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21cm.tex
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21cm.tex
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\documentclass{standalone}
%\pagenumbering{gobble}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% HI 21cm line schematic
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{tikz,xcolor}
\usetikzlibrary{arrows,snakes}
\begin{document}
\tikzset{
level/.style={thick},
trans/.style={thick, dashed,->,shorten >=2pt,shorten <=2pt,>=stealth},
photon/.style={thick, ->, snake=snake, line after snake=1mm}
}
\begin{tikzpicture}[scale=1.0, font=\sffamily]
% Draw the energy levels
\draw[level] (1.3cm,0cm) -- (5.5cm,0cm);
\draw[level] (1.3cm,3cm) -- (5.5cm,3cm);
\node[right] at (3.8,3.25) {\small{$n_2/n_1=3$}};
% Draw scale bar on left side
\draw[thick, ->] (1.0,0.0) -- (1.0,3.5);
\draw[level] (0.9,0.0) -- (1.1,0.0) node[left] {\small{$E=0$~~~}};
\draw[level] (0.9,3.0) -- (1.1,3.0) node[left] {\small{$6\,\mu$eV~~~}};
% Draw the transition
\draw[trans] (1.9cm,3cm) -- (1.9cm,0cm);
% Draw the photons
\draw[photon] (1.9cm,1.5cm) -- (5.0cm,1.5cm);
\node[right] at (2.1,1.9) {\small{21 cm, 1.42 GHz}};
%\node[right] at (2.1,1.1) {\small{$A_{21} = 2.9\times 10^{-15}\,s^{-1}$}};
%\node[right] at (2.1,1.1) {\small{$A_{21}$ = 1/11 Myr}};
\node[right] at (2.1,1.1) {\small{$1/A_{21} \sim 11$ Myr}};
% Draw the proton-electron spins
\draw[thick] (5.75,3) circle (0.15cm);
\draw[thick] (6.10,3) circle (0.15cm);
\draw[thick, ->] (5.75,2.7) -- (5.75,3.3);
\draw[thick, ->] (6.10,2.7) -- (6.10,3.3);
\draw[thick] (5.75,0) circle (0.15cm);
\draw[thick] (6.10,0) circle (0.15cm);
\draw[thick, ->] (5.75,-0.3) -- (5.75,0.3);
\draw[thick, ->] (6.10,0.3) -- (6.10,-0.3);
\end{tikzpicture}
\end{document}