Measuring the Radioactivity of Water The Activities of Subcommittee D19.04 on Methods of Radiochemical Analysis
The development of many methods for the analysis of radioactivity stems from the U.S. Manhattan Project during World War II more than 60 years ago. Concern for the potential health effects of both man-made and natural radioactivity in the environment has driven the need for environmental radioactivity methods. For many years since World War II, scientists from various nuclear facilities, and now U.S. national laboratories, had their favorite method of analysis and typically shared such information on a very restricted basis.
Although some proprietary radiochemical methods still exist, the approach today is for an open forum, where methods and technology are developed and shared collaboratively. ASTM International was founded on this concept and Subcommittee D19.04 on Methods of Radiochemical Analysis has more than 40 years of experience in establishing radiochemical methods for the measurement of radioactivity in water.
The D19.04 radiochemical methods published in Volume 11.02 of the Annual Book of ASTM Standards are a blend of methods based on the classical radiochemical separations of the 1950s and the latest radionuclide separation techniques and instrumentation of today. In some cases, Subcommittee D19.04 has had to archive methods that have become outdated because the stated instrumentation is no longer available or an improved method has become the method of choice.
Subcommittee D19.04 is a very active group, with over 50 members from industry, universities, and commercial and government radioanalytical laboratories. The subcommittee is divided into five custodial task groups. The task groups include those for heavy elements, activation and fission products, measurement of radioactivity, rapid methods for radiological measurements and low-level radionuclides by mass spectrometry. The latter two task groups were recently formed in response to industry and homeland security needs.
Currently, the subcommittee is actively developing seven additional standards for 210Pb, isotopic radium, rapid screening method for gross alpha/beta activity, isotopes of iodine including 129I, 89/90Sr in water and a rapid 90Sr method for vegetation. After a major effort, a new practice is being balloted that will establish calibration and operational quality control criteria for laboratory nuclear instrumentation. This practice should establish consistent and sensible criteria for the nuclear industry and radioanalytical laboratories. Currently, an interlaboratory collaborative study has been conducted on the proposed standard on the measurement of 210Pb in water.
Subcommittee D19.04 also recognizes its responsibility to work with relevant U.S. federal agencies, e.g., the Environmental Protection Agency, to develop methods that support regulations promulgated by those agencies. Such a working relationship is described in US Public Law 104-113, the National Technology Transfer and Advancement Act. The subcommittee has had discussions with EPA Office of Water personnel over the last several years to work toward establishing such a mutually beneficial working relationship.
Given the value of its members’ time, the subcommittee has strived to make the most efficient use of this important asset. Advances in the ASTM International online balloting system has helped to speed the development of standards. Also, the subcommittee has moved to utilize professional meetings outside of ASTM Committee Weeks, e-mail and conference calls to use members’ time most efficiently.
In recognition of the need for radioactivity measurements not being limited to Committee D19, several D19.04 members are active in other ASTM committees such as C26 on Nuclear Fuel Cycle and E54 on Homeland Security Applications. Members of D19.04 also monitor the standards development activities of organizations such as Standard Methods for the Examination of Water and Wastewater and relevant International Organization for Standardization (ISO) technical committees.
The conduct of interlaboratory collaborative studies for D19.04 methods per ASTM standard D 2777, Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water, is very important for method validation and for estimating the expected bias and precision of a method. The resources needed to conduct such studies are extremely extensive and expensive. Because most radiochemical methods require sample preparation, extensive chemical separations by various means and long radiation emission measurement durations, laboratories engaged in the studies must allocate dedicated facilities and more than a week of analyst time. Obtaining certified radioactive standards and preparing and distributing the test samples in the study are expensive (costing thousands of dollars) and require the unique services of highly qualified radioactive source producers. In spite of these challenges, the radioanalytical laboratory community understands the importance of recognized voluntary consensus standards and supports the conduct of D19.04 collaborative studies.
The scopes and status of the five task groups are provided below.
D19.04.01 on Heavy Elements
Ann Mullin, chair, and Sherrod Kyle, vice chair
The Task Group on Heavy Elements currently maintains seven active methods with two new methods set to undergo interlaboratory collaborative studies. Standard methods for which this group is responsible include isotopic plutonium and isotopic uranium, as well as trace uranium by pulsed-laser phosphorimetry and uranium in drinking water by high-resolution alpha-liquid-scintillation spectrometry. Also covered by this group are 226Ra and 222Rn in drinking water and total alpha-particle emitting isotopes of radium in water.
An interlaboratory collaborative study for 210Pb in water was conducted during the summer and fall of 2006. Plans for an interlaboratory collaborative study for the analysis of the individual alpha emitting isotopes of radium by alpha spectrometry are nearing completion. This study is scheduled for this year. Being considered for future development are methods for 228Ra and 241Am in water.
D19.04.02 on Activation and Fission Products
Robert Shannon, chair, and Stan Morton, vice chair
The Task Group on Activation and Fission Products sadly saw the passing of long-standing chair Frank Krowzack this past year. Recent task group accomplishments include final approval of D 7168, Test Method for 99Tc in Water by Solid Phase Extraction Disk. Single operator testing is under way for an elegant method for the determination of 89Sr and 90Sr in water. The technique combines the efficiency and specificity of extraction chromatography separations with the unique energy discrimination possible with Čerenkov radiation detection by liquid scintillation spectrometry. The method will address a weak point in classic methods for 89Sr and 90Sr since it can discriminate between the two beta-emitting radioisotopes even when they are present in samples at extreme ratios. Additional methods maintained by the task group include those for tritium in drinking water, 90Sr (by extraction chromatography), and low-level radioiodine and radioactive iron in water.
D19.04.03 on Measurement of Radioactivity
Donivan Porterfield, chair, and Carolyn Wong, vice chair
Linking most radiochemical methods is the nuclear counting instrumentation that acquires quantitative radionuclide data. The methods developed by the Task Group on Measurement of Radioactivity provide valuable support to the methods of other task groups that require chemical separations in advance of counting. Also supporting the methods of other task groups is the new D 7282, Practice for Setup, Calibration, and Quality Control of Instruments Used for Radioactivity Measurements.
The work of this task group also addresses methods that require no chemical separations in advance of counting. An example of such is the new standard D 7283, Test Method for Alpha- and Beta-Particle Radioactivity in Water by Liquid Scintillation Counting. This method also highlights the task group’s ongoing need to address continuing improvements in instrumentation performance and relies on the ability of recent liquid scintillation counters to distinguish detected alpha and beta decay events.
New types of nuclear detector materials open up the need for new or revised methods to address their potential. Examples of such materials for detection of gamma-ray photons include cadmium telluride, cadmium zinc telluride, and lanthanum halides (bromide and chloride). CT and CZT detectors provide good spectral resolution without the need for cryogenic cooling. Lanthanum halide detectors provide better spectral resolution than sodium iodide and larger detector volumes than CT and CZT detectors.
Beyond advances in radiation detector materials there are also improvements in the manner in which data is communicated and analyzed. Not too many years ago, interfacing of nuclear counting instrumentation to computers required the use of proprietary vendor interfaces and specialized software. Most current nuclear counting instrumentation can be quickly connected to computers using a common interface such as USB cables. The increasing power of computers allows more complex analysis of multi-channel data to improve the quality and speed with which results can be obtained. The power of data acquisition and analysis opens up the potential for data approaches such as list-mode time-stamp for spectral data.
D19.04.04 on Rapid Methods for Radiological Measurements
Douglas Van Cleef, chair, and David Burns, vice chair
The Task Group on Rapid Methods for Radiological Measurements was formed in 2004 for the purpose of developing, testing and disseminating analytic methods for use when time is of the essence, such as following a radiological emergency. The task group focuses on guides, practices and methods for a variety of media and analytes listed as priorities by state and federal agencies with responsibilities for emergency response. The task group members represent numerous national laboratories and commercial interests, and the development work is conducted in cooperation with the national laboratories.
Activities for this task group include the finalization of guides for existing field instrumentation to influence emergency response decisions and the rapid screening of vegetation for 90sr contamination and a practice for the rapid screening of alpha- and beta-particle radioactivity in water by liquid scintillation counting.
D19.04.05 on Measurement of Radioactivity and Low-Level Radionuclides by Mass Spectrometry
Donna Beals, chair, and Linda Nichols, vice chair
The detection of radionuclides in water often requires a chemical separation of the element of interest followed by counting alpha, beta or photon emissions of the decaying radionuclide or isotope of interest. In recent years, the detection limit routinely achievable and the availability of mass spectrometers has improved to the point that many long-lived radionuclides (with a half-life greater than 100-1,000 years) are now being analyzed by mass spectrometry rather than by traditional decay particle emission counting methods. Although many standards exist on the use of mass spectrometry as a technique for measuring isotopes, ASTM International currently has no standards pertaining to the use of mass spectrometry to measure trace levels of radionuclides in water.
Subcommittee C26.05 on Methods of Test for the Nuclear Fuel Cycle has a few methods for the analysis of uranium, thorium and 99Tc in soil and urine by inductively coupled plasma mass spectrometers to support bioassay and remediation efforts. Subcommittee D19.05 on Trace Metals in Water uses ICP-MS to quantify metals in water; however, this method is not applicable to the isotopic analysis of radionuclides at the required detection limits. Therefore, it was decided to form this newest task group in Subcommittee D19.04. D19.04.05 will primarily focus on methods utilizing ICP-MS to quantify activities of various radionuclides in water. The methods developed in this task group will focus on the analysis of water and other matrices to support environmental monitoring (to meet EPA and other requirements) and homeland security applications. No efforts of this task group should overlap with those of C26.05, but rather will complement them so that ASTM provides guidance for a wide range of mass spectrometry applications to the analysis of radionuclides.
Of special note not presented above is the technical, time and financial support of the commercial industry, private and government laboratories and government agencies in the ongoing activities of D19.04. The subcommittee truly appreciates the past and current support, without which existing and future advances in method development and validation would not be possible. Such employer support has allowed a large group of D19.04 members to work in both a friendly and professional manner to effectively develop a body of methods that are valued and used by peers in both the United States and internationally. //