Physics 4 – April 20, 2017 P3 Challenge – Sketch the nuclear model of the atom from what you remember from chemistry. Indicate the charge, relative mass and location of protons, neutrons and electrons.

Objectives/Agenda/Assignment 7.1 Radioactivity 7.2 Nuclear reactions Assignment: p283 #1-13 p294 #16-24 Agenda: Photons and EM radiation Atomic emission/absorption spectra Nuclides Nuclear and particle symbols Radioactive decay types Radioactivity rates Binding energy and nuclear stability Nuclear reactions (fission/fusion)

Electromagnetic Radiation Electromagnetic radiation consists of mutually perpendicular alternating magnetic and electric fields traveling in phase with a specific frequency and wavelength. All electromagnetic radiation travels at the same velocity: the speed of light (c), 3.00  108 m/s. Therefore, c = f  = wavelength f = frequencey EM radiation is delivered as quantized photons with an energy of E = hf = hc/

Atomic Spectra If you pass an electrical current through a sample of atomic gas, it will emit a line spectra reflecting the energy transitions present in the atomic structure. If you pass white light through a gas sample, some wavelengths of light (the ones that match the energy transitions for the atomic structure) will be absorbed and create dark lines. The bright lines of an emission spectrum from an atom and the dark lines of an absorption will be located at the same wavelengths/frequencies. Energy transitions occur between the ground state and excited states.

Nuclides Every atom that exists is a type of nuclide that contains a specific number of protons and neutrons. (and electrons to make a neutral atom) The number of protons identifies the element and is the atomic number Z. The sum of the protons and neutrons is the mass number, A. The element name followed by the mass number identifies a nuclide. Ex: Iron-56 Symbolically represented with 26 56 Fe . http://atom.kaeri.re.kr/nuchart/ Table of the nuclides Cell includes information about stability, decay modes and half-life.

Nuclear symbols Besides the nuclide symbols there are other symbols that are used within nuclear reactions. These symbols use the pattern of a top number equal to mass number and the bottom number equal to charge.

Types of radioactive decay There are three types of nuclear decay modes: Alpha decay  a helium nucleus Beta decay  an electron Positron emission + a positron Another kind of radiation is often emitted along with these decay modes: Gamma radiation  high energy EM radiation

Examples of types of decay Alpha decay: Ex: Po-212 Beta decay: Ex: Th – 234 Gamma decay: Ex: U-238 Decay series: Once a stable nucleus decays, it will initial a series of decays until a new stable nucleus is obtained.

Properties of Radiation and Safety

Radioactive decay Same kind of decay as the decay rate of a capacitor. Radioactive decays are random spontaneous events that happen at a rate that is proportional to the amount of material present. N/ t = kN k is the rate constant and the number of nuclei decreases exponentially. In one k, 37% of the sample has decayed. N = No e-t/k Half-life = t1/2 = k (ln2) t1/2 listed for nuclides

Binding Energy and nuclear stability The energy released in a decay come from the energy required to bind a nucleus together. It is the energy of the mass defect that occurs when a nucleus forms. A nucleus has a mass that is less than the sum of its parts by  = the mass defect The binding energy is given by E = c2 . (the famous equation) Graph of Binding Energy / Mass number Ni-62 is most stable

Nuclear reactions Fission: When a large atom is reacted with a neutron, it may form a nuclide that splits into two daughter nuclei. Ex: Fusion: When two small atoms collide to form a larger nuclide. Nuclides larger than Ni-62 may do fission. Smaller may do fusion. The energy of nuclear reactions is also related to it’s mass changes.

Exit slip and homework Exit Slip – Nitrogen-14 has a mass of 14.003074 u. What is the binding energy of a Nitrogen-14 nucleus in J? (Atomic number= 7) What’s due? (homework for a homework check next class) p283 #1-13 and p294 #16-24 (I will post solutions on Sunday) What’s next? (What to read to prepare for the next class) Read 7.1, 7.2 and 7.3