OCR A Level Physics

Revision Notes

6.8.5 Quarks in Particle Decay Equations

Test Yourself

Balancing Quark transformation equations

  • By looking at the transformation of quarks inside the protons and neutrons in beta decay it is possible to analyse the decay of specific quarks inside

Beta-minus decay

  • In beta-minus decay, one of the neutrons in a nucleus is converted into a proton in a process that may be written as:

n → p + e-space v with bar on top subscript e

  • The neutron, n has the quark composition udd
  • The proton, p has the quark composition uud
  • So the beta-minus decay must involve a down quark converting to an up quark

d → u + e-space v with bar on top subscript e

6-8-5-quarks-of-beta-minus_ocr-al-physics

Balancing Charge

  • The charge on the left side of the equation is -1 third
  • The total charge on the right side is 2 over 3e + (-1)e + 0 = -1 thirde
  • So, the decay equation is balanced in terms of charge

Beta-plus Decay

  • In beta-plus decay a proton is converted into a neutron with the emission of a positron and an electron neutrino in a process that may be written as: 

p → n + e+ + v

  • The proton, p has the quark composition uud
  • The neutron, n has the quark composition udd
  • So, the beta-plus decay must involve an up quark converting to a down quark

u → d + e+ + v

6-8-5-quarks-of-beta-plus-decay_ocr-al-physics

Balancing Charge

  • The charge on the left side of the equation is +2 over 3
  • The total charge on the right side is -1 thirde + e + 0 = +2 over 3e
  • So the decay equation is balanced in terms of charge

Charge must be conserved in any reaction or decay equation

Worked example

The equation for β decay is2.3.3 Beta Minus EquationUsing the quark model of beta decay, prove that the charge is conserved in this equation.

Worked example - beta decay quarks, downloadable AS & A Level Physics revision notes

You've read 0 of your 0 free revision notes

Get unlimited access

to absolutely everything:

  • Downloadable PDFs
  • Unlimited Revision Notes
  • Topic Questions
  • Past Papers
  • Model Answers
  • Videos (Maths and Science)

Join the 80,663 Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Katie M

Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.