1. Physics 12 Nuclear Physics 3 – Radio Activity Mr. Jean

2. The plan: Video clip of the day Nuclear Stability curve Decay Models

3. Why radio active & Why not: http://www.youtube.com/watch?v=H8Yd2T 9MQBUhttp://www.youtube.com/watch?v=H8Yd2T 9MQBU

4. As the number of protons increase, the number of neutrons increases. As the nucleus gets bigger, we soon find that the nuclei have more neutrons than protons. For some reason, certain combinations of neutrons and protons are more stable than others. –For example: C-12 is stable, but C-14 is radioactive. The force that keeps the nucleus together, that acts between protons and neutrons is called the nuclear force. Sometimes called Nuclear strong force.

5. To sum it up: The strong nuclear force is enormously stronger than the electromagnetic force. The strong nuclear force has a much smaller effective range than does the electromagnetic force. Neutrons are required in the mix of protons for the strong force to work properly.

6. Composition of Matter All of matter is composed of at least three fundamental particles (approximations): ParticleFig.SymMassChargeSize The mass of the proton and neutron are close, but they are about 1840 times the mass of an electron. Electron e - 9.11 x 10 -31 kg-1.6 x 10 -19 C  Proton p 1.673 x 10 -27 kg +1.6 x 10 -19 C 3 fm Neutron n 1.675 x 10 -31 kg 0 3 fm

7. Atomic Mass Unit, u One atomic mass unit (1 u) is equal to one- twelfth of the mass of the most abundant form of the carbon atom--carbon-12. Atomic mass unit: 1 u = 1.6606 x 10 -27 kg Common atomic masses: Proton: 1.007276 u Neutron: 1.008665 u Electron: 0.00055 uHydrogen: 1.007825 u

8. Stability Curve Atomic number Z Neutron number N Stable nuclei Z = N 20406080100 40 100 140 20 60 80 120 Nuclear particles are held together by a nuclear strong force. A stable nucleus remains forever, but as the ratio of N/Z gets larger, the atoms decay. Elements with Z > 82 are all unstable.

9. Types of Radioactivity: There are three major types of radiation that the nuclear physicist is concerned with: alpha, beta, and gamma. –Alpha radiation consists of particles, alpha particles. The alpha particles are actually helium nuclei. –Beta radiation is also made up of particles – electrons. –Gamma radiation is made up of very short wavelength electromagnetic waves. The reason for the odd names is a simple one. –The types of radiation were discovered before the particles were. So Ernest Rutherford discovered alpha particles before anyone knew anything about helium nuclei.

10. The Alpha Particle An alpha particle  is the nucleus of a helium atom consisting of two protons and two neutrons tightly bound. Charge = +2e - = 3.2 x 10 -19 C Mass = 4.001506 u Mass = 4.001506 u Relatively low speeds (  0.1c ) Not very penetrating Not very penetrating

11. The Beta-minus Particle A beta-minus particle    is simply an electron that has been expelled from the nucleus. Charge = e - = -1.6 x 10 -19 C - High speeds (near c) - Mass = 0.00055 u Mass = 0.00055 u - Very penetrating Very penetrating-

12. The Positron A beta positive particle    is essentially an electron with positive charge. The mass and speeds are similar. Charge = +e - = 1.6 x 10 -19 C + High speeds (near c) + Mass = 0.00055 u Mass = 0.00055 u + Very penetrating Very penetrating+

13. The Gamma Photon A gamma ray  has very high electromagnetic radiation carrying energy away from the nucleus. Charge = Zero (0)  Mass = zero (0)  Speed = c (3 x 10 8 m/s)  Most penetrating radiation 

14. Tomorrow: Alpha, Beta (+), Beta (-) and Gamma decay models using elements To do: –Festo Evaluation –Quest Questions