\subsubsection{Additional timing and energy results for 30mm}
In the coincidence apparatus measurements additional properties are recorded; namely the delay peak centroid, the light output and the energy resolution. In figure \ref{fig:centroidposition} the shift in the delay peak position with increasing DOI is plotted. It can be seen that a plateau is reached for both configurations at 20 mm. In \cite{Moses_Derenzo_1999} this plateau is attributed to the travel time between photons travelling `towards' and `away' from the photodetector approaching equality. As the electronic trigger from the discriminator is tuned as close to the beginning of the signal as possible this cannot come before generated light has physically travelled from its emission position to the photodetector. This is supported by the total shift seen of 150 ps to 370 ps corresponding to an approximate physical distance of 30 mm in L(Y)SO.
