Matter and Radiation

Question 1

What is specific charge?

Answer 1

It is the charge of a particle (C) divided by its mass (kg)

Question 2

Describe the strong nuclear force

Answer 2

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.

Question 3

Why are neutrons needed to keeps the nucleus together?

Answer 3

They space the protons out so the EM repulsion is not so great that it breaks up the nucleus.

Question 4

Why do you need more neutrons than protons in heavy elements to keep the nucleus stable?

Answer 4

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.

Question 5

How does alpha radiation work?

Answer 5

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.

Question 6

Describe beta- decay

Answer 6

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.

Question 7

How does gamma decay occur?

Answer 7

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.

Question 8

What are electromagnetic waves?

Answer 8

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.

Question 9

What is a photon?

Answer 9

A short burst (packet) of electromagnetic waves.

Question 10

How does a PET scanner work?

Answer 10

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.

Question 11

Describe beta+ decay

Answer 11

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.

Question 12

What is rest energy?

Answer 12

A measure of a particle’s energy when it is not moving measured in eV

Question 13

What is the total energy of a particle?

Answer 13

It’s rest energy add its kinetic energy

Question 14

How to convert from joules to eV

Answer 14

Divide the joules by 1.6x10-19

Question 15

What is 1eV?

Answer 15

The energy an electron gains when accelerated by 1V

Question 16

Describe pair production

Answer 16

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.

Question 17

Feynman diagram of repulsion between two protons

Answer 17

Two protons go towards each other. Virtual photon (represented by gamma symbol) shot from one to the other. Both turn outwards.

Question 18

Feynman diagram of neutron neutrino interaction

Answer 18

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.

Question 19

Feynman diagram of proton antineutrino interaction

Answer 19

Both go towards each other. W+ boson shot from proton. Proton becomes neutron and antineutrino becomes beta+ particle. Both turn outwards.

Question 20

Feynman diagram of beta- decay

Answer 20

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.

Question 21

Feynman diagram of beta+ decay

Answer 21

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.

Question 22

Feynman diagram of electron capture

Answer 22

Proton and electron going towards each other. W+ boson shot from the proton. Proton becomes neutron. Electron becomes neutrino. Both turn outwards.

Question 23

Define isotopes

Answer 23

Atoms with the same number of protons and different numbers of neutrons.

Question 24

Describe annihilation

Answer 24

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.