Resolve "Fix carbon particle charge"

beam-command.asciidoc

@@ -23,14 +23,18 @@ The `label` is optional, it defaults to `UNNAMED_BEAM`.
 [[sec.beam-command.particle-definition]]
 === Particle Definition
 
-The particle mass and charge are defined by:
+The beam particle is defined by `PARTICLE` attribute, which includes a
+direct assignment of the particle mass and charge, as indicated below.
+For other type of particle beams, this attribute must not be used.
+Instead, the particle beam is defined by means of the `MASS` and
+`CHARGE` attributes specified by the user.
 
 PARTICLE:: The name of particles in the machine.
 +
 _OPAL_ knows the mass (see link:format#sec.format.symbolic-constants[Predefined Symbolic Constants])
 and the charge for the following particles:
 +
-POSITRON;;
+  POSITRON;;
     The particles are positrons (`MASS` = latexmath:[m_e],
     `CHARGE` = 1).
   ELECTRON;;
@@ -47,7 +51,7 @@ POSITRON;;
     `CHARGE` = -1).
   CARBON;;
     The particles are carbons (`MASS` = latexmath:[m_c],
-    `CHARGE` = 12).
+    `CHARGE` = 6).
   URANIUM;;
     The particles are of type uranium (`MASS` = latexmath:[m_u],
     `CHARGE` = 35).
@@ -68,7 +72,7 @@ POSITRON;;
     `CHARGE` = 2).
 
 
-For other particle names one may enter:
+For other particle types one may enter:
 
 MASS::
   The particle mass in GeV.