Merge pull request pyne#724 from rachelslaybaugh/develop

tutorial updates again

Author: Rachel Slaybaugh

tutorial/04-reaction_names.ipynb

@@ -45,7 +45,7 @@
       "produced, then the number precedes the particle type.  Thus, one\n",
       "neutron and two protons are given by \"n2p\".  However if this would\n",
       "result in the name starting with a number, then the name is\n",
-      "prepended with ``z_`` to indicate any incident particle.  For\n",
+      "prepended with ``z_`` to indicate a number of incident particles is coming.  For\n",
       "example, a reaction yielding two neutrons is \"z_2n\" (because\n",
       "\"2n\" is not a valid variable name in most programming languages).\n",
       "\n",
@@ -373,4 +373,4 @@
    "metadata": {}
   }
  ]
-}
+}