1. Nuclear Science What is in a nucleus? Why do nuclei decay? Where does radiation come from?

2. Inside Atoms An atom is ~10 nm in diameter (1x10 -10 m) The electrons are the particles in the atom that “fill” most of this space At the center of the atom is a nucleus, which is typically about 5 femtometers across (5x10 -15 m)

3. Inside Nuclei Neutrons and protons form the nucleus of the atom Neutrons and protons form the nucleus of the atom Neutrons and protons have masses that are 5000 times that of the electron, so their mass makes up most of the mass of an atom Neutrons and protons have masses that are 5000 times that of the electron, so their mass makes up most of the mass of an atom

4. More about nuclei Neutrons and protons are called nucleons Neutrons and protons are called nucleons Protons have a positive charge (same size, but opposite sign as electron) Protons have a positive charge (same size, but opposite sign as electron) Neutrons are have no net charge Neutrons are have no net charge

5. More about atoms Chemical properties of atoms are determined by the number of electrons and protons in a neutral atom, so the number of protons in the nucleus determines chemical properties of an element. The number of neutrons does not affect most of the chemical properties of an element. Example: The element Carbon has 6 electrons and 6 protons

6. Elements and isotopes Different nuclei (isotopes) of the same element can have different numbers of neutrons. Carbon-11 Z=6 (protons) N=5 (neutrons) Carbon-12 Z=6 (protons) N=6 (neutrons) Carbon-13 Z=6 (protons) N=7 (neutrons) Carbon-14 Z=6 (protons) N=8 (neutrons)

7. Chart of Elements OR Chart of Nuclides Element - Carbon Carbon isotopes Z N

8. Z N What does the chart tell us? Z N There are LOTS of nuclides There are LOTS of nuclides There are many isotopes of most elements There are many isotopes of most elements Blue nuclides are “stable” Blue nuclides are “stable” Nuclides with N≥Z are more stable than nuclides Nuclides with N≥Z are more stable than nuclides

9. What happens to “unstable” nuclei

10. Is that all? Nuclei can also emit nucleons (neutrons and protons) Nuclei can also emit nucleons (neutrons and protons) Nuclei can break into chunks (fission) Nuclei can break into chunks (fission)