Topic Menu

Cyber-chess a chess instruction site

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 marks)

(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 marks)

(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 marks)
(Total 7 marks)