| Date | May 2017 | Marks available | 1 | Reference code | 17M.3.hl.TZ2.26 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Calculate | Question number | 26 | Adapted from | N/A |
Question
Targeted Alpha Therapy (TAT) is a technique that involves using alpha-radiation to treat leukemia and other dispersed cancers.
Yttrium-90 and lutetium-177 are used in radiotherapy.
Explain why alpha-radiation is particularly suitable for this treatment.
Outline how the alpha-radiation in TAT is directed to cancer cells.
Identify the type of radiation emitted by these two radioisotopes.
State an equation for the one-step decay of yttrium-90.
The half-life of lutetium-177 is 6.75 days. Calculate the percentage remaining after 27 days.
Markscheme
more damaging than other radiation types
OR
very damaging to «cancer» cells
OR
high ionizing density «of alpha particles»
absorbed within a very short range of emission
OR
causes little damage to surrounding tissues
Accept “high ionizing power «of alpha particles»” for M1.
Accept “low penetrating power «of alpha particles»” for M2.
[2 marks]
«radioactive isotope/radionuclide/alpha-emitter» administered using carrier drug/protein/antibodies
[1 mark]
beta/β «radiation»
[1 mark]
\({}_{39}^{90}Y \to {}_{40}^{90}Zr + \beta \)
Accept "\(_{ - 1}^{\;\,0}e/e/{e^ - }\)" OR "\(_{ - 1}^{\;\,0}\beta /{\beta ^ - }\)"
Accept ECF from (b) (i) if incorrect radiation identified, eg, \(_{39}^{90}Y \to _{37}^{86}Rb + _2^4He\)
[1 mark]
ALTERNATIVE 1:
«4 half-lives»
6.25 «%»
ALTERNATIVE 2:
«Nt = N0\({\left( {0.5} \right)^{\frac{t}{{{t_{1/2}}}}}} = 100{\left( {0.5} \right)^{\frac{{27}}{{6.75}}}} = \)» 6.25 «%»
[1 mark]
