Quarks in Particle Decay Equations (OCR A Level Physics) : Revision Note

Katie M

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Katie M

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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 is

2.3.3 Beta Minus Equation

Using the quark model of beta decay, prove that the charge is conserved in this equation.

Answer:

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

Author: Katie M

Expertise: Physics Content Creator

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.

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