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Solutions: Atomic Structure

Q10.

(a) Give the number of nucleons and the number of electrons in an atom of Nas.

22 (nucleons)
11 (electrons)

(2)

(b) The isotope s is a positron emitter. In positron emission an up quark undergoes the following change:

u s d + e+ + ve

Show that charge, lepton number and baryon number are conserved in this decay.

charge: +2/3 = -1/3 + 1 + 0 lepton number: 0 = 0 - 1 + 1 baryon number: 1/3 = 1/3 + 0 + 0

(3)

(c) Describe what happens when a positron collides with an electron.

When a positron and electron collide the electron and the positron are annihilated. Two gamma photon(s)/ ray(s) are produced
as the masses of the particles are converted into electromagentic energy (Maximum of 2 marks)

(2)
(Total 7 marks)