Significance and Use 5.1 Radium is one of the most radiotoxic elements. Its isotope of mass 226 is the most hazardous because of its long half-life. The isotopes 223 and 224, although not as hazardous, are of some concern in appraising the quality of water. 5.2 The alpha-particle-emitting isotopes of radium other than that of mass 226 may be determined by difference if radium-226 is measured separately, such as by Test Method D3454. Note that one finds 226Ra and 223Ra together in variable proportions (5, 6), but 224Ra does not normally occur with them. Thus, 223Ra often may be determined by simply subtracting the 226Ra content from the total: and if 226Ra and 223Ra are low, 224Ra may be determined directly. The determination of a single isotope in a mixture is less precise than if it occurred alone.Scope 1.1 This test method covers the separation of dissolved radium from water for the purpose of measuring its radioactivity. Although all radium isotopes are separated, the test method is limited to alpha-particle-emitting isotopes by choice of radiation detector. The most important of these radioisotopes are 223Ra, 224Ra, and 226Ra. The lower limit of concentration to which this test method is applicable is 3.7 × 10-2 Bq/L (1 pCi/L). 1.2 This test method may be used for absolute measurements by calibrating with a suitable alpha-emitting radioisotope such as 226 Ra, or for relative methods by comparing measurements with each other. Mixtures of radium isotopes may be reported as equivalent 226Ra. Information is also provided from which the relative contributions of radium isotopes may be calculated. 1.3 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. For a specific precautionary statement, see Section 9.
