# 13.2.2 Quark Composition

### Quark Composition: Protons & Neutrons

• Protons and neutrons are not fundamental particles. They are each made up of three quarks
• Protons are made up of two up quarks and a down quark
• Neutrons are made up of two down quarks and an up quark

Protons and neutrons are made up of three quarks

• You will be expected to remember these quark combinations for exam questions

#### Worked example

• Step 1: Calculate number of protons:
• The number of protons is from the proton number = 26 protons
• Step 2: Calculate number of neutrons:
• The number of neutrons = nucleon number – proton number = 56 – 26 = 30 neutrons
• Step 3: Up quarks in a proton:
• Protons are made up of uud quarks = 2 up quarks
• Step 4: Up quarks in a neutron:
• Neutrons are made up of udd quarks = 1 up quark
• Step 5: Total number of up quarks:
• 26 protons x 2 up quarks = 52 up quarks
• 30 neutrons x 1 up quark = 30 up quarks
• 52 + 30 = 82 up quarks

### Quark Composition: β– & β+ decay

• Beta decay happens via the weak interaction
• This is one of the four fundamental forces and it’s responsible for radioactive decays

#### Quark Composition: β– decay

• Recall that β decay is when a neutron turns into a proton emitting an electron and anti-electron neutrino
• More specifically, a neutron turns into a proton because a down quark turning into an up quark

Beta minus decay is when a down quark turns into an up quark

#### Quark Composition: β+ decay

• Recall that β+ decay is when a proton turns into a neutron emitting an positron and an electron neutrino
• More specifically, a proton turns into a neutron because an up quark turns into a down quark

Beta minus decay is when an up quark turns into a down quark

### Author: Ashika

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