Fixed typo in Exercises_HCAL.tex

exercises/Exercises_HCAL.tex

@@ -17,7 +17,7 @@
     \end{equation} 
         while as a reminder the radiation length is defined as
         \begin{equation}
-            X_0 = \mathrm{const.} \, \frac{A}{N_A \sigma_{\mathrm{pair}}} \, \propto \, A / Z^2 \ quad .
+            X_0 = \mathrm{const.} \, \frac{A}{N_A \sigma_{\mathrm{pair}}} \, \propto \, A / Z^2.
         \end{equation}
         Plot both nuclear interaction length and radiation length for as a function of A and Z. Put markers for materials in our material list for simulation.
     \item Adapt your EM calorimeter to also capture Hadronic showers.