| Date | May 2019 | Marks available | 2 | Reference code | 19M.3.hl.TZ2.26 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Evaluate | Question number | 26 | Adapted from | N/A |
Question
Technetium-99m, Tc-99m, is a gamma-ray emitter commonly used as a medical tracer.
Its half-life is 6.0 hours.
Evaluate the suitability of technetium-99m for this use.
Calculate the percentage of technetium-99m remaining after 10.0 hours. Use section 1 of the data booklet.
Markscheme
Any two of:
can be readily “tagged” to variety of biologically active carriers «which will deliver it to specific locations for imaging uses» [✔]
frequency of radiation is compatible with existing X-ray detection apparatus [✔]
product of decay has low radioactivity/relatively short half-life/low total exposure to patient [✔]
«but small» increased risk of cancer to patient [✔]
must be made on site [✔]
Note: Accept other valid answers outlining advantages or limitations of Tc-99m, such as “produces only LLW”, “Tc is a transition element forming compounds in a variety of oxidation states”, “gamma-radiation «can escape the body and» be detected by external sensors”, “activity decreases quickly, so dose must be calculated prior to each injection”.
ALTERNATIVE 1
[✔]
31 «% remaining» [✔]
ALTERNATIVE 2
λ «= »= 0.1155 hours–1 [✔]
« × 100 = e–λt ×100 = 0.31498 × 100»
31 «% remaining» [✔]
Note: M1 is for correct substitution of values.
Award [2] for correct final answer.
Examiners report
The most frequent response was the short half-life, followed by the emission and detection of gamma radiation.
Most candidates were able to calculate the percentage of technetium-99m correctly.
