Quark Composition (CIE A Level Physics)

State how many 'up' quarks there are in the nucleus of iron, ${}_{26}{}^{56}\mathrm{Fe}$.

Answer: 

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

The baryon Δ⁺⁺ was discovered in a particle accelerator using accelerated positive pions on hydrogen targets.

Which of the following is the quark combination of this particle?

A:        B:        C:        D:  

Answer: A

• Since it is a baryon, its made up of three quarks
  • This rules out option C
• Baryons are made up of 3 quarks
• Anti-baryons are made up of 3 anti-quarks
  • This rules out option B
  • There cannot be a combination of quarks and anti-quarks
• The baryon Δ⁺⁺ has a charge of 2+
• Adding up the charges of quarks
  • A:  
  • D:    
• Therefore, the correct combination is option A