- 标准号：ASTM C1345-1996(2001)
- 发布日期：1996
- 英文题名：Standard Test Method for Analysis of Total and Isotopic Uranium and Total Thorium in Soils by Inductively Coupled Plasma-Mass Spectrometry
- 英文主题词：inductively coupled plasma-mass spectrometry (ICP-MS) ; isotopic ratio ; soil ; thorium ; uranium
- 标准状态：现行
- 发布单位：US-ASTM
- 国际标准分类号：13.080.10 (Chemical characteristics of soil)
- 载体形态：12P.;A4
- 中国标准分类号：B11
- 国别：美国材料与试验协会
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 x03BC;g/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.
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 C999, which involve simply tumbling and sieving the sample; however, the user may select whichever technique is most appropriate to their needs.
1.3 A linear calibration is performed for total uranium and thorium over a concentration range from 5 to 5000 181g/L, using approximately 6 points. As with the data presented, it is suggested that the increments between points be less than or equal to a factor of ten. With a sample dilution factor of 200 resulting from the preparation, this equates to a concentration range in the samples from 1 to 1000 181g/g. For those samples estimated to be above that range by initial activity screening, a smaller aliquot is taken to a dilution of 1000, thereby extending the range to 5000 181g/g. It is important to note that the concentration measured directly from this calibration is the concentration of 238U. The standard values are adjusted for abundance and the abundances in the instrument database are modified to eliminate any automatic correction, as discussed further in the appropriate sections. The calibration range can be changed based on the needs of the user and the expected variation among samples.
1.4 Corrections to the measured isotopic ratios for mass bias effects are made by determining and applying a mass bias factor (see 13.3.1). This can be performed for ea......