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%\title[GEANT4/EGS5]{GEANT4/EGS5}

\title{Neutron detector LDRD}

\author{Sho Uemura}
%\institute{bumming around}
\date[October 2, 2017]

%\titlegraphic{
%\includegraphics[height=0.1\textheight]{SLAC_Logo}\hspace*{4.75cm}~
%\includegraphics[height=0.1\textheight]{partner_logo_v2}
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\begin{document}

\begin{frame}
    \titlepage
\end{frame}

\begin{frame}{Can we build a directional neutron detector?}
    \begin{itemize}
        \item Sensitive in the 1-10 MeV range (``fission neutrons'')
        \item Event-by-event reconstruction of the direction of incident neutrons
        \item Good rejection of background (gammas, ambient neutrons)
        \item Other considerations:
            \begin{itemize}
                \item Efficiency, field of view
                \item Cost and scalability
                \item Portability
            \end{itemize}
        \item Outline:
            \begin{itemize}
                \item Neutron detection applications
                \item Theory
                \item Prior art
                \item What we can do
            \end{itemize}
    \end{itemize}
\end{frame}

\begin{frame}{Applications}
    \begin{itemize}
        \item Detecting/locating SNM (\url{http://aip.scitation.org/doi/full/10.1063/1.3503495})
            \begin{itemize}
                \item Plutonium emits neutrons: spontaneous fission or $(\alpha,n)$ reactions
                \item HEU is hard to detect passively, but active neutron interrogation (neutron beam and neutron detector) can work
            \end{itemize}
        \item Particle physics? astrophysics? any ideas?
    \end{itemize}
\end{frame}

\begin{frame}{Theory}
    \begin{center}
        \includegraphics[width=0.3\textwidth]{cross_sections.jpeg}
        \includegraphics[width=0.3\textwidth]{jeff_diagram.png}
    \end{center}
    \begin{itemize}
        \item In the MeV range, the biggest cross section is elastic scattering on hydrogen
        \item You can't directly measure the scattered neutron, so you need to detect multiple recoils and use some combination of scatter position, recoil proton energy, recoil proton direction, neutron time of flight
        \item One combination that works: first and second scatter positions, first recoil proton's energy and direction, neutron time of flight
        \item Good reference: Jeff's paper, \url{http://arxiv.org/abs/1210.8218}
    \end{itemize}
\end{frame}

\begin{frame}{Czech group: scintillator-pixel sandwich}
    \begin{center}
        \includegraphics[width=0.2\textwidth]{czech_concept.png}
        \includegraphics[width=0.4\textwidth]{czech_design.png}
    \end{center}
    \begin{itemize}
        \item Several papers from this group, see \url{http://ieeexplore.ieee.org/document/5873769/} and \url{iopscience.iop.org/article/10.1088/1748-0221/8/01/C01021}
        \item Concept: stack of thin plastic scintillators and silicon pixels, get two scatters
        \item Scintillators are used for trigger, could also measure proton energy; pixels measure scatter position, proton energy and in-plane direction
        \item Reconstruct event plane for the first scatter, determine source direction as the intersection of event planes
        \item Limitations: hard to scale up and get good efficiency, no event-by-event direction, fundamental problem with length scales (neutron mean free path >> proton range)
    \end{itemize}
\end{frame}

\begin{frame}{Various groups: scintillating fibers}
    \begin{center}
        \includegraphics[width=0.3\textwidth]{sandia_concept.png}
        \includegraphics[width=0.3\textwidth]{sandia_design.png}
        \includegraphics[width=0.3\textwidth]{sontrac_design.png}
    \end{center}
    \begin{itemize}
        \item \url{https://doi.org/10.1016/S0168-9002(03)01015-5}, \url{http://prod.sandia.gov/techlib/access-control.cgi/2005/056255.pdf}
        \item Concept: block of scintillating fibers
        \item Limitation: need to scale up to get efficiency
    \end{itemize}
\end{frame}

\begin{frame}{BNL: two scintillator walls}
    \begin{center}
        \includegraphics[width=0.3\textwidth]{bnl_concept.png}
        \includegraphics[width=0.3\textwidth]{bnl_design.png}
        \includegraphics[width=0.3\textwidth]{bnl_result.png}
    \end{center}
    \begin{itemize}
        \item \url{https://www.bnl.gov/isd/documents/32899.pdf}
        \item Concept: two walls of thick plastic scintillators (with double-ended readout for full position reconstruction), get a scatter in each
        \item Front wall measures first recoil proton energy, second wall gives neutron TOF and direction
        \item Reconstruct ``projected cone'' for the incident neutron, determine the source direction using overlaps
        \item Limitations: no event-by-event direction
    \end{itemize}
\end{frame}

\begin{frame}{Various groups: TPC}
    \begin{center}
    \end{center}
    \begin{itemize}
        \item Two strategies: hydrogen elastic scatters and helium-3
        \item TPC tracks give direction and energy for recoil products
        \item Hydrogen: most groups look for single scatters, in which case you only get a projected cone for the incident neutron
        \item Helium-3 $(n,p)$ reaction produces a fully reconstructable final state (both particles are charged), but He-3 is expensive and the cross section is lower than hydrogen
        \item Limitations: not portable, need high density or large volume for good efficiency
    \end{itemize}
\end{frame}

\begin{frame}{What we can do: hybrid detector}
    \begin{center}
    \end{center}
    \begin{itemize}
        \item Getting proton direction from first scatter is hard; detectors that do this are hard/expensive to scale up, and efficiency to get two scatters goes as size$^2$ so a small detector performs very poorly
        \item Time of flight is nice --- you only need position+time from the second detector, and these neutrons are nonrelativistic (<0.15 $c$) so you don't need amazing timing
        \item So: use different technologies for front and back detectors
            \begin{itemize}
                \item Front: scintillator-pixel sandwich is attractive because with 50 $\mu$m ALPIDE and thin scintillators (150-250 $\mu$m is available) it may be possible to track a recoil proton in two ALPIDEs --- ALPIDE is the ideal detector for this application
                \item Back: wall of scintillator bars --- either apply our experience with WLS-SiPM detectors, or borrow somebody's neutron wall
            \end{itemize}
        \item Efficiency now scales linearly with cost, since the wall can be made cheap and efficient
        \item Should be possible to start with a small proof of concept (two ALPIDEs, borrowed wall or leftover dark photon materials) and scale up
    \end{itemize}
\end{frame}

%\begin{frame}{Fix vertex fit}
%\begin{columns}
%\column{0.6\textwidth}
%\begin{itemize}
%\item The resolution of the reconstructed mass should be independent of Z but is worse for displaced vertices.
%\item This ad-hoc correction works pretty well: corrM = uncM - 0.15e-3*(elePX/eleP-posPX/posP)*uncVZ/uncM
%\item Hunch: the vertex mass is being calculated using the track directions at $z=0$, or something like that.
%\end{itemize}
%\begin{center}
%\includegraphics[width=\textwidth]{mass_shift_40}
%\end{center}
%\column{0.4\textwidth}
%\includegraphics[width=\textwidth,page=4]{acceptance_40}
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%\includegraphics[width=\textwidth,page=5]{acceptance_40}
%\end{columns}
%\end{frame}

\end{document}
