| Date | November 2019 | Marks available | 2 | Reference code | 19N.3.hl.TZ0.27 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Calculate | Question number | 27 | Adapted from | N/A |
Question
Nuclear medicine uses small amounts of radioisotopes to diagnose and treat some diseases.
State two common side effects of radiotherapy.
Explain why technetium-99m is the most common radioisotope used in nuclear medicine.
25.0 μg of iodine-131, with a half-life of 8.00 days, was left to decay.
Calculate the mass of iodine-131, in μg, remaining after 32.0 days. Use section 1 of the data booklet.
Markscheme
Any two of:
hair loss
fatigue
nausea
sterility
skin reaction
diarrhoea
vomiting
damage to lymph system
urinary/bladder changes
anxiety/emotional problems
joint/muscular stiffness
loss of appetite
sore/dry mouth
loss of weight
secondary cancer ✔
Any two of:
half-life is 6 hours/long enough for a scan to occur
OR
half-life short enough not to remain in body ✔
NOTE: Accept “short half-life so patient is not exposed to lots of ionizing radiation”.
decay releases «low energy» gamma rays
OR
gamma rays less likely to be absorbed by cells ✔
can form several «coordination» complexes ✔
NOTE: Accept "can exist in many oxidation states «so can form multiple complexes»" OR "chemically versatile «so can act as a tracer by bonding to several bioactive compounds»”.
«low-energy» radiation/gamma-rays can be detected by common X-ray equipment ✔
ALTERNATIVE 1
4 half-lives ✔
1.56 «μg of iodine-131 remain» ✔
ALTERNATIVE 2
m = 25.0 ✔
1.56 «μg of iodine-131 remain» ✔
ALTERNATIVE 3
λ = « » = 8.66 × 10−2 «day−1» ✔
m = « » 1.56 «μg of iodine-131 remain» ✔
Award [2] for correct final answer.
