74 lines
3.6 KiB
TeX
74 lines
3.6 KiB
TeX
\section{Experimental setup}
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\label{sec:experimental_set_up}
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This measurement is part of the AlCap experiment done at PSI, Switzerland.
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The 2015 summer run focused on the detection of neutral particles: low energy
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X-ray, gamma ray and neutron emission after the muon is captured by the
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nucleus.
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The X-rays and gamma rays of interest are:
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\begin{itemize}
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\item muonic $2p-1s$ transition in aluminum: \SI{346.8}{\kilo\eV}
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\item \SI{843.7}{\kilo\eV} gamma from the $\beta^-$ decay of \ce{^{27}Mg}
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(half-life: \SI{9.46}{\min})
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\item \SI{1808.7}{\kilo\eV} gamma from the first excited state of
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\ce{^{26}Mg}
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\end{itemize}
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Low momentum muons (less than \SI[]{40}{\mega\eVperc}) were stopped in
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a target after passing a muon counter
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(\SI{60}{\mm}$\times$\SI{60}{\mm}$\times$\SI{0.5}{\mm} plastic scintillator).
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% Upstream from the muon counter, a
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% \SI{10}{\cm} $\times$ \SI{10}{\cm} $\times$ \SI{0.6}{\cm} scintillator with
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% a \SI{40}{\mm} diameter hole cut in the center acted as a beam defining
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% veto counter to the incoming muon beam.
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There were two 5"$\times$2" liquid scintillator BC501a detectors setup on the
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beam right to detect neutrons. For gamma spectrum analysis and normalization
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we used an HPGe detector installed on the beam left. In addition, a \ce{LaBr3}
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scintillator was also tested if it would be suitable to use in the STM. A 25
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LYSO crystal array was placed downstream of the target beam left to observe
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high energy photons emitted.
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Two identical preamplifier outputs from the HPGe detector were fed into: (a)
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a timing filter amplifier for timing information, and (b) a spectroscopy
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amplifier for energy information. The timing pulses were read out by a 14-bit
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500-MS/s desktop digitizer(CAEN DT5730). In order to accommodate both low
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energy X-rays and relatively high energy gamma rays, we used two channels from
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the spectroscopy amplifier with different gain settings: (a) a lower gain
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channel for photons up to \SI{6.5}{\mega\eV}; and (b) a higher gain channel for
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photons up to \SI{2.5}{\mega\eV}. These channels were read out by a 14-bit
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100-MS/s VME digitizer (CAEN V1724).
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The \ce{LaBr3} crystal is coupled with a photomultiplier, of which output
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pulses were large enough so no further amplification was needed. This channel
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is read out with the DT5730.
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% Detectors' outputs were read out using waveform digitizers. We used a 14-bit
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% 100-MS/s VME digitizer (CAEN V1724) to record energy signals from
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% HPGe and \ce{LaBr3} detectors. There were two energy outputs from the HPGe
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% detector with different gain settings: (a) low gain channel for photons up to
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% \SI{6.5}{\mega\eV}; and (b) high gain channel for photons up to
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% \SI{2.5}{\mega\eV}. The timing signals from these detectors, and signals from
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% plastic and liquid scintillators were fed into a faster digitizer, namely
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% a 14-bit 500-MS/s desktop digitizer (CAEN DT5730).
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% These fast timing channels
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% were also read out using a multihit TDC (CAEN V1290A) as a back up solution.
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% All digitizers and TDC were synchronized by an external master clock.
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Experimental layout is shown in \cref{fig:R2015a_setup}.
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\begin{center}
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\begin{figure}[tbp]
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\centering
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\includegraphics[width=0.70\textwidth]{figs/r15a_setup_photo}
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\caption{Layout of the AlCap 2015 summer run. Muons entered from the top of
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the image. The LYSO detector is not visible in this image, which is
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located further out in the bottom of the image.}
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\label{fig:R2015a_setup}
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\end{figure}
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\end{center}
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There were several runs with different targets made of aluminum, titanium,
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lead, water. All targets were sufficiently thick to stop the muon beam with
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momenta up to \SI{40}{\mega\eVperc}.
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