1.7 Particles and nuclear structure

Question 1

What is an antiparticle?

Answer 1

An antiparticle has the same properties as its equivalent particle (e.g. the same mass), except it has opposite charge.

Question 2

How do you recognise the symbol for an anti particle?

Answer 2

the symbol for an antiparticle includes a bar above the symbol
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Question 3

What are all leptons/antileptons and their charges?

Answer 3

Leptons
- electron -1
- electron neutrino 0

Antileptons
- antielectron/positron +1
- Electron antineutrino 0

Question 4

What are all quarks/antiquarks and their charges?

Answer 4

Quarks
- Up +2/3
- Down -1/3

Anti quarks
- Antiup -2/3
- Antidown +1/3

Question 5

What is annihilation?

Answer 5

When a particle and its antiparticle meet, they annihilate each other. This means when a particle encounters its antiparticle (e.g. an electron and a positron), all the mass is converted into energy.

Question 6

What are leptons?

Answer 6

Leptons are the lightest of the subatomic particles and they always exist separately. They do not combine to form composite subatomic particles.

Question 7

What are hadrons?

Answer 7

Unlike leptons, quarks and antiquarks do not exist separately and combine to form composite subatomic particles known as hadrons.

Question 8

What are the three types of hadrons and their composition?

Answer 8

• baryons – consists of 3 quarks -proton/neutron
• antibaryons – consists of 3 antiquarks -antiproton/antineutron
• mesons – consists of 1 quark-antiquark pair. - pions

All quarks have baryon number = +⅓, and all antiquarks have baryon number = -⅓. This means that all baryons must have baryon number = 1 and antibaryons = - 1.

Question 9

What is the charge, baryon number and quark composition of a proton?

Answer 9

Charge +1
Baryon number +1
quark composition uud

Question 10

What is the charge, baryon number and quark composition of a neutron?

Answer 10

Charge 0
Baryon number +1
quark composition udd

Question 11

What are the four pions and their composition?

Answer 11

Mesons consist of one quark and one antiquark, as a result they have a baryon number of 0
The first generation quarks and antiquarks combine to form the pions:

π+ ud- 1e

π- -ud 1e

π0 uu- 0e

π0 dd- 0e

Question 12

What is the conservation of charge law?

Answer 12

When charge is conserved through a reaction. It will be the same on one side of the equation as the other.

Question 13

What are the four fundamental forces?

Answer 13

Gravitational
electromagnetic
weak
strong

Question 14

What are the properties of gravitational force?

Answer 14

Experienced by - All matter
Range - infinite
Comments - very weak – negligible except between large objects such as planets

Question 15

What are the properties of weak force?

Answer 15

Experienced by - all leptons, all quarks
Range - very short
Comments - only significant when the e-m and strong interactions do not operate

Question 16

What are the properties of electromagnetic force?

Answer 16

Experienced by - all charged particles
Range - infinite
Comments - also experienced by neutral hadrons, as these are composed of quarks

Question 17

What are the properties of strong force?

Answer 17

Experienced by - all quarks
Range - short

Question 18

What are strong interactions?

Answer 18

Strong interactions (lifetime 10^-24s)

• Only hadrons are involved.
• There is no change in quark flavour.
• These are typically involved in collisions between particles.

Question 19

What are electromagnetic reactions?

Answer 19

Electromagnetic interactions (lifetime 10^-12-10^-18 s)

• The particles must be charged or have charged components. Although a neutron is uncharged, it consists of charged quarks.
• There is no change in quark flavour.
• One or more photons may be emitted.

Question 20

What are weak interactions?

Answer 20

Weak interactions (lifetime 10^-8 s)

• Neutral leptons (neutrinos) are involved.
• There may be a change in quark flavor.