Liquid Radioactive Waste Analysis

For P-32 and I-125
Click below for printable versions of the charts to use to estimate the amount of P-32 or I-125 in a full RPO-issued liquid waste container by using a portable survey meter.

• How to Estimate Your P-32  
• How to Estimate Your I-125  

For other radionuclides, or partially full containers
The best way to determine the amount of radioactive material in liquid waste is to count a 1 milliliter sample in a liquid scintillation or gamma counter when the jug is ready to be collected for disposal. Follow these steps:

1. Count the sample for 1 to 10 minutes.
2. Obtain the disintegration rate (dpm) of the sample by dividing the obtained count rate (cpm) by the instrument counting efficiency for that radionuclide.
3. Correct this result for the total volume of the container, by multiplying the result by the volume of the container divided by the volume of the sample. A full container holds approximately 9,500 milliliters. So, for a jug filled to the fill line, and a 1 millilter sample, multiply the result by 9,500.
4. Convert the disintegration rate to mCi units, where 1 mCi = 2.22 x 10⁹ dpm.

For example, if a sample of tritium waste counted in an LSC with an efficiency of 50% had 10,000 net cpm, there would be 20,000 dpm of tritium in the sample.

sample dpm = 10000cpm / 0.50 = 20000 dpm

The jug would then have a total of 1.9 x 10⁸ dpm of tritium.

jug dpm = sample dpm x (jug mL / sample mL)
jug dpm = 20000 dpm x (9500 mL / 1 mL)
jug dpm = 1.9 x 10⁸ dpm

Converting to milliCuries, we have a total of 0.086 mCi of tritium in the jug.

jug mCi = (jug dpm) / (2.22 x 10⁹ dpm / mCi)
jug mCi = 0.086 mCi