| Date | November 2018 | Marks available | 2 | Reference code | 18N.3.hl.TZ0.22 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 22 | Adapted from | N/A |
Question
Nuclear isotopes are used in the treatment of cancer.
Gamma radiation is also used in radiotherapy.
Alpha particles are more damaging to human cells than any other nuclear radiation and yet they are used in targeted alpha therapy (TAT).
Explain how TAT is relatively safe to use in the treatment of dispersed cancers.
Technetium-99m () has a half-life of 6.0 hours. Calculate the percentage of remaining in a sample of the radioisotope after two days.
Suggest why the percentage of technetium-99m remaining in the human body two days after injection will be lower than that calculated in (b)(i).
Markscheme
«alpha emitter» carried to/selectively absorbed by cancer cells «by antibody, carrier drug, protein» ✔
low penetrating power
OR
short range ✔
Do not accept just “targets cancer cells and does not affect healthy cells”.
ALTERNATIVE 1:
« =» 8 /8 half-lives «required» ✔
% remaining = «(0.5)8 × 100 =» 0.39 «%» ✔
ALTERNATIVE 2:
λ = « =» 0.1155 ✔
% remaining = «100 × e–0.1155 × 48 =» 0.39 «%» ✔
Award [2] for correct final answer.
Accept “0.32 «%»” in ALTERNATIVE 2.
removed by excretion ✔
Accept any method of excretion.
