Particles and Radiation Flashcards
What are Kaons
Kaons are much heavier and unstable than Pions
Kaons have a very short life time and decay into Pions
K+, K0,K-
Pions
Pions (π- mesons) are the lightest mesons
π+,π0, π-
Anti particles of π0 is itself
Pions are the exchange particle of the strong nuclear force
Mesons
Type of hadron that interact with baryons via the strong nuclear force
All unstable, baryon number = 0 as they’re not baryons
Its a quark and anti-quark pair
Radioactive decay
Some isotopes are stable but others are not
Those which are unstable release radiation and change into more stable isotopes, (normally a different element)
strong nuclear force
Responsible for keeping the protons and neutrons together in the nucleus
attractive force stonger than the elctromagnetic force
repulsive for very small seperationsof nuceons, less than about 0.5fm
past 0.5fm it becomes attractive and rapidly fall to 0 past 3fm
EMRF extends over a much larger range
Proton charge and mass
Charge = + 1.60x10^-19
Mass = 1.67x10^-27
Neutron charge and mass
Charge = 0
Mass = 1.67x10^-27
Electron charge and mass
Charge = -1.60x10^-19
Mass = 9.11x10^-31
Specific charge
Specific charge = charge/mass
Charge = coulombs (C)
Mass = kg
Specific charge = C/kg^-1 ( coulombs per kilogram
Isotopes
Atoms with the same number of protons and electrons but different number of neutrons
Forces in the nucleus
The electromagnetic force causes the positively charged protons in the nucleus to repel each other
The gravitational force causes all the nucleons in the nucleus to attract each other due to their mass
Alpha decay
Only happens in very big atoms? More than 82 protons)
The nuclei of these atoms are just too big for the strong nuclear force to keep them stable
To make themselves more stable these emit an alpha particle from their nucleus.
When emitted the proton number decreases by 2 and the neutron number by 4
Counting alpha particles
Alpha particles have a very short range( a few cm in air) this can be observed by seeing the track left by alpha particles in a cloud chamber
You could also use a greiger counter or a spark counter
These devices measure the amount of isonisng radiation
Beta-minus decay
Involves a neutron changing into a proton
Beta decay is the emission of an electron from the nucleus along with an antineutrino particle. Beta decay happens in isotopes that are “neutron rich”.
When a nucleus ejects a beta particle one of the neutrons in the nucleus is changed into a proton. PN increases by 1and the nucleon number stays the same. The antineutrino released carries away some energy and momentum
Happens via the weak in the interaction
Electromagnetic spectrum
Longest wavelength and shortest frequency
Radio waves
Microwaves
Infrared radiation
Visible light
Ultraviolet
X-rays
Gamma rays
Shortest wavelength and longest frequency
Pair production
When energy is converted into mass and mass can turn into energy
Can only happen if there is enough enery to produce masses of the particles
The particles produced curve away from each other in opposite directions as thyre in an applied magnetic field and have opposite charges
pair production proton example
fire two protons with a large amount of kinetic energy at each other, (moving at high speed), ending up with a lot of energy at the point of impact. This energy can be converted into more particles. If an extra proton is formed then so is an antiproton along with it
pair production electron
if a photon has enough energy then it can produce an electron-positron. Tends to happen when a photon passes near a nucleus
Antiparticle for:
1. Proton
2. Neutron
3. Electron
4. Neutrino
- Antiproton
- Antineutron
- Positron
- Antineutrino
Rest energy for proton/ antiproton
938(.3)MeV
Rest energy for neutron/ antineutron
939(.6)MeV
Rest energy for electron/ positron
0.51(1)MeV
Rest energy for neutrino/ antineutrino
0MeV
Hadrons
Since protons are positively charged they need a strong force to hold them together- the strong nuclear force or the strong interaction
Not all particles can feel the SNF, the ones that can are called hadrons
They aren’t fundamental particles
They’re made up of smaller particles called quarks
Two types of hadrons- mesons and baryons
Baryons
Protons and neutrons are both baryons
All baryons are unstable except a free proton
Means all baryons apart from protons decay to become other particles
The particle a baryon decays in depends on what it started as but all baryons except a proton eventually decay into a proton
Antibaryons
Antiparticles of protons and neutrons, antiprotons and antineutrons
But antiparticles are annihilated when they meet they’re corresponding particle so that means you can’t find them in ordinary matter
Baryon number
Baryon number is a quantum number that must be conserved
Baryon number of baryons = +1
Baryon number of antibaryons =-1
Other particles = 0
Neutron decay
When a neutron decays it forms a proton, electron and an antineutrino
n -> p + e- + /ve
Detection of mesons
High-energy particles from space called cosmic rays are constantly hitting the earth
Cosmic rays interact with molecules in the atmosphere produce ‘showers’ of lots of high-energy particles, including pions and kaons.
Known as cosmic ray showers which can be observed the tracks of these particles with a cloud chamber
Leptons
Fundamental particles that don’t feel the strong nuclear force
Only really interact with other particles via the weak interaction
Leptons - electron and muons
Electrons are stable leptons
Muons are just like heavy electrons but they’re unstable and eventually decay into ordinary electrons
Leptons electrons/ muons and neutrinos
Electrons and muons each come with with their own neutrino, the electron neutrino and the muon neutrino
Neutrinos have zero mass and zero electric charge so they don’t do much and only take part in the weak interaction and can in fact pass through the earth without anything happening to it
Antiparticles for leptons
Electron - positron
Muon - antimuon
Electro neutrino - electron antineutrino
Muon neutrino - muon antineutrino
Lepton number
Lepton number is a quantum number
Each lepton is given a lepton number of +1
Strange particles
Strange particles have a property called strangeness
Strange particles interact via the strong interaction, in which strangeness is conserved
Conservation of strangeness means that strangeness particles can only be created in pairs
Stangeness is a quantum number
All leptons have a strangeness of 0
Strange particles decay through the weak interaction but not conserved in the weak interaction
Up quark
Symbol = u
Charge = +2/3
Baryon number = +1/3
Strangeness = 0
Down quark
Symbol = d
Charge = -1/3
Baryon number = +1/3
Strangeness = 0
Strange quark
Symbol = s
Charge = -1/3
Baryon number = +1/3
Strangeness = -1
Anti- strange quark
Symbol = /s
Charge = +1/3
Baryon number = -1/3
Strangeness = +1
Anti-up quark
Symbol = ū
Charge = -2/3
Baryon number = -1/3
Strangeness = 0
Anti-down quark
Symbol = /d
Charge = +1/3
Baryon number = -1/3
Strangeness = 0
Quark composition of baryons
All baryons are made up of 3 quarks
Antibaryons are made up of 3 antiquarks
Quark composition of mesons
1. K+
2. Ko
3. K-
4. /ko
5. π+
6. πo
7. π-
All mesons are made up of a quark and antiquark pair
1. u/s
2. d/s
3. sū
4. s/d
5. u/d
6. uū or d/d or s/s
7. dū
Quark confinement
Not possible to get a quark by itself
If you blasted a proton with a lot of energy, a single quark would not be removed
The energy you supplied would just get changed into matter
1- a proton (uud)
2- energy supplied to remove u quark
3- when enough enrgy is supplied a uū pair produced and u quark stays in proton ( uū and uud)
Weak interaction
Beta-minus decay
In B- decay a neutron is changed into a proton - in other words udd changes into uud. Means a d quark changes into a u quark
Only the weak interaction can do this
A quark changing into another quark is called changing a quarks character
Electron and electron antineutrino emitted
Weak interaction
Beta-plus decay
Some unstable isotopes like carbon-11 decay by beta-plus emission
B+ decay means a positron is emitted
In this case it means a proton changes into a neutron, so a u quark changes to a d quark and a positron and electron neutrino is emitted
Particle exchange
All forces are caused by particle exchange
So when two particle interact and exert a force on one another, something must happen to let one particle known that the other ones there
Repulsion
Skating example
Exchange particles
Imagine two skaters facing each other throwing a ball
Each time the ball is thrown or caught they get pushed apart
Happens as the ball carries momentum ( mass x velocity )
People represent particles that are interacting with each other, and the ball is an ‘ exchange particle ‘ that causes a repulsive force
Particle exchange
Attraction
Skating example
Skaters facing away from each other and throw a boomerang between them. Each time the boomerang is thrown or caught the people cleft pushed together
The people represents particles that interact with each other and the boomerang is an ‘exchange particles’
- Strong interaction
- Electromagnetic interaction
- Weak interaction
- Gauge boson - Pions (π+-o)
Particles effected - hadrons only - Gauge boson - virtual photon
Particles affected - charged particles only
3 - gauge boson - W+, W- bosons
Particles affected - all types of
Four fundamental forces
Strong force
Weak force
Electromagnetic force
Gravitational force
Beta minus decay equation
n — p + e- + /ve
W-on transfers a negative charge across the other side so the charges stay balance
Beta plus decay
p — n + e+ + Ve
W+
Electron capture
P + e — n + Ve
W+ boson
—>
Electron proton collisions
P+e- —> n + Ve
W-
<—
Annihilation
When a particle meets us antiparticle the result is annihilation
All the mass of the particle and the antiparticle gets converted back into energy in the form of two gum photons
Electromagnetic repulsion
e + e —> e + e
Virtual photon
Gauge boson
A virtual particle which allows forces to act in a particle interaction
They are also known as exchange particles
