Board Work 1.What is the electrical interaction between a.a proton and another proton in a nucleus? b.a proton and a neutron in a nucleus? c.a neutron and another neutron in a nucleus?

Nuclear Physics Chapters 33–34

Objectives Describe the different types of nuclear reactions and identify the properties of nuclei undergoing them. Identify reactions and products in the nuclear power cycle and nuclear weapons.

Nucleons Source: Griffith, Physics of Everyday Phenomena

Poll Question The electric force tends to A.make nucleons stick together. B.push nucleons apart.

Nuclear Forces Electrostatic force (Coulomb’s Law) –Protons repel protons Strong nuclear force –Nucleons attract at short distances

Identifying Nuclei Number of protons = atomic number Z –determines the element Number of neutrons N –Isotope: same Z, different N N + Z = mass number A Isotope name: Name-A (e.g. Carbon-12)

Board Work 2.Find the elements with these atomic numbers: a.11 b.23 3.Find the atomic numbers of the following elements: a.Chlorine b.Magnesium

Board Work 4.What isotope has 16 protons and 16 neutrons?

Nuclear Reactions Parent  Daughter(s) + “particles”

Decay Timescale 50% chance a nucleus will decay in one half-life Source: Griffith

Poll Question The fraction of parent nuclei remaining after two half-lives is A.None — it has all decayed. B.1/2. C.1/4. D.1/8.

Nuclear Reaction Types Alpha decay Beta decay Gamma emission Fission Fusion

Main Radioactive Emissions Source: Griffith

Alpha Decay Nucleus emits an alpha particle = 2 p + 2 n (helium-4 nucleus) Daughter nucleus has Z – 2, N – 2, A – 4

Poll Question After alpha decay, the atomic number of a nucleus is A.larger B.smaller C.the same as before.

Poll Question After alpha decay, the mass number of a nucleus is A.larger B.smaller C.the same as before.

Beta decay n= neutron p + = proton e – = electron (beta particle) e = electron anti-neutrino e –, e escape, p + remains in nucleus Daughter has same A, Z + 1, N – 1 n  p + + e – + e

Poll Question After beta decay, the atomic number of a nucleus is A.larger B.smaller C.the same as before.

Poll Question After beta decay, the mass number of a nucleus is A.larger B.smaller C.the same as before.

Gamma Emission Excited nucleus emits a high-energy photon (gamma-ray) Occurs only after another decay type Source: Griffith

Poll Question After gamma emission, the atomic number of a nucleus is A.larger B.smaller C.the same as before.

Board Work 5.Find the daughters of the following nuclear decays: a. 239 Pu   + b. 99 Mo   +

Nuclear Stabilities Source: Hodgson et al., Introductory Nuclear Physics

Think Question Which kind of atomic nuclei tend to undergo alpha decay? A.Nuclei with large mass number A. B.Nuclei with too many neutrons. C.Very light (low Z) nuclei. D.Nuclei with too many protons.

Think Question Which kind of atomic nuclei tend to undergo beta decay? A.Nuclei with large atomic number Z. B.Nuclei with too many neutrons. C.Very light (low Z) nuclei. D.Nuclei with too many protons.

Fission Nucleus breaks into two large fragments plus several neutrons Source: Griffith

Fusion Two nuclei combine to make a larger nucleus Neutrons usually released as well Requires extremely high energies (temperature) to overcome nucleus- nucleus electric repulsion

Binding Energy Source: Georgia State U., Hyperphysics fission fusion

Think Question What sort of nuclei release energy by fission? A.Nuclei lighter than iron. B.Nuclei about as heavy as iron. C.Nuclei heavier than iron.

Summary Nuclei contain positive protons and neutral neutrons. Nuclear stability is a balance between electrostatic repulsion and the attractive strong force.

Summary Radioactive atoms can emit alpha particles, beta particles, and gamma rays. Nuclei can also split apart (fission) and combine (fusion). Reaction types depend on nuclear characteristics.

Reading for Next Time Nuclear fission and fusion –characteristics of reacting nuclei –conditions when reactions occur