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not remain at a constant •ght after being dried at 105 •°C for 2 hr and the n <br />exposed to the atmosphere before and during counting Other rad~oactivitie s <br />(such as some chemical forms of radioiodine) may a lso be lost during the sample <br />evaporation and drying at 105 °C. Those types of water samples need to be heate d <br />to a dull red heat for a few minutes to convert the salts to oxides. Sampl e <br />weights are then usually sufficiently stable to gi ve consistent counting rates. <br />and a correct counting efficiency can then be assigned. Some radioactivities. <br />such as the cesium radioisotopes, may be lost when samples are heated to a dull <br />red color. Such losses are limitations of the test method. <br />1.9 This method provides a rapid screening measurement to indicate whethe r <br />spec~f~c analyses are required. When the gross al pha particle activity exceeds <br />5 pCi/L. the same or an equivalent sample shall be analyzed for alpha-emitting <br />radium isotopes (Method 9315) or an alternative me asurement of radium-226 alpha <br />emission (Standard Methods for the Examination of Water and Wastewater. 15t h <br />edition. Method 705 or 706, respectively). Gross beta particle emission s <br />exceeding 15 pCi/L in a sample shall be analyzed for strontium-89 and cesium-13 4 <br />(Standard Methods for the Examination of Water and Wastewater, 15th edition <br />Methods 704 and 709. respectively). [f gross beta activity exceeds 50 pCi/L, th e <br />identity of the major radioactive constituents must be evaluated and th e <br />appropriate organ and total body doses determined. <br />2.0 SUMMARY OF METHOD <br />2 1 An aliquot of a preserved water sample is evaporated to a small volum e <br />and transferred quantitatively to a tared 2-in. stainless steel countin g <br />planchet. The sample residue is dried to constant weight. reweighed to determin e <br />dry residue weight, and then counted for alpha and/or beta rad~oactiv~ty. <br />2.2 Counting efficiencies for both alpha and beta particle activities ar e <br />selected according to the amount of sample solids from counting efficiency vs. <br />sample solids standard curves. <br />3.0 INTERFERENCES <br />3.1 Moisture absorbed by the sample residue is an interference because i t <br />obstructs counting and self-absorption characteris tics. If a sample is counted <br />in an internal proportional counter, static charge on the sample residue ca n <br />cause erratic counting. thereby preventing an accurate count. <br />3.2 Nonuniformity of the sample residue in counting planchet interfere s <br />with the accuracy and precision of the method. <br />3.3 Sample density on the planchet area should be not more than 10 mg/cm Z <br />for gross alpha and not more than 20 mg/cm z for gross beta. <br />9310 - 2 <br />CD-ROM Revision 0 <br />Date September 1986 <br />