Nuclear Physics

1. (not to scale) Nuclear Physics At this point we have established that the atom has three main components, positively charged protons (p+), neutral neutrons (no) and negatively charged electrons (e-) . The protons and neutrons make up the vast majority of the atom's mass, and are located together at the center of the atom, called the nucleus. Most of the atom is empty space, and electrons are located at a distance from the nucleus, in discrete energy levels.

2. Nuclear Physics: Terminology • Atomic Number (charge number) - the number of protons in an atom/nucleus. • This number defines the particular element. • Mass Number - the number of nucleons in an atom (# of p+ plus # of no) • Atomic Mass Unit (AMU) = Defined as 1/12 of the mass of a carbon 12 atom. • 1 AMU is roughly equal to mass of a p+ or no. • Isotopes - atoms of the same element with different numbers of neutrons • Nucleons  - the two constituent particles of a nucleus (protons and neutrons).

3. Mass Number: Number of protons plus neutrons Element Symbol Atomic Number = number of protons (or # of positive charges) Electron Neutron Proton Nuclear Physics: Notation This notation can also be used for single particles…

4. Nuclear Reactions During nuclear reactions, both mass and charge numbers must be conserved. Instead of an equation with an equal sign, a reaction is shown with an arrow. Example (not a actual reaction)

5. - p+ no no Alpha Particle (a) Two protons and two neutrons (helium nucleus) p+ Beta Particle (b) A high energy electron Gamma (g) Particle (Ray) A high energy photon Nuclear Physics: Radioactive Decay There are three different types of “particles” that can be given off during radioactive decay. They are:

6. Nuclear Physics: Radioactive Decay a particle: most massive, least “penetrative” b particle: “non-superlative” mass and penetration g particle: least massive (massless) , most “penetrative”

7. Nuclear Physics: Alpha Decay Example: A uranium nucleus spontaneously decays, producing a thorium nucleus and an alpha particle.

8. Nuclear Physics: Beta Decay Example: A thorium nucleus spontaneously decays, producing a protactinium nucleus and an beta particle.

10. Nuclear Physics The atomic mass unit (amu or simply “u”) is defined as 1/12 of the mass of a carbon 12 atom. The atomic mass of pure carbon 12 would be 12 u. This is equivalent to 12 g/mole. So in kilograms, the mass of a carbon 12 atom would be… If 12 u = 1.99 x 10-26 kg 1 u = 1.66 x 10-27 kg

11. Nuclear Physics 1 u = 1.66 x 10-27 kg Using Einstein’s famous E = mc2 equation… The energy equivalent of 1 u is… (1.66 x 10-27 kg)(3 x 108)2 = 1.49 x 10-10 Joules In electron volts, this is equal to… 1.49 x 10-10 Joules x (1 ev / 1.60 x 10-19 J) = 931 Mev 1 u = 931.5 MeV

12. Nuclear Physics The key concept behind the release of energy in fusion (and fission) reactions is binding energy . Binding energy is the energy that is lost when a nucleus is created from protons and neutrons. If you added up the total mass of the nucleons (protons and neutrons) that compose an atom, you would notice that this sum is greater than the actual mass of the atom. This missing mass, called the mass defect, is a measure of the atom's binding energy. It is released during the formation of a nucleus from the composing nucleons. This energy would have to be put back into the nucleus in order to decompose it into its individual nucleons. The greater the binding energy per nucleon in the atom, the greater the atom's stability.

13. Nuclear Physics To calculate the binding energy of a nucleus, all you have to do is sum the mass of the individual nucleons, and then subtract the mass of the atom itself. The mass leftover is then converted into its energy equivalent. The relation between mass and energy is shown in Einstein's famous equation E = mc2. The mass of a proton is 1.007276 u The mass of a neutron is 1.008665 u.

14. The greater the binding energy per nucleonof an atom, the greater it's stability. This is a graph of the relative binding energy per nucleon vs. mass number. Notice that the nuclei of the light elements are generally less stable than the heavier nuclei up to those with a mass number around 56. The nuclei of the heaviest elements are less stable than the nuclei that have a mass number of around 56. From this, you can see that the nuclei around iron are the most stable. This information implies two methods towards the converting of mass into useful amounts of energy: fusion and fission. Average Binding Energy per Nucleon (MeV) Number of Nucleons in Nucleus

19. Nuclear Fission

20. Nuclear Fission

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23. Nuclear Fusion

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25. Nuclear Fusion