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Significance and Use
This test method measures the presence of uranium and thorium in soil that occurs naturally and as a result of contamination from nuclear operations and uranium ore processing. The reporting detection levels (RDLs) of total uranium and thorium are well below the normal background in soil. The normal background level for uranium is between 3 and 5 μg/g in most geographic areas and slightly higher for thorium. The 235U enrichment is also measured from an initial sample pass through the instrument. The other less abundant uranium isotopes (234U and 236U) are measured down to a typical soil background level after sample concentration and a second sample analysis. This allows for calculation of individual isotopic uranium and total uranium activity. The majority of the uranium activity results from 234U and 238U.
1.1 This test method covers the measurement of total uranium (U) and thorium (Th) concentrations in soils, as well as the determination of the isotopic weight percentages of 234U, 235U, 236U, and 238U, thereby allowing for the calculation of individual isotopic uranium activity or total uranium activity. This inductively coupled plasma-mass spectroscopy (ICP-MS) method is intended as an alternative analysis to methods such as alpha spectroscopy or thermal ionization mass spectroscopy (TIMS). Also, while this test method covers only those isotopes listed above, the instrumental technique may be expanded to cover other long-lived radioisotopes since the preparation technique includes the preconcentration of the actinide series of elements. The resultant sample volume can be further reduced for introduction into the ICP-MS via an electrothermal vaporization (ETV) unit or other sample introduction device, even though the standard peristaltic pump introduction is applied for this test method. The sample preparation removes organics and silica from the soil by use of a high temperature furnace and hydrofluoric acid digestion. Thus, this test method can allow for sample variability of both organic and silica content. This test method is also described in ASTM STP 1291. Since this test method using quadrupole ICP-MS was approved, advances have been made in ICP-MS technology in terms of improved sensitivity and lower instrument background as well as the use of collision or reaction cells (or both) and sector field mass spectrometers with single and multiple detectors. These advances should allow this test method to be performed more effectively but it is the user’s responsibility to verify performance.
1.2 The analysis is performed after an initial drying and grinding sample preparation process, and the results are reported on a dry weight basis. The sample preparation technique used incorporates into the sample any rocks and organic material present in the soil. The method of sample preparation applied differs from other techniques, such as those found in Practice C 999
1.3 The values stated in SI units are to be regarded as standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
C859 Terminology Relating to Nuclear Materials
C998 Practice for Sampling Surface Soil for Radionuclides
C999 Practice for Soil Sample Preparation for the Determination of Radionuclides
C1255 Test Method for Analysis of Uranium and Thorium in Soils by Energy Dispersive X-Ray Fluorescence Spectroscopy
D420 Guide to Site Characterization for Engineering Design and Construction Purposes
D1193 Specification for Reagent Water
D1452 Practice for Soil Exploration and Sampling by Auger Borings
D1586 Test Method for Penetration Test (SPT) and Split-Barrel Sampling of Soils
D1587 Practice for Thin-Walled Tube Sampling of Soils for Geotechnical Purposes
D2113 Practice for Rock Core Drilling and Sampling of Rock for Site Investigation
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D3550 Practice for Thick Wall, Ring-Lined, Split Barrel, Drive Sampling of Soils
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E305 Practice for Establishing and Controlling Atomic Emission Spectrochemical Analytical Curves
E456 Terminology Relating to Quality and Statistics
E876 Practice for Use of Statistics in the Evaluation of Spectrometric Data
E882 Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
U.S. EPA StandardMethod6020 SW-846, Inductively Coupled Plasma-Mass Spectrometry
ICS Number Code 13.080.10 (Chemical characteristics of soil)
UNSPSC Code 11111501(Soil)