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Notes on Nuclear Physics Radioactivity As the name implies, nuclear physics is
all about studying the cores of atoms.
As a refresher, an atom is made of 3 basic particles. Protons and neutrons sit at the nucleus. Electrons lie in shells farther out.
notes
Notes on Nuclear Physics Radioactivity As the name implies, nuclear physics is
all about studying the cores of atoms.
As a refresher, an atom is made of 3 basic particles. Protons and neutrons sit at the nucleus. Electrons lie in shells farther out.
The core of any atom with more protonsthan lead is unstable. When it undergoes a change, it releases dangerous energy. We call this process “radioactivity”.
Notes on Nuclear Physics Types of Radiation
Alpha
All unstable atoms emit radiation. There are 3 basic types of radiation:
α: These are just helium nuclei. They have the most energy, but are stopped by clothing or a piece of paper.
Notes on Nuclear Physics Types of Radiation
Alpha
Beta
All unstable atoms emit radiation. There are 3 basic types of radiation:
α: These are just helium nuclei. They have the most energy, but are stopped by clothing or a piece of paper.
β: These are electrons. They can be stopped by thin sheet metal or aluminum.
Notes on Nuclear Physics Types of Radiation
Alpha
Beta
Gamma
All unstable atoms emit radiation. There are 3 basic types of radiation:
α: These are just helium nuclei. They have the most energy, but are stopped by clothing or a piece of paper.
β: These are electrons. They can be stopped by thin sheet metal or aluminum.
γ: This is high energy light. They have the least energy of the 3, but can penetrate through several inches of solid lead.
Notes on Nuclear Physics Nuclear Fission
So how and why do atoms emit radiation?
The nucleus of an atom wants to be stable and in balance. All atoms heavier than lead don’t have this balance.
To get balanced, the nucleus spits out radiation, changing element as it goes, until it reaches a point where things are stable.
An example “decay tree” is shown at right.
Notes on Nuclear Physics Nuclear Fission
We can measure how long it should take for each element to decay to another, depending on how unstable the nucleus is.
Example: it takes over 700 years for Thorium to decay to Radon, but only 15 days for Radon to decay to Actinium!
Each element has its own decay time.
Notes on Nuclear Physics Half-Life We have a term to measure how long it
takes elements to decay. We call it “half-life”.
The half life of an element is the time it takes for half of a sample to decay to another element.
Notes on Nuclear Physics Half-Life We have a term to measure how long it
takes elements to decay. We call it “half-life”.
The half life of an element is the time it takes for half of a sample to decay to another element.
T = # of half lives
Notes on Nuclear Physics Half-Life Carbon has a slightly radioactive isotope
known as “carbon 14”. It has a half-life of 5370 years. We can tell pretty easily in most fossils how much C-14 something started with and how much it still has.
Using this, we can determine the age of fossils relatively accurately in a process we call “radiocarbon dating”.
Notes on Nuclear Physics Half-Life Carbon has a slightly radioactive isotope
known as “carbon 14”. It has a half-life of 5370 years. We can tell pretty easily in most fossils how much C-14 something started with and how much it still has.
Using this, we can determine the age of fossils relatively accurately in a process we call “radiocarbon dating”.
Example: If half of the C-14 is missing, the fossil is 5370 years old. If ¾ are missing, it must be 10,740 years old.
Notes on Nuclear Physics Mass-Energy Equivalence
In a nuclear power plant, we force enriched uranium to undergo decay.
Notes on Nuclear Physics Mass-Energy Equivalence
In a nuclear power plant, we force enriched uranium to undergo decay.
If we shoot a neutron at the Uranium, it tips the balance, forcing it to split almost immediately into Krypton and Barium. This releases tons of energy in the form of radiation. More importantly though, it also releases more neutrons…
Notes on Nuclear Physics Mass-Energy Equivalence
Where does this energy come from?
From Physics 1 you learned that work = force • distance. If you try to pull a proton or neutron from a nucleus it will take a LOT of force. This means there’s a lot of energy holding the nucleus together. More than one would think.
Notes on Nuclear Physics Mass-Energy Equivalence
Where does this energy come from?
From Physics 1 you learned that work = force • distance. If you try to pull a proton or neutron from a nucleus it will take a LOT of force. This means there’s a lot of energy holding the nucleus together. More than one would think.
This energy is storedup as the particles thatmake up the nucleus.
You’ve actually seenthe equation for this!
Notes on Nuclear Physics Mass-Energy Equivalence
Einstein came up with the equation to find out how mass stores energy.
E = m • c2
This equation says that mass and energy are basically the same thing. Think of mass as solidified energy. In nuclear physics, we can translate mass to energy and back again!
Notes on Nuclear Physics Nuclear Weapons
Atomic bombs worked on the principle of releasing all this energy at once.
If you have some plutonium and shoot a neutron at it, it will fission. It shoots out more neutrons. This will fission more plutonium. This process will keep going as long as it can in a chain reaction.
If you have enough – a critical mass – it will explode in an amazingly violent blast.
So all you need for a nuclear bomb is to get a critical mass of plutonium together.
Notes on Nuclear Physics Nuclear Weapons
So all you need for a nuclear bomb is to get a critical mass of plutonium together.
Little Boy Fat Man
Vocabulary Nuclear Physics
Radioactivity
Fission
Half-Life
Radiocarbon dating
The study of processes that occur between atomic nuclei and within atoms.
Any process in which the nucleus of an atom releases energy.
The splitting of a nucleus into 2 other elements.
The time it takes for half of a sample to decay to another element.
The process of determining the age of a fossil by the remaining amounts of C-14.
vocab
Vocabulary Chain Reaction
Critical mass
A process that accelerates and grows without external influence.
The amount of radioactive material needed to reach a sustained explosion.
vocab
Equations Half-Life
equations
Nt = N0(1/2)
Nt: Amount of radioactive material left after a specified time.
N0: Initial amount of radioactive material.
(the above 2 need to be in the same units)
t: Elapsed time
t½: Half-life of the material
(the above 2 need to be in the same units)
This equation will tell us how much of a radioactive material remains after a certain amount of time.
E
V
S
t_ t½
Equations Energy-Mass Equivalence
equations
E = m•c2
E: Energy. In Joules.
m: Mass in kilograms.
c: The speed of light. 3x108 m/s.
This equation can be used to translate energy to mass and back again.
E
V
S
Exit Question
How many joules of energy are stored in 4 grams of matter?
