| Date | May 2017 | Marks available | 1 | Reference code | 17M.3.hl.TZ1.29 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | 29 | Adapted from | N/A |
Question
Nuclear radiation is dangerous because of its ability to damage cells but it can also be used in nuclear medicine.
Iodine-131 is released in nuclear explosions but is used in scanners for thyroid cancer. The half-life of iodine-131 is 8.02 days.
Yttrium-90 is used in treating certain cancers.
Formulate a nuclear equation for the beta decay of yttrium-90.
Lutetium-177 is a common isotope used for internal radiation therapy.
Suggest why lutetium-177 is an ideal isotope for the treatment of certain cancers based on the type of radiation emitted.
Calculate the rate constant, , in day−1, for the decay of iodine-131 using section 1 of the data booklet.
Calculate the time, in days, for 90% of the sample to decay.
A breathalyser measures the blood alcohol content from a breath sample. Formulate half-equations for the reactions at the anode (negative electrode) and the cathode (positive electrode) in a fuel cell breathalyser.
Markscheme
90Y → 90Zr + β–
Accept β, e or e–.
Accept 90Y → 90Zr + β– + v
[1 mark]
beta-radiation/emission AND targets tumour/cancer cells
OR
beta-radiation/emission AND limited damage to healthy cells/tissues
OR
beta-radiation/emission AND produces «small amount of» gamma-rays «for visualizing tumours/monitoring treatment»
[1 mark]
«day−1»
[1 mark]
ALTERNATIVE 1:
«N0 = initial amount = 100%»
N «= 100 – 90» = 10% at time t
«»
«» 26.7 «days»
Accept 26.6 or 27 «days»
Award [2] for correct final answer.
ALTERNATIVE 2:
«Nt = N0(0.5)n where n = number of half-lives»
10 = 100(0.5)n
«»
«»
«t » 26.6 «days»
Accept 26.7 or 27 «days»
Award [2] for correct final answer.
[2 marks]
Anode (negative electrode): C2H5OH + H2O → CH3COOH + 4H+ + 4e–
Cathode (positive electrode): O2 + 4H+ + 4e– → 2H2O
[2 marks]
