Why does primordial nucleosynthesis end about 3 minutes after the Big Bang? Select one: a. The number densities of photons is too large at this time and the photons induce fission, stopping nuclei formation b. The universe is too hot at t-3 minutes C. The number densities of neutrons and protons and other nuclei are too small at this time and fusion fades out. O d. Deuterium has a lifetime of 3 minutes, so after this time no more deuterium survives as it decays away.

I. When first discovered, α, β and γ radioactivity were referred to as α-rays, βrays and γ-rays. Now we refer to α-particles and β-particles, but still use theterm γ-rays. What type of particles are α and β commonly known as? What is γ commonly known as? II. What is the mass (calculate both in kg and unified mass units, u) of the α -particle? What is the mass (calculate both in kg and unified mass units, u) ofthe β -particle? Which particle (α or β) is more massive? Which particle has agreater amount of charge (α or β)? Which particle (α or β) would you expect topenetrate further into a piece of lead?

Referring to the Feynman diagram, name:a. particle A b. the exchange particle involved c. the force involved in the interaction d. Explain how you know that there has not been a change of quark colour but there has been a change of flavour.

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