Quark Compositions (Cambridge (CIE) AS Physics)

State how many 'up' quarks there are in the nucleus of iron, .

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

Remembering quark combinations is useful for the exam. However, as long as you can remember the charges for each quark, it is possible to figure out the combination by making sure the combination of quarks add up to the charge of the particle (just like in the worked example)