I was recently re‐calculating laboratory results for Ra‐228 from a laboratory using a slightly modified version of Method 9320, using the calculation on page 5. Using this equation, I was not able to duplicate the results that the laboratory reported. However, when I multiplied the t1 and t3 time by the decay constant, I was able to duplicate the results.
The equation in older versions of SW-846 Method 9320 is misprinted. The error has been fixed in the Update V version of the method, which can be found at www.epa.gov/sites/production/files/2015-12/documents/9320.pdf. Any decay equation requires the incorporation of the decay constant, lambda, which is ln2/half-life.
Other category: 9000 series, Inorganic