Ionisation due to Radioactive Decay

To activate ionization of H2 and He due to radioactive decay of radioactive elements you need to add two reactions to Reaction.in e.g.

  229 He      RDP             He+     ELECTR                  0.85E+00  0.00       0.0000    Umebayashi2009
  230 H2      RDP             H2+     ELECTR                  1.00E+00  0.00       0.0000    Umebayashi2009

To activate this reactions the radioactive decay ionization rate for H2 ''RDI' has to be set in Parameter.in

7.3E-19     ! RDI         [1/s]    : radioactive decay ionization rate for H2

the default is zero (no ionization)!.

The implementation is based on Umebayashi & Nakano (2009 [http://iopscience.iop.org/0004-637X/690/1/69/]). The value 7.3E-19 is taken from Table 2 of the Paper and corresponds to the ionization rate of 26Al. It is assumed that 26Al is the dominant radioactive decay species for the ionization.

However this implementation is very simplistic and assumes a constant ionization rate throughout the disk. Which is not true for two reasons. In the upper layers the protons and electrons released by the radioactive decay can escape the disk without interaction with the medium. But in this region usually X-Ray/UV and/or CR ionization is dominant and the contribution due to radioactive decay is negligible.
In Umebayashi & Nakano (2013 http://iopscience.iop.org/0004-637X/764/1/104/) the influence of dust settling/growth on the RDI is discussed. The RDI is than not longer constant throughout the disk (higher in the midplane and lower in the upper regions of the disk). However this effect is at the moment not considered.
Generally spoken the RDI is only important in regions where the CR and X-Rays are absorbed (which is usually only the case in the midplane of the inner region of the disk) otherwise the CR and X-Ray ionization is dominant. So the radioactive decay ionization is only important if one wants to study the ionization fraction of the disc in the midplane (e.g. MRI). For the fitting of an object it should not have any impact.

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