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E = mc2 - mass energy conversion

Q3. Nuclei of Po decay by the emission of an α particle to form a stable isotope of an element X. You may assume that no γ emission accompanies the decay.

(a)

(i) State the proton number of X. Two protons come out of the nucleus in alpha decay.

84 - 2 = 82

(ii) State the nucleon number of X. Four nucleons come out of the nucleus in alpha decay.

218-4 = 214

(2 marks)

(b) Each decaying nucleus of releases 8.6 × 10–13 J of energy.

(i) State the form in which this energy initially appears.

Kinetic energy [or electrostatic potential energy]

(ii) Using only the information provided in the question, calculate the difference in mass between the original polonium atom and the combined mass of an atom of X and an α particle.

ΔE = Δmc2

Δm = ΔE/c2 = 8.6 × 10–13 / (3.0 × 108 )2

Δm = 9.6 x 10-30kg

speed of light in vacuum = 3.0 × 108 ms–1

(3 marks)

(Total 5 marks)