nuclear programmes, are involved in the routine monitoring of foodstuffs, and will be required to respond with increased food monitoring necessary for ensuring food safety and protecting public health after real (or perceived) contamination of food by either accidental or illicit means. This paper examines the needs for reference and performance testing materials that were identified at an international workshop to discuss this matter held at NIST in 2008, and further refined at a follow-up workshop in 2009.

Homogenization of food samples for gamma spectrometry using tetramethylammonium hydroxide and enzymatic digestion

We have developed a method of food sample preparation for gamma spectrometry involving the use of tetramethylammonium hydroxide (TMAH) and/or enzymes such as α-amylase or cellulase for sample homogenization. We demonstrated the effectiveness of this method using food matrices spiked with 60Co, 131I, 134,137Cs, and 241Am radionuclides, homogenized with TMAH (mixed salad, parmesan cheese, and ground beef); enzymes (α-amylase for bread, and cellulase for baked beans); or α-amylase followed by TMAH (cheeseburgers). Procedures were developed which are best compromises between the degree of homogenization, accuracy, speed, and minimizing laboratory equipment contamination. Based on calculated sample biases and z-scores, our results suggest that homogenization using TMAH and enzymes would be a useful method of sample preparation for gamma spectrometry samples during radiological emergencies.

Isotopic analysis of plutonium in foods by inductively-coupled plasma mass spectrometry

Pu isotopes in various foods were detected using a quadrupole ICPMS and Aridus II desolvation nebulizer. The method has ability to detect 239Pu and 240Pu at concentrations of ~52pg/kg (0.12Bq/kg) and ~9.5pg/kg (0.08Bq/kg) as well as 240Pu/239Pu ratio in <8h after receiving the samples. Foods were wet-ashed followed by DGA extraction for eliminating matrix, isobaric, and polyatomic interferences. A UH+ formation rate <10-5 and a 5-fold enhanced sensitivity for Pu was achieved after system optimization.

Analysis of radioactive strontium-90 in food by Čerenkov liquid scintillation counting

A simple liquid scintillation counting method using DGA/TRU resins for removal of matrix/radiometric interferences, Čerenkov counting for measuring 90Y, and EDXRF for quantifying Y recovery was validated for analyzing 90Sr in various foods. Analysis of samples containing energetic β emitters required using TRU resin to avoid false detection and positive bias. Additional 34% increase in Y recovery was obtained by stirring the resin while eluting Y with H2C2O4. The method showed acceptable accuracy (±10%), precision (10%), and detectability (~0.09Bqkg-1).

Rapid detection of enriched uranium in food

We have developed a quadrupole ICP-MS method for detecting sub-picogram quantities of 235U in contaminated foods. Notable features included elimination of the requirement for possessing licensed nuclear materials so that non-radiochemical laboratories may perform this analysis in the event of a large-scale nuclear or radiological emergency calling for high sample surge capacity, elimination of several extremely hazardous reagents in sample analysis e.g. aqua regia and hydrofluoric acid, and the method was developed for applying a moderately priced, and widely used quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS). This method could be quickly implemented at many laboratories to increase emergency response capability.

Computational Approaches on Photon-Attenuation and Coincidence-summing Corrections for the detection of gamma-emitting radionuclides IN foods

Source-based calibration methods used for photon attenuation and coincidence summing corrections are time consuming and require multiple certified standards that match sample geometry with varying densities. Three programs which are capable of simulating a variety of sample geometries, matrix compositions, and sample densities have been examined as alternatives. LabSOCS, ANGLE 3 and GESPECOR are effective at generating efficiency curves for food matrices with a range with different densities. The curves generated have been successfully used to determine activity in food samples.