docs: def decay(self, mass_frac):
  
          """
          this module simply calculate abundances of isotopes after decay.
  
          It requires that before it is used a call is made to
          _read_iso_abund_marco and _stable_species.
  
          Parameters
          ----------
          mass_frac : list
              alist of mass_frac dicts.
  
          See Also
          --------
          _read_iso_abund_marco(), nuutils.Utils._stable_species()
  
          """
  
          import nuutils as u
  
          global decayed_multi_d
          decayed_multi_d=[]
          #print len(mass_frac)
          #print len(decay_raw)
          for iii in range(len(mass_frac)):
              jj=-1
              decayed=[]
              for i in range(len(u.decay_raw)):
                  if u.jdum[i] > 0.5:
                      jj=jj+1
                      dummy=0.
                      for j in range(len(u.decay_raw[i])):
                          try:
                              dum_str = u.decay_raw[i][j]
                              dummy = dummy + float(self.mass_frac[iii][u.cl[dum_str.lower().capitalize()]])
                              #print cl[dum_str.lower().capitalize()]
                              #print dum_str, mass_frac[iii][cl[dum_str.capitalize()]]
                          except KeyError:
                              None
                              #print 'I am not in the network:',decay_raw[i][j]
                          except IndexError:
                              None
                              #print 'I am not read',cl[decay_raw[i][j].lower().capitalize()],decay_raw[i][j]
                      decayed.append(dummy)
              decayed_multi_d.append(decayed)