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Solutions: Radioactivity Questions

Q3.

(a) Nuclear fission can occur when a neutron is absorbed by a nucleus of uranium-235. An incomplete equation for a typical fission reaction is given below.

(i) State the nuclear composition of X.

proton number = 36

neutron number = 56

(ii) Name the element of which X is an isotope.

Krypton

(3 marks)

(b) In a small nuclear power plant one fifth of the fission energy is converted into a useful output power of 10 MW. If the average energy released per fission is 3.2 × 10–11J, calculate the number of uranium-235 nuclei which will undergo fission per day.

It is only operating at one-fifth efficiency so

total output = 10 × 5 = 50 MW

energy in one day = 50 × 106 × 24 × 3600 J = 4.32 × 1012 J

fission atoms per day = 4.32 × 1012 /3.2 × 10–11

= 1.35 ×1023

(3 marks)

(Total 6 marks)