Episode 512: Nuclear equations
Lesson for 16-19
- Activity time 70 minutes
- Level Advanced
Now that your students are familiar with different types of radiation, you can look at the processes by which they are emitted.
- Discussion: Nuclide notation and N – Z plot (10 minutes)
- Student Questions: Practice with notation (10 minutes)
- Worked Examples: Equations for alpha, beta and gamma decay (20 minutes)
- Student Questions: Practice with nuclear equations (30 minutes)
Discussion: Nuclide notation
Revise nuclide notation: AZX
Discuss how A(mass or nucleon number), Z (charge or atomic number) and N(neutron number are related):
A = Z + N.
Discuss isotopes (common examples: H, D and T, U-235 and U-238, C-14 and C-12).
Set the task of finding out the name for nuclides having the same A but different Z (isobars), and the same N but different Z (isotones).
Show an N-Z plot (Segrè plot).
Student questions: Practice with notation
Set some simple questions involving nuclide notation.
Grid showing change in A and Z with different emissions.
Worked examples: Equations for alpha, beta and gamma decay
Nuclear decay processes can be represented by nuclear equations. The word equation implies that the two sides of the equation must
balance in some way.
You could give examples of equations for the sources used in school and college labs.
α sources are americium-241, 24195Am
24195Am → 23793Np + 42He
β - sources are strontium-90, 9038Sr
9038Sr → 9039Np + 0-1e
The underlying process is:
n → p + e- + n
Here, n is an antineutrino. Your specification may require you to explain why this is needed to balance the equation.
You can translate n → p + e- + n into the AZ notation:
10n → 11H + 0-1e
γ sources are cobalt-60, 6027Co. The γ radiation comes from the radioactive daughter 6028Ni of the β decay of the 6027Co.
The 6028Ni is formed in an
excited state and so almost immediately emits a γ ray. They are only emitted after an α or β decay, and all such γ rays have a well-defined energy. (So a cobalt-60 source which is a pure gamma emitter must be designed so that betas are not emitted. How? – (by encasing in metal which is thick enough to absorb the betas but which still allows gammas to escape.)
Student questions: Practice with nuclear equations
The more unusual decay processes (positron emission, neutron emission, electron capture) could be included, and students challenged to write them as nuclear equations.