| Date | May 2016 | Marks available | 1 | Reference code | 16M.3.sl.TZ0.13 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 13 | Adapted from | N/A |
Question
Fusion and fission reactions are important nuclear reactions.
Curium, \({}^{240}{\rm{Cm}}\), was synthesized by bombarding thorium nuclei, \({}^{232}{\rm{Th}}\), with carbon-12 nuclei. State a balanced equation for this reaction.
Uranium-235 has a half-life of 7.038×108 years.
(i) Determine the time required for the mass of \({}^{235}{\rm{U}}\) in a sample originally containing 1.000 g of \({}^{235}{\rm{U}}\) to decrease to 0.125 g.
(ii) Outline why products of the fission of uranium-235 must be disposed of carefully.
Outline why an element such as thorium, Th, usually undergoes nuclear fission, whereas helium, He, undergoes nuclear fusion.
Markscheme
\[{}_{90}^{232}{\rm{Th}} + {}_6^{12}{\rm{C}} \to {}_{96}^{240}{\rm{Cm}} + 4{}_0^1{\rm{n}}\]
Accept \({}^{232}{\rm{Th}} + {}^{12}{\rm{C}} \to {}^{240}{\rm{Cm}} + 4{\rm{n}}\).
Accept ”4n” for “\(4{}_0^1{\rm{n}}\)” in any equation.
(i)
«3 half-lives, so» 2.11 × 109 «years»
Accept any value within range 2.11–2.13 × 109 «years».
(ii)
products are radioactive/undergo «nuclear» decay
OR
products have unstable nuclei
OR
products may be used to make «nuclear» weapons
both processes increase «nuclear» binding energy per nucleon
OR
both processes bring product closer to the maximum binding energy per nucleon «of iron-56»
OR
both processes result in more stable nuclei
Mark can be awarded to an annotated sketch of binding energy per nucleon vs A.
