Problem 1

Molecular imaging is a powerful tool in medical diagnostics. The nuclear isomer

^{99m}\ce{Tc}

(m = metastable) is an excellent γ-emitter (

t_{1/2} = 6.015

h) obtained by β− decay of a mother nuclide in a technetium generator as

[^{99m}\ce{TcO4}]^-

. (a) Identify the mother nuclide A and the emitted particle B in

\ce{A -> ^{99m}Tc + B}

. (b) An eluate from a

^{99m}\ce{Tc}

generator has an activity of 12.5 GBq (1 GBq =

10^{9}

decays per second). Calculate how many moles of

^{99m}\ce{Tc}

are present. (c) For standard imaging about 200 MBq are administered to a patient. Assuming no activity is lost through excretion, calculate how many hours the patient has to wait until the injected activity decreases to under 1% of the starting activity.

Step 1 of 3: Mother nuclide

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^{99}\ce{Mo} \rightarrow {}^{99m}\ce{Tc} + \beta^{-}\ (+\bar{\nu})

Analysis

In β− decay a neutron turns into a proton, so the daughter has the same mass number and $Z$ increased by one: $^{99}\ce{Mo}$ ( $Z=42$ ) decays to $^{99m}\ce{Tc}$ ( $Z=43$ ) emitting an electron. In the generator the parent travels as molybdate $[^{99}\ce{MoO4}]^{2-}$ and elutes as pertechnetate $[^{99m}\ce{TcO4}]^{-}$ .