5.3.2 Fundamental Particles. (a) explain that since protons and neutrons contain charged...

5.3.2 Fundamental Particles

(a) explain that since protons and neutrons contain charged constituents called quarks they are, therefore, not fundamental particles

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Until mid-20th century, it was though that all atoms consisted of electrons, protons and neutrons

Due to the increasing sophistication of the particle accelerator, and increased sensitivity of equipment measuring cosmic rays, more and more particles were being discovered

Eventually, this “particle zoo” was arranged in a more orderly way

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Fundamental Particles

CERN Standard model

(b) describe a simple quark model of hadrons in terms of up, down and strange quarks and their respective antiquarks, taking into account their charge, baryon number and strangeness;

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Atom

Hadrons Leptons

Electrons

NeutrinosProtons

Neutrons

Quarks

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(d) describe the properties of neutrons and protons in terms of a simple quark model

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ProtonNeutron

u d d u u d

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Proton uud total charge = ⅔ + ⅔ - ⅓ = 1

Neutron udd total charge = ⅔ - ⅓ - ⅓ = 0

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(e) describe how there is a weak interaction between quarks and that this is responsible for β decay

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Nucleus is held together by the strong nuclear force

This explains α decay, but not β decay There is another force, the weak interaction or

weak nuclear force Acts on quarks and leptons Responsible for β decay

(f) state that there are two types of β decay

(i) state that a β- particle is an electron and a β+ particle is a positron

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There are two types of β decay:

Beta-minus (β-) electron negative charge –e

Beta-plus (β+) positron positive charge +e

(g) describe the two types of β decay in terms of a simple quark model;

(h) state that (electron) neutrinos and electron) antineutrinos are produced during β+ and β- decays, respectively

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In β- decay a neutron is changed into a proton, in other words udd changes into uud. A d changing to a u can only happen through the weak interaction.

Electron Anti-neutrino

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In β+ decay a proton is changed into a neutron, in other words uud changes into udd. A u changing to a d can only happen through the weak interaction.

Electron neutrino