Particles

Question 1

Charge plus mass of particles

Answer 1

Proton - charge = +1.6x10^-19. Mass-1.67x10^-27
Neuton has no charge and same mass as proton
Electron=-1.6x10^-19 charge and mass-9.11x10^-31

Question 2

Specific charge

Answer 2

The specific charge of a particle is the charge-mass ratio, and is calculated by dividing a particle’s charge by its mass.

Question 3

Placeholder element

Answer 3

The specific charge of a particle is the charge-mass ratio, and is calculated by dividing a particle’s charge by its mass.

Question 4

Strong nuclear force

Answer 4

The strong nuclear force (SNF) keeps nuclei stable by counteracting the electrostatic force of repulsion between protons in the nucleus (as they have the same charge). It only acts on nucleons and has a very short range, where it is attractive up to separations of 3 fm, but repulsive below separations of 0.5 fm,

Question 5

Unstable nuclei

Answer 5

Unstable nuclei are those which have too many of either protons, neutrons or both causing the SNF to not be enough to keep them stable, therefore these nuclei will decay in order to become stable. The type of decay the nuclei will experience depends on the amount of each nucleon in them.

Question 6

Alpha decay

Answer 6

Alpha decay occurs in large nuclei, with too many of both protons and neutrons.
The proton number decreases by 2.
The nucleon number decreases by 4

Question 7

Beta minus decay

Answer 7

Beta-minus decay occurs in nuclei which are neutron-rich (have too many neutrons).
The proton number increases by 1.
• The nucleon number stays the same.

Question 8

History of beta minus decay

Answer 8

At first, scientists believed that only an electron (beta-minus particle) was emitted from the nucleus during beta-minus decay, however observations of the energy levels of the particles before and after the decay showed that energy was not conserved. This does not follow the principle of conservation of energy, and therefore neutrinos were hypothesised to account for this, and later they were observed.

Question 9

Antiparticles

Answer 9

For every type of particle there is an antiparticle which has the same rest energy and mass but all its other properties are opposite the particles.

Question 10

Photons

Answer 10

Electromagnetic radiation travels in packets called photons, which transfer energy and have no mass.

Question 11

Annihilation

Answer 11

Annihilation is where a particle and its corresponding antiparticle collide, as a result their masses are converted into energy. This energy, along with the kinetic energy of the two particles is released in the form of 2 photons moving in opposite directions in order to conserve momentum.

Question 12

Application of annihilation

Answer 12

PET scanner, which allows 3D images of the inside of the body to be taken, therefore making medical diagnoses easier.
This is done by introducing a positron-emitting radioisotope into the patient, as positrons are released they annihilate with electrons already in the patients system, emitting gamma photons which can easily be detected.

Question 13

Pair production

Answer 13

Pair production is where a photon is converted into an equal amount of matter and antimatter. This can only occur when the photon has an energy greater than the total rest energy of both particles, any excess energy is converted into kinetic energy of the particles.

Question 14

The four fundamental forces

Answer 14

There are four fundamental forces: gravity, electromagnetic, weak nuclear and strong nuclear.

Question 15

Exchange particles

Answer 15

Exchange particles carry energy and momentum between the particles experiencing the force and each fundamental force has its own exchange particles.

Question 16

Interaction , exchange ,range and act on

Answer 16

Interaction
Exchange particle
Range
Acts on

Strong
Gluon
3 × 10-15
Hadrons

Weak
W boson (W +or W-)
10-18
All particles

Electromagnetic
Virtual photon (Y )
Infinite
Charged particles

Gravity
Graviton (not on specification)
Infinite
Particles with mass

Question 17

Clarification of particles

Answer 17

All particles are either hadrons or leptons. Their differentiating property is that leptons are fundamental particles, meaning they cannot be broken down any further, and they do not experience the strong nuclear force. On the other hand, hadrons are formed of quarks (quarks are fundamental particles), and hadrons experience the strong nuclear force.
Hadrons can be further separated into baryons, antibaryons and mesons. Baryons are formed of 3 quarks, antibaryons are formed of 3 antiquarks while mesons are formed from a quark and antiquark.

Question 18

Baryon number

Answer 18

The baryon number of a particle, shows whether it is a baryon (if 1), antibaryon (if -1) or not a baryon (if 0). Baryon number is always conserved in particle interactions.

Question 19

The only stable baryon

Answer 19

The proton is the only stable baryon, therefore all baryons will eventually decay into a proton either directly or indirectly.

Question 20

Lepton number

Answer 20

The lepton number of a particle, shows whether it is a lepton (if 1), antilepton (if -1) or not a lepton (if 0). There are two types of lepton number you need to know, electron lepton number and muon lepton number, which represent the named particle. Lepton number is always conserved in particle interactions.

Question 21

Muon

Answer 21

A muon is sometimes known as a “heavy electron”, and muons decay into electrons.

Question 22

Strange particle

Answer 22

Strange particles are particles which are produced by the strong nuclear interaction but decay by the weak interaction. The only strange particles you are expected to know about are kaons, which decay into pions, through the weak interaction.

Question 23

Strangeness

Answer 23

Strangeness is a property of particles, which shows that strange particles must be created in pairs, as strangeness must be conserved in strong interactions. However, in weak interactions strangeness can change by 0, +1 or -1.

Question 24

How to investigate particle physics

Answer 24

In order to investigate particle physics, particle accelerators may be built however as these are very expensive to build and run, and also produce huge amounts of data, scientific investigations rely on collaboration of scientists internationally.

Question 25

Quarks and antiquarks

Answer 25

Type of quark Charge. Baryon number. Strangeness

Up. +2/3e. +1/3. 0
Down. -1/3e. +1/3. 0
Strange. - -1/3e. +1/3. -1

Question 26

Quark combinations

Answer 26

Particle. Quark combination. Charge strangeness

π0. uū or dd 0. 0
π+. ud. 1. 0
π- ūd. -1. 0
K0. dš or ds. 0. +_1
K+. uš. +1. +1
K- ūs. -1. -1

Question 27

Conservation laws

Answer 27

These properties must always be conserved in particle interactions:
• Energy and momentum
Charge
Baryon number
• Electron lepton number
• Muon lepton number
Strangeness must only be conserved during strong interactions