a) Draw a diagram to represent the structure of a neutral helium atom. Clearly label the components. Taking the mass of the smallest component to be 1 'unit', what are the approximate masses of the other components? (8 marks) X 234 b) Th + He 2 The equation above represents a nuclear decay. i) What is the value of the mass number (represented by X) of the uranium? 234 ii) Write down the symbol for a nuclide which is an isotope of thorium - 234 ( Th) 90 iii) The thorium nuclide (Th) is not stable. It decays by (B-emission) to produce protactinium (symbol Pa). Represent this reaction in an equation like the one above. (7 marks) c) The half-life for the decay of Thorium-234 is 24 days. The Physics Department of the U.W.I, in Jamaica bought a sample of this thorium from England. On the day of despatch its activity was 4 x 10' Bq (i.e. 4 x 105 disintegrations per second). i) What was the activity of the source when it arrived in Jamaica 72 days later? ii) What safety precautions should the suppliers have taken to ensure that none of the dock workers could be harmed? State any two