add progress14

progress14/NeutronAnalysis.tex

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+ In R2013, two BC501 neutron
+counters ($5''$ diameter  and $5''$ depth) were borrowed from the
+MuSun experiment, and placed outside the vacuum chamber on
+both sides of the muon beam and centred on the stopping
+target. Neutron spectra between 1 to about 20 MeV were obtained.  The lower
+threshold is limited by pulse shape discrimination (PSD) which
+identifies neutron from photon events.  Calibration of the detector
+energy primarily used Cs-137 and Co-60, however these sources proved
+inadequate. The Cs-127 Compton edge was too low in energy to be useful
+and the Co-60 has two overlapping Compton edges. An average of the
+two edge energies was used for calibration. An AmBe source was
+originally intended to provide a known neutron spectrum and it did prove
+useful in providing a 4.19 MeV gamma line for calibration. A ratio of the fast to slow
+integrated waveform components  
+was used to provide neutron/gamma discrimination. 
+Discrimination is excellent above 1 MeVee, Figure~\ref{psdplot_2013}. 
+Analysis of the R2013 data demonstrated that a waveform digitiser of
+at least 250 MHz sampling rate is needed to optimise the pulse shape
+discrimination.  A raw neutron spectrum is shown in Figure
+~\ref{neutron_spectrum}. Initial work on unfolding the
+spectrum has begun and is described in a later section. \\
+
+\begin{figure}[btp] 
+	\centering
+	\includegraphics[width=0.55\textwidth]{figs/PSD1} 
+	\caption{Pulse shape discrimination between
+    neutrons (top band)  and gammas (bottom band). The true neutron
+    energy is approximately twice the energy deposited in
+    MeVee.} \label{psdplot_2013}
+\end{figure} 
+
+
+\begin{figure}[btp] 
+	\centering
+	\includegraphics[width=0.55\textwidth]{figs/Neutron_Spectrum} 
+	\caption{Raw neutron spectrum from an $Al$
+          target. The horizontal axis is electron equivalent energy
+          which is approximately a factor of 2 greater than the recoil
+          proton energy, which is of course folded by the detector
+          response function. \label{neutron_spectrum}. }
+\end{figure} 
+
+