| Date | November 2020 | Marks available | 1 | Reference code | 20N.3.hl.TZ0.17 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | State | Question number | 17 | Adapted from | N/A |
Question
Technetium-99m is the most commonly used isotope for diagnostic medicine.
State the type of radiation technetium-99m emits.
Discuss the properties that make a radioisotope suitable for diagnosis.
Describe the proper disposal of low-level radioactive waste in hospitals.
Technetium-99m has a half-life of hours. Calculate the amount of of technetium-99m remaining after hours.
Markscheme
gamma/ ✔
Any three of:
«easily» detected/traced
OR
«gamma-radiation of approximately» same frequency as X-rays «so can be detected using existing X-ray equipment» ✔
short/intermediate half-life «hence does not remain in body for long time» ✔
weak ionizing radiation «less harmful»
OR
low amount of radiation produced «so less harmful»
OR
energy of photons is low ✔
form «variety of» compounds that are absorbed by «different» organs
OR
«chemically» binds to many biologically active compounds ✔
excreted quickly «from body» ✔
store until material becomes inactive/radiation levels drop ✔
dispose with other waste
OR
dispose in landfills ✔
Only award M2 if M1 correct.
Accept “dispose by incineration” for M2.
Alternative 1:
✔
✔
Alternative 2:
✔
✔
Award [2] for correct final answer.
Examiners report
This question was well answered. Most were able to state that gamma radiation is emitted from technetium-99m. The most common incorrect answer was beta radiation.
Some excellent answers were seen for this question; often candidates were hitting four of the assigned marking points, though a few candidates confused diagnosis and radiotherapy. Nearly everyone got a mark for "short half-life", however. This question was much better answered than in previous sessions.
Surprisingly, this question caught out several candidates and the marks varied from zero to one to two. To score full marks, candidates first had to state that the proper disposal of low-level radioactive waste (LLW) in hospitals involves storing the material until such time as radiation levels drop. Then the material can be disposed of in landfills for example. A number failed to outline the first point and some also mixed up LLW with HLW.
The question on half-life was very well answered and nearly all scored full marks, often via different methods of calculation of the amount of technetium-99m remaining after a period of 48 HRS.
