SL Paper 2
This question is about radioactivity.
Caesium-137 \(\left( {{}_{55}^{137}{\rm{Cs}}} \right)\) is a radioactive waste product with a half-life of 30 years that is formed during the fission of uranium. Caesium-137 decays by the emission of a beta-minus (β–) particle to form a nuclide of barium (Ba).
State the nuclear equation for this reaction.
Determine the fraction of caesium-137 that will have decayed after 120 years.
Explain, with reference to the biological effects of ionizing radiation, why it is important that humans should be shielded from the radiation emitted by caesium-137.
This question is in two parts. Part 1 is about nuclear reactions. Part 2 is about thermal energy transfer.
Part 1 Nuclear reactions
Part 2 Thermal energy transfer
(i) Define the term unified atomic mass unit.
(ii) The mass of a nucleus of einsteinium-255 is 255.09 u. Calculate the mass in MeVc–2.
When particle X collides with a stationary nucleus of calcium-40 (Ca-40), a nucleus of potassium (K-40) and a proton are produced.
\[{}_{20}^{40}{\rm{Ca + X}} \to {}_{19}^{40}{\rm{K + }}{}_1^1{\rm{p}}\]
The following data are available for the reaction.
(i) Identify particle X.
(ii) Suggest why this reaction can only occur if the initial kinetic energy of particle X is greater than a minimum value.
(iii) Before the reaction occurs, particle X has kinetic energy 8.326 MeV. Determine the total combined kinetic energy of the potassium nucleus and the proton.
Potassium-38 decays with a half-life of eight minutes.
(i) Define the term radioactive half-life.
(ii) A sample of potassium-38 has an initial activity of 24×1012Bq. On the axes below, draw a graph to show the variation with time of the activity of the sample.
(iii) Determine the activity of the sample after 2 hours.
(i) Define the specific latent heat of fusion of a substance.
(ii) Explain, in terms of the molecular model of matter, the relative magnitudes of the specific latent heat of vaporization of water and the specific latent heat of fusion of water.
A piece of ice is placed into a beaker of water and melts completely.
The following data are available.
Initial mass of ice = 0.020 kg
Initial mass of water = 0.25 kg
Initial temperature of ice = 0°C
Initial temperature of water = 80°C
Specific latent heat of fusion of ice = 3.3×105J kg–1
Specific heat capacity of water = 4200 J kg–1K–1
(i) Determine the final temperature of the water.
(ii) State two assumptions that you made in your answer to part (f)(i).