Matter and Radiation Flashcards
What is specific charge?
It is the charge of a particle (C) divided by its mass (kg)
Describe the strong nuclear force
It is the force of that overcomes electrostatic repulsion to keeps the protons and neutrons in a nucleus together. It has as range of about 3-4fm (X10-15). It is an attractive force between this and 0.5fm. Below this it is a repulsive force that prevents neutrons and protons being pushed into each other.
Why are neutrons needed to keeps the nucleus together?
They space the protons out so the EM repulsion is not so great that it breaks up the nucleus.
Why do you need more neutrons than protons in heavy elements to keep the nucleus stable?
Because as the proton number increases, so does the overall EM repulsion so they need even more neutrons to separate them out more so this repulsion isn’t too great.
How does alpha radiation work?
An unstable element emits an alpha particle (2 protons and neutrons) from its nucleus and therefore becomes a different element with an atomic number of two less and a mass number of four less.
Describe beta- decay
In an unstable nucleus a neutron changes into a proton and emits a beta- particle instantly. Also an anti-electron neutrino is emitted to conserve energy. This creates a new element with a proton number of one more and an equal mass number.
How does gamma decay occur?
It happens in elements with too much energy (in excited state) after they have undergone beta or alpha decay so they lose it by emitting gamma radiation.
What are electromagnetic waves?
Transverse waves that go through empty space, oscillating magnetic and electric fields at right angles to each other, have a speed of 3x10^8 m/s.
What is a photon?
A short burst (packet) of electromagnetic waves.
How does a PET scanner work?
A positron emitting isotope is administered to the patient and some of it reaches the brain. Each positron meets an electron and they are annihilated producing two gamma photons which are sensed by detectors linked to computers that build an image of the brain from the signals.
Describe beta+ decay
In an unstable nucleus with too many protons, a proton changes into a neutron and instantly emits a beta+ particle. Also an electron neutrino is emitted. The new element has a proton number of one less.
What is rest energy?
A measure of a particle’s energy when it is not moving measured in eV
What is the total energy of a particle?
It’s rest energy add its kinetic energy
How to convert from joules to eV
Divide the joules by 1.6x10-19
What is 1eV?
The energy an electron gains when accelerated by 1V
Describe pair production
A photon passing near a nucleus or electron can spontaneously produces a particle and its antiparticle, which shoot off in opposite directions, and vanishes if it has more energy than the rest masses combined. The left over energy is the total kinetic energy of both of the particles.
Feynman diagram of repulsion between two protons
Two protons go towards each other. Virtual photon (represented by gamma symbol) shot from one to the other. Both turn outwards.
Feynman diagram of neutron neutrino interaction
Both go towards each other. W- boson shot from neutron. Neutron goes to proton and the neutrino to a beta- particle and both turn outwards.
Feynman diagram of proton antineutrino interaction
Both go towards each other. W+ boson shot from proton. Proton becomes neutron and antineutrino becomes beta+ particle. Both turn outwards.
Feynman diagram of beta- decay
Neutron shoots a W- boson. Neutron becomes a proton. At the end of the W- boson path is a beta- and an antineutrino. All turn outwards.
Feynman diagram of beta+ decay
Proton shoots a W+ boson. Proton becomes a neutron. At the end of the W+ boson path is a beta+ and a neutrino. All turn outwards.
Feynman diagram of electron capture
Proton and electron going towards each other. W+ boson shot from the proton. Proton becomes neutron. Electron becomes neutrino. Both turn outwards.
Define isotopes
Atoms with the same number of protons and different numbers of neutrons.
Describe annihilation
It occurs when a particle and its antiparticle meet and their mass is converted into radiation energy. Two photons are produced leaving in opposite directions to conserve momentum.
