3.2.1.5 Particles and Radiation: Classification of particles

Question 1

What are hadrons?

Answer 1

The only particles that can feel the strong nuclear force.
They are not fundamental particles.
Made up of smaller particles called quarks.
Two types; baryons and mesons (classified according to the number of quarks that makes them up)

Question 2

What are the properties baryons?

Answer 2

All baryons (except a free proton) can be unstable - meaning that all baryons decay to become other particles. The particle a baryon decays into depends on what it started as.

Question 3

What is baryon number?

Answer 3

A quantum number that must be conserved - basically the number of baryons
Baryons have baryon number 1
Antibaryons have baryon number -1
Other particles have baryon number 0

Question 4

What happens to the baryon number in a particle interaction?

Answer 4

The total baryon number in any particle interaction never changes

Question 5

What causes beta decay?

Answer 5

Weak interaction

Question 6

Describe neutron decay

Answer 6

n -> p + e- + electron antineutrino

Question 7

When does beta-minus decay happen?

Answer 7

When there are many more neutrons than protons in the nucleus

Question 8

What are mesons?

Answer 8

Interact with baryons via the strong force.
All mesons are unstable and have baryon number 0.
You can get loads of mesons in high energy particle collisions.
Made up of a quark and antiquark
A type of baryon

Question 9

What are some types of mesons?

Answer 9

Pions
Kaons
Others

Question 10

What are kaons?

Answer 10

Heavier and more unstable versions of pions. They have a very short lifetime and decay into pions.

Question 11

What are pions?

Answer 11

The lightest mesons. The pi- meson is the antiparticle of the pi+ meson. They are the exchange particles of the strong nuclear force.

Question 12

What are cosmic ray showers?

Answer 12

High energy particles from space, they are constantly hitting the Earth and often interact with molecules in the atmosphere to produce showers of lots of high energy particles. The tracks of these particles can be observed with a cloud chamber.

Question 13

How can cosmic ray showers be detected?

Answer 13

Using two Geiger counters placed one above the other, separated by absorbing lead. If both detect radiation simultaneously, its likely that a particle from a cosmic ray shower has been detected

Question 14

What are leptons?

Answer 14

Fundamental particles.
Don’t feel strong nuclear force.
Only interact with other particles via weak interaction.

Question 15

What are muons?

Answer 15

Fat electrons - they are unstable and eventually decay into ordinary electrons (stable)

Question 16

What are neutrinos?

Answer 16

Have (almost zero mass) and zero electric charge.
Only take part in weak interactions

Question 17

What is lepton number?

Answer 17

A quantum number that must be conserved.

Question 18

What particle is the only stable baryon?

Answer 18

Proton

Question 19

What are strange particles?

Answer 19

Created via strong force interaction, in which strangeness is conserved.
The conservation of strangeness means that strange particles means that strange particles can only be created in pairs.

Question 20

What is strangeness?

Answer 20

A quantum number.

Question 21

What is the strangeness of all leptons?

Answer 21

0

Question 22

How do strange particles decay?

Answer 22

Through weak interaction
- strangeness is not conserved in weak interaction