(a(i))[1]
State what is meant by a tracer.
(a(ii))[2]
State the symbol of the particle represented by $X$ and the values of $P$, $Q$ and $R$. $X:$ $P:$ $Q:$ $R:$
(b(i))[2]
Explain how the radioactive decay of fluorine-18 causes gamma-ray photons to be emitted from the body and detected during a PET scan.
(b(ii))[2]
Explain how the detection of the gamma-ray photons is used to produce an image of the tissue being examined.
(c(i))[3]
The half-life of fluorine-18 is $T$. A patient is injected with amount $n$ of substance of fluorine-18. Determine an expression for the initial value $R_0$ of the rate $R$ of production of gamma-ray photons by the tracer, in terms of $n$, $T$ and the Avogadro constant $N_A$.
(c(ii))[2]
On Fig. 9.1, sketch how $R$ varies with time $t$.