IB Physics IA idea · Nuclear and modern physics
IB Physics IA idea: detect natural radioactivity in salt substitute
A tiny fraction of potassium is radioactive. A shaker of salt substitute can be detected with a Geiger counter.
These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.
Example research question
How does the net count rate over a Geiger tube depend on the mass of potassium chloride salt substitute in a flat tray, from 0 to 200 g in eight steps counted for 5 minutes each, and does it level off?
Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Physics IA guide.
Variables
- You change
- mass of potassium chloride in a flat container, 0 to 200 g in 8 steps
- You measure
- net count rate, 0 to 50 counts per s
- You keep the same
- container geometry
- distance to the tube
- background subtraction
- counting time
Method
Place potassium chloride (a sold salt substitute) in a flat tray over a Geiger tube and count for 5 minutes at each mass. Subtract the background.
Data analysis
Plot net count rate against mass; it should rise and then saturate as beta particles are absorbed within the salt. Fit a saturating model and compare the saturation depth with the beta range.
How it works
You change Mass of potassium chloride (g) and measure Net count rate (counts s⁻¹) in Salt over Geiger tube, keeping Tray shape, Counting time, Background rate, Tube position the same. Expect a graph of Net count rate / s⁻¹ against Mass of KCl / g: Deep layers add little: the beta particles are absorbed in the salt.
Make it yours
Measure through different shielding or compare with other potassium-rich foods.
Extended Essay angle
Estimate the specific activity of K-40 and compare with the accepted value using a calibrated detector model.
Safety
Take care with: radiation.
Low-activity consumer product; handle as food; wash hands; teacher approval.
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