Episode 512: Nuclear equations

Now that your students are familiar with different types of radiation, you can look at the processes by which they are emitted.

Lesson Summary

• 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.

Episode 512-1: Nuclide notation (Word, 36 KB)

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.

Episode 512-2: Decay processes (Word, 53 KB)

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

Episode 512-3: Practice with nuclear equations (Word, 66 KB)

The more unusual decay processes (positron emission, neutron emission, electron capture) could be included, and students challenged to write them as nuclear equations.