1. 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.

2. 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)

3. 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/

4. 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.

5. 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 Fe .
Table of the nuclides
Cell includes information about stability, decay modes and half-life.

6. 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.

7. 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

8. 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.

9. Properties of Radiation and Safety

10. 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

11. 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

12. 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.

13. Exit slip and homework
Exit Slip – Nitrogen-14 has a mass of 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