Mark S. Brown edited 20mm Measurements.tex  over 10 years ago

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In figure \ref{fig:confinement-20} the confinement is consistent across all DOI except for the unwrapped configuration. In this case we see a gradual drop off in the number of $\gamma\gamma$ events recorded with increasing DOI. This is due to poor vertical alignment. Due to this, the confinement region lies to the side of the scintillator crystal at higher DOI not within it. In figure \ref{fig:ctrdoi-20} we see that this results in an increasingly larger error in the CTR until not enough events are collected to accurately determine the value at all. Even so, we find that poor alignment whilst degrading the error in the measurement, does not introduce a systematic shift into the CTR. Thus as long as the number of $\gamma\gamma$ events collected is high then alignment is not a critical parameter.   In figure \ref{fig:ctrdoi-20} we see the CTR improves (as in decreases) with increasing amounts of wrapping by 20ps; from unwrapped, to partially wrapped and finally to  wrapped. This is due to increased light output as seen in figure \ref{fig:lightoutput-20}. These measurements have lower individual CTR errors than the previous 30mm measurements,  likely due to a greater number of $\gamma\gamma$ events recorded; recorded. These being  namely 5000 for LSO:CeCa compared to 3400 for LYSO:Ce. In [figure 8] \cite{r_Paganoni_Pauwels_et_al__2011} a CTR As the volume  of 210ps scintillator crystal  isseen for  the $2\times2\times20$mm$^3$ LSO:CeCa scintillator crystal. We also see same in both measurements this difference is primarily due to  the difference in measurement time. The wrapped  CTR is $198\pm2$ps compared to 176$\pm$7ps  for the standard coincidence measurement given in [Table 2]\cite{uffray_Jarron_Meyer_Lecoq_2014}. For  an equivalent $2\times2\times20$mm$^3$ LYSO:Ce scintillator crystal is a CTR of  202.7$\pm$4.0ps in standard coincidence. Compared to the values given in table \ref{tab:doictrresults-20} coincidence is observed. Therefore  we see an equivalent value for that LSO:CeCa is a superior material to that of LYSO:Ce. We also see that  the wrapped configuration.     In CTR is worse in  thewrapped  DOI measurement we see a value of 198.3$\pm$4.4ps. In timing coincidence apparatus than in the standard. This conclusion is in agreement with  the 30mmLYSO  measurements where  we see values of 225.0$\pm$3.1ps for the standard coincidence to 239$\pm$4ps in the DOI coincidence apparatus.Both measurements indicate no improvement to the CTR, within error, is expected for inclusion of confinement information.