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