3.2.1.3 - Particles, Antiparticles and Photons Flashcards
What is a photon?
Packet of electromagnetic waves.
The greater the frequency of the radiation…
…the greater the energy of the photon.
In E=hf what does h and f mean?
h= Planck’s constant and f= frequency.
In E=hf what does f have to be in?
m
How do you convert nm into m?
Times by 10^-9
In E=hc/λ what does c mean?
c= speed of light
What is one electron volt?
The energy change of an electron when it moves through a potential difference of 1 volt.
Energy in eV =
Energy of photon / 1.6x10^-19
What happens when energy is converted into mass?
iYou get equal amounts of matter and antimatter.
By what are electromagnetic waves emitted?
By a charged particles when it loses energy.
When are electromagnetic waves emitted?
A fast moving electron is stopped or slows down or changes direction.
An electron in a shell of an atom moves to a different shell of lower energy.
What is the antiparticle of a proton?
Antiproton.
What is the antiparticle of a neutron?
Antineutron.
What is the antiparticle of an electron?
Positron.
What is the antiparticle of a neutrino?
Antineutrino.
What are the similarities between an antiparticle and corresponding particle?
Antiparticles have the same rest mass as the particle but have the opposite charge.
1MeV =
1.6x10^-13J
When does annihilation occur?
When a particle and a corresponding antiparticle meet and their mass is converted into energy.
Why are two photons produced during annihilation?
Two are produced with equal energies because of conservation of energy.
What happens when an electron and positron annihilate?
Their mass is converted into energy and a pair of gamma rays are produced to conserve momentum.
Minimum energy of each photon produced in annihilation?
E0
What happens in pair production?
A photon creates a corresponding particle and antiparticle, and vanishes in the process.
When does pair production occur?
It only happens when one photon has enough energy to produce a mass - only gamma ray photons have enough energy.
Why does pair production tend to happen near a nucleus?
It helps conserve momentum.
What and why is usually produced in pair production?
Electron-positron pairs because they have a relatively low mass.
What is the minimum energy for a photon to undergo pair production equal to?
The total rest energy of the particles produced.
Why are the particle tracks curved during pair production?
There’s usually a magnetic field present in the experiment. They curve in different direction because of the opposite charges of the electron and positron.
Minimum energy of each photon produced in pair production?
2E0
What changes occur in a proton rich nucleus when it emits a positron?
Proton turns into a neutron. Positron and a neutrino are created and emitted from the nucleus.
Differences between pair production of a positron and an electron from positron emission?
- no photons involved in positron emission.
- no neutrinos are emitted in pair production.
