Radioactive Wastes

Part 3: Isotope Half-Lives

In this part of the module, we will use other sites on the World Wide Web. Remember that you can return to this page from a remote site by using the BACK button on your browser.

1. The Environmental Health and Safety office at UC Santa Cruz has a useful online decay calculator for six specific isotopes. Use it to calculate the decay of 500 milliCuries (mCi) of phosphorus-32 from your choice of "reference date" to today. Record the output in your worksheet: current amount, lambda value, and time elapsed.
2. Calculate the half-life for ³²p.
3. How long does it take for 500 mCi of ³²p to decay below 1 microCurie (uCi)? Plot the decay function for ³²p over this length of time. How does this decay time compare with the Duke EPD guideline of 10 half-lives?.
4. Repeat Steps 1-3 for 500 mCi of iodine-125 (¹²⁵I).
5. Iodine-131 is not one of the isotopes in the UCSC decay calculator. To find its half-life (and more about it than you ever wanted to know), explore the Table of the Nuclides page at Brookhaven National Lab. Record your findings, and repeat Step 3 for ¹³¹I.

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