Method for determining 224Ra in sediment by using pulse ionization chamber emanometer

A method for determining 224Ra in a sediment by using a pulse ionization chamber emanometer, comprising steps of:

• (1) placing a sediment standard sample of 224Ra in a sample tray, connecting the sample tray with an air pump and the pulse ionization chamber emanometer, to form an enclosed test system;
• turning on the air pump and circulating gases in the enclosed test system for at least 5 minutes, such that a radioactive equilibrium between a 220Rn gas released from the sediment standard sample and 224Ra in the sediment standard sample is reached, and performing a first continuous measurement for an activity of Rn in the enclosed test system, to obtain a sum of counting rates of 222Rn and 220Rn, represented by C1, in cpm;
• turning off the air pump, closing inlet valve(s) and outlet valve(s) of the pulse ionization chamber emanometer, and leaving the pulse ionization chamber emanometer to stand for at least 5 minutes, such that 220Rn in the pulse ionization chamber emanometer completely decays and disappears, and performing a second continuous measurement for an activity of Rn in the pulse ionization chamber emanometer, to obtain a counting rate of 222Rn, represented by C2, in cpm;
• and
• calculating a counting rate of 224Ra in the sediment standard sample according to equation 1;
• Cp=Cd=C1−C2 equation 1,
• in equation 1, Cp represents the counting rate of 224Ra in the sediment standard sample, and Cd represents the counting rate of 220Rn in the sediment standard sample;
• (2) repeating step (1) by using different sediment standard samples with a 224Ra activity gradient to obtain counting rates of 224Ra in the different sediment standard samples with the 224Ra activity gradient;
• and
• plotting a standard curve of activities of 224Ra versus counting rates of 224Ra, in which the counting rates of 224Ra in the different sediment standard samples are set as ordinate, and activities of 224Ra in the different sediment standard samples are set as abscissa;
• and
• (3) performing a measurement on a sediment sample to be tested according to step (1) to obtain a counting rate of 224Ra in the sediment sample to be tested, and calculating an activity of 224Ra in the sediment sample to be tested according to the standard curve of activities of 224Ra versus counting rates of 224Ra obtained in step (2).