Alpha Particles being Blocked by a Piece of Paper


Stage, camera holder, source holder, polonium-210 , paper, 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: 100
    5. Exposure: 1 s
    6. Sum: uncheck
    7. Color Map: Hot
  2. Mount the MiniPix EDU camera and polonium on the stage.
  3. Keep the camera and the source 1.5 cm apart and click on the play button.
  4. During the experiment cover half of the camera sensor with paper, as shown in figure 1.
    CAUTION: Make sure that paper does not touch the sensor of the camera

    Figure 1. Sticky note being used to cover half of the camera sensor.


  1. Initially, we observe that the frame is full of alpha particles (Fig. 2).

    Figure 2. The alpha particles from Po-210 being detected by the camera

  2. After covering half of the camera sensor with paper, the alpha particles disappeared from the half-covered frame showing that the alpha particles can be blocked by a piece of paper (Fig. 3).

    Figure 3. The alpha particles being blocked by a piece of paper


  1. The alpha particles being the heaviest, lose the energy quickly and thus have a very small linear range which decreases after a denser material like paper comes in the way.
  2. Although, we still observe the gamma photons on the frame where the alpha particles have disappeared. This is because gamma photons have more penetrating power because they have no charge and thus do not interact with the matter as much as other particles.
  3. Sometimes, if the piece of paper is thin enough and the source and camera are very close, the alpha particles can pierce through the paper too. Try using different materials like polythene bags, tissue paper, paper napkin, etc.

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