A hospital physicist prepares a patient for a scan using technetium-99m. At the time of injection, the activity of the sample is 320 MBq. Its half-life is 6...
Question 1 Report
A hospital physicist prepares a patient for a scan using technetium-99m. At the time of injection, the activity of the sample is 320 MBq. Its half-life is 6.0 hours. The gamma detector has a circuit in which radiation produces small pulses of current. The physicist uses the smallest suitable activity because energy from ionising radiation can damage atoms and electrons in body tissue.
(a) State what an activity of 320 MBq means. [2]
(b) Calculate the activity remaining after 18 hours. [3]
(c) Explain why the patient is advised to avoid long periods close to other people immediately after the scan. [2]
(d) Which unit is used for absorbed dose, meaning energy transferred to each kilogram of material? [1]
(e) State one difference between absorbed dose and equivalent dose. [1]
Answer Details
(a) \(320\text{ MBq}=320\,000\,000\text{ Bq}\). This means that 320 000 000 nuclear decays occur each second. [2]
(b) \[\frac{18}{6.0}=3\text{ half-lives}\]
\[320\text{ MBq}\rightarrow160\text{ MBq}\rightarrow80\text{ MBq}\rightarrow40\text{ MBq}\]
Activity remaining = \(40\text{ MBq}\). [3]
(c) After injection, the patient emits ionising gamma radiation. Reducing the time spent close to the patient reduces the radiation dose received by other people. [2]
(d) Absorbed dose is measured in grays, \(\text{Gy}\). [1]
(e) Absorbed dose is energy absorbed per unit mass. Equivalent dose also takes account of the radiation type and its biological effect. [1]
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