Physics: Intro to Nuclear Physics Notes 

• The four forces in the universe:  gravity, strong force, weak force, electromagnetism
• Gravity is attraction between objects
• Gravity is only significant for very large objects

Electromagnetism Creates magnetism

• Holds chemical bonds together
• Creates electricity
• Strong & weak Forces act in the nucleus of the atom

The Strong Force

• The glue that binds the nucleus together
• When you release the energy in the nucleus, you get a nuclear bomb and nuclear energy

Fission

• Very large unstable nuclei  can fall apart or can be split
• Purpose is to create large amounts of energy

Nuclear Chain Reaction

1. Neutron is added making the atom unstable

2. Atom falls apart

3. Loss of mass and release of energy

• Utilized in WW2 and nuclear power plants

Fusion

• Occurs under high pressure and temperature
• Small nuclei combine to form large nuclei
• Cannot be controlled
• The Sun turns hydrogen into helium
• Heavier elements are made in supernovas and in star collisions
• Huge amounts of energy are released by fusion
• Used in hydrogen bomb (not WW 2 Bomb) and stars
• Albert Einstein determined that a small amount of mass contains a large amount of energy
• Equation: E+mc^2

• The amount of mass lost when the WW2 Bombs dropped on Japan: 0.7 grams
• The amount of mass the Sun converts to energy each second:  5 million tons
• The amount of years till the Sun runs out of fuel (hydrogen): 5 billion years

The Weak Force

• Takes place in the nucleus
• The weak force is Radioactive BETA decay
• A neutron turns into a proton and an electron

Beta decay is responsible for

• Irritating hydrogen in fusion stars 
• Plate tectonics
• Carbon 14 dating of organic objects 

Carbon Dating

• Cosmic rays cause all living things to be radioactive
• Used to date items up to 60,000 years old
• Amount of atomic bombs tested on Earth: 2,000

Wave Particle Duality

• Light can behave like a wave or a particle
• Light is a transverse wave
• Light does not need a medium
• Light also travels in particles called photons
• Young’s Double Slit Experiment showed that light can behave as both a particle and a wave
•  Two waves combine  form an interference wave

Spectroscopy

• Elements can be identified by their atomic spectrum
• Each type of light corresponds to a specific energy
• Visible light spectrum in order from least to greatest energy “ROY-G-BIV” Highest energy is violet, lowest energy is red
• Higher orbits have higher energy

• When jumping from a low level to a higher level you add energy
• When falling from a higher level to a lower level you remove energy

• Photons are emitted from the atom when an electron falls in energy
• The color of the photon emitted is related to the amount of energy released  
• Spectroscopy: dispersion of light into its available spectrum

• the two types of spectra: continuous, discrete
• In a continuous spectrum, light is composed of a wide unbroken range of colors 
• Materials that create a continuous spectrum: stars and galaxies
• A discrete spectrum only has lines at very distinct colors
• Every element and chemical has a different emission spectrum

The Photoelectric Effect

• Einstein won the Nobel Prize in 1921for the photoelectric effect
• The photoelectric effect: the emission of electrons when electromagnetic radiation (light) falls on an object

• Three things that happen during the photoelectric effect:
• A light photon hits an object
• Energy transfers from the photon to the object
• If the energy is great enough an electron will be ejected by the object

• The threshold frequency is the minimum energy required to eject an electron 
• If energy is below the threshold frequency,  no emission 
• If energy is equal to or greater than the threshold frequency,  electron emitted 
• Only the frequency determines the energy
• The amount of light (intensity) does not matter
• Different substances have  different thresholds 
• Different light has different energy