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During alpha decay, the atomic number decreases by 2, e.g., from 106 (Seaborgium) to 104 (Rutherfordium). Experimental measurements show that the combined mass of the resulting daughter nucleus and the emitted alpha particle is slightly less than the mass of the original (parent) nucleus. According to Einstein’s equation, E=mc15, this reduction in mass is released as energy. The emitted alpha particle carries this energy in kinetic form, traveling at high speed. Despite its high energy, it can be easily stopped by a simple barrier such as a sheet of paper or even human skin. 

Procedure

1. Place down a short strip of tape and measure out 0cm, 0.5cm, 1cm, 1.5cm, and 2cm. Mark those points using a pen.

2. Place your alpha source at the 0cm point making sure it's placed upright or facing your Geiger counter.

3. Put the Geiger counter in a comfortable spot. If your counter has a built-in radiation source, then put it further away to reduce error.

4. Record the background activity before starting.

5. After, place the counter on the tape, 0.5cm from the radiation source and begin measuring.

6. Wait until the counter is stable and record the counts-per-minute, you only need to perform 1 trial.

7. Repeat steps 5 and 6 while moving your counter to the other points.

8. Make sure you record all your data in the spreadsheet, observe any noticeable patterns.

Questions:

1. At what distance did the alpha radiation count equal that of the background count?

2. What is the charge of the alpha particle? How do you know this?

3. List several reasons why the alpha particle does not travel more than several centimeters.

Optional:

1. What is the mass of an alpha particle compared to an electron?

2. Using the "Chart of Nuclides," what distinguishes the daughter isotopes and the particles emitted from each other?

To access data from our own trials, click here.