Bragg Curve


Stage, camera holder, source holder, polonium, 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: check
    7. Color Map: Hot
  2. Mount the MiniPix EDU camera and polonium on the Stage.
  3. Keep a distance of 1.5 cm between the camera and source and click on the play button to collect data.
  4. Next, shift the source by 0.3 cm away from the camera and collect the data again. Repeat the process until the energy peak stops showing up.
  5. Make a table for distance (d) and kinetic energy of alpha particles (Ek) (Table 1)


  1. We can calculate the linear stopping power (S1) of air using the three-point numeric derivative of kinetic energy (Ek) with respect to distance traveled (d).

    where h = 0.3,
  2. The distance (d), kinetic energy (Ek), and stopping power (S1) is shown in table 1 and figure 1 shows the distance vs stopping power

    Table 1. Comparison of the kinetic energy of alpha particles (Ek) and stopping power (S1) with distance 

    Figure 1. Bragg curve of stopping power of air on alpha particles

  3. We stopped the measurement at a distance of 4.2 cm because the energy histogram started losing its Gaussian shape.


  1. From the table, we observe that the stopping power is increasing with distance. 
  2. Initially, the alpha particle loses its energy in the range of 1000 keV to 1150 keV which jumps to ~1500 keV and it loses ~2000 keV for the last displacement in the experiment.
  3. Our curve corresponds to the part of Bragg Curve (Fig. 2). Alpha particle loses most of its energy shortly before it stops.

    Figure 2. The typical shape of the Bragg curve

  4. The reason we cannot observe the whole Bragg Curve is that our source is not mono-energetic. This ability of heavy charged particles to pass maximum energy at the very end of its range is utilized in proton or hadron therapy.

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