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Date November 2019 Marks available 2 Reference code 19N.3.hl.TZ0.27
Level HL Paper 3 Time zone TZ0
Command term Explain 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.

[1]
a.

Explain why technetium-99m is the most common radioisotope used in nuclear medicine.

[2]
b.

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.

[2]
c.

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 ✔

a.

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 ✔

b.

ALTERNATIVE 1
4 half-lives ✔
1.56 «μg of iodine-131 remain» ✔

 

ALTERNATIVE 2
m = 25.0 1232.08.00
1.56 «μg of iodine-131 remain» ✔

 

ALTERNATIVE 3
λ = « ln28.00 » = 8.66 × 10−2 «da
y−1» ✔
m = «  25.0   e 8.66 × 10 2 × 32.0 = » 1.56 «μg of iodine-131 remain» ✔

 

Award [2] for correct final answer.

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 2: Atomic structure » 2.1 The nuclear atom
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