Physics 4 – April 6, 2018 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 Assignment: p283 #1-13 (Checked Thurs) Agenda: Photons and EM radiation Atomic emission/absorption spectra Nuclides Nuclear and particle symbols Radioactive decay types Radioactivity rates

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 = frequency

Photons and the EM Spectrum EM radiation is delivered as quantized photons with an energy of E = hf = hc/ h = 6.63 x 10-34 J∙ s

Atomic Emission 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. Energy transitions occur between the ground state and excited states. “NEON” LIGHTS!

Absorption Spectra 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.

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 .

Table of the Nuclides http://atom.kaeri.re.kr/nuchart/ Table of the nuclides Cell includes information about mass, energy stability, decay modes and half-life. OR % abundance

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

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.

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

Exit slip and homework Exit Slip – State the three kinds of radiation and identify their mass, charge, particle identifications and relative energy. What’s due? (homework for a homework check next class) p283 #1-13 (Checked on Thursday) What’s next? (What to read to prepare for the next class) Read 7.1