Effect of Collimator on the Detected Energy of Alpha Particles


Stage, camera holder, source holder, collimator, polonium-210, Minipix-EDU


  1. Launch the Pixet Basic software and modify settings to the following:
    1. Min Level: 0
    2. Max Level: 100
    3. Measurement Mode: Tracking
    4. Frames: 600
    5. Exposure: 1 s
    6. Sum: check
    7. Color Map: Hot
  2. Mount the MiniPix EDU camera and polonium on the Stage. Make sure to put polonium in the rear slot and then insert the collimator, as shown in figure 1.

    Figure 1. The setup of  polonium, collimator, and camera on the stage.
  3. Set the distance to ~2.5 cm and click on the play button. Caution: make sure that the collimator does not touch the sensor.
  4. Save the energy histogram as ASCII Vertical (*.vtxt) format (explained in Introduction of Pixet Basic Software).
  5. Repeat the same experiment without the collimator and make sure that the distance does not change and save the histogram for this as well.
  6. Now export the results into excel (explained in Introduction of Pixet Basic Software) and plot the curve between energy and counts of alpha particles.


  1. Both the graphs have a similar pattern, with the peak almost at the same point. But once you overlay the two graphs, we observe that the experiment with the collimator has a much smaller peak (Fig. 2).

    Figure 2. The alpha energy peak from Po-210 both with and without collimator

  2. This is because the radiation from the source is a divergent beam and a lot of energy is absorbed or blocked by the collimator itself.
  3. Another observation is the decrease in the counts of low energy particles in the experiment with the collimator (Fig. 2). Or we can say that the peak is wider without the collimator


  1. The experiment without a collimator has many alpha particles hitting the edges of the camera and thus does not register all of their energy.
  2. This increases the count of low energy particles. 
  3. The collimation decreases the particles striking the edges of the camera and thus have a flattening curve at lower energy.

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