Nuclear Decay Topic 7.2

Forces in the nucleus

The repulsive force between protons in the nucleus The Coulomb Force The repulsive force between protons in the nucleus + +

The Strong Force The nucleons (protons and neutrons) in the nucleus are bound together by the strong nuclear force

The Strong Force acts over short distance (10-15 m) acts only between adjacent particles in the nucleus What happens when the size of the nucleus approaches 10-15 m?

Unstable nuclei Example: Uranium 235 Is it predictable? To become stable, an unstable nuclei emits a particle We say the atom has decayed The decay of an unstable nucleus is random. We know it’s going to happen, but we can’t say when! It is spontaneous. It cannot be affected by temperature/pressure etc.

Becquerels (Bq) The amount of radioactivity given out by a substance is measured in Becquerels. One becquerel is one particle emitted per second. Henri Becquerel 1852-1908

Detection Particles can be detected by photographic film Particles can also be detected (and counted) by a Geiger- Müller tube (GM tube) connected to a counter

Nuclear Decay Activity

Procedure: Count your nuclei (candy). Write that number in the data table under the heading “Number of Radioactive Nuclei.” In the column marked “Prediction for Next Toss” write the number of radioactive nuclei you think you will have with your next toss. (Radioactive nuclei will be those candies with the marked side down.)

Procedure: 3. After the assigned amount of time (5s/10s/15s), place your “nuclei” in a paper cup, cover and shake the cup. Pour the “nuclei” onto your paper. 4.Separate the “nuclei” into two piles, one with the marked side up and the other with the marked side down.

Procedure: Count the number of “nuclei” in each pile. On your data table, record the number of “radioactive nuclei” candies with the marked side down. Predict how many radioactive “nuclei” you will have after the next toss.

Procedure: 7. Return only the radioactive “nuclei” to your paper cup. (those with the marked side down) 8.Decide what to do with the “decayed nuclei,” (those with the marked side up)

Procedure: 9. Count to the appropriate time interval and continue this process until there are no radioactive “nuclei” left. 10. Graph your results. What kind of graph do you expect?