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  • Radioactive sequence of elements (qualitative).

Topics:  Radioactive decay, radioactivity, exponential rate, radioactive sequence.

Pre-requisite skills:  Understanding of basic radioactivity.

Approximate completion time:  Under an hour.

Provide sufficient detail to verify that the assignment was completed in a meaningful manner.

Applet by Yevgeniy Miretskiy

This applet demonstrates various radioactive sequences.  There are four sequences available to examine.  In this assignment, we will examine the Pu241 sequence.

1.  Select Pu241 in the upper portion of the applet.  Notice that only six isotopes are shown.

(a)  These are not the only isotopes that appear in the Pu241 sequence.  The entire sequence is shown in the display on the right side of the applet, in the order in which they appear in the sequence.  (You can also view the sequence by pressing the "Sequence Info" button.)   Describe why the omission of these isotopes is reasonable.

(b) The vertical axis plots the number of atoms that appear at any given time.  The actual data represented here is also tabulated in the window on the right-side of the applet when running.  At the start of the sequence, which isotope appears, and how many of the isotopes appear?

2.   Set the time step to 5 and run the applet until all of the original isotope have decayed.

(a)  Since Np237 is a daughter product of Am241, why is there almost as many Np237 isotopes as Am241 isotopes?  (Hint:  Look at the half-lives of both isotopes.)

3.  Set the time step to 100 (to speed up the decay process) and run the applet further until all of the Am241 isotope has decayed.

(a)  Why was it desirable to increase the time step?

(b)  Which isotope is now most abundant?

4. Once all of the Am241 has decayed, the number of Np237 atoms appears to change very slowly.  Describe why this is occuring.

Helpful Resources

  1. Isotopes by Physics 2000.
  2. Table of the Nuclides by Jonghwa Chong
  3. Chart of the Nuclides by Jun-ichi Katakura
  4. Tables of Nuclear Data by Nuclear Data Center
  5. Radioactive Decay by Angel Franco Garcia
  6. Law of Radioactive Decay by Walter Fendt
  7. Radioactivity Unit Converter by Department of Environmental Health and Safety

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