Some observations on abundance:

The data for this is in spreadsheet Fe56-58.xls which can be downloaded from

https://drive.google.com/file/d/0B3pdkE0Liyu2SFJlYVpWclFueVk/edit?usp=sharing [nofollow]From this the nuclear density curves can be drawn for the decay chains leading to the stable Isotopes.

As can be seen the diagram for 56Fe is considerably more complex than those for 57 and 58. This complexity is mainly due to the multiple decay modes of some Isotopes.

The data tables therefore also show the relative probabilities of the daughter Isotopes.

It is clear from the data that the most probable decay mode also has the highest decay energy. This allows a reasonable estimate of the proportions even where a probability is not given in the source data.

From the raw data, 56Fe has seven source isotopes; 57Fe has six source isotopes; and 58Fe has just four. But this simple view can be misleading.

In 56 Fe the chain from 61AS has only a 0.023% probability in the decay from 60Ge to 56Ni. Similarly the decay from 57Ti is only 0.3% and from 57V only 0.4%.

In the 57 chains only 58Sc has a full yield to 57Fe. The decay of 59Sc gives only 30% leading to 57Fe; similarly 58Ga allows 35% from 57Zn; 60As 35% also from 57Zn; and 59Ga only 3% at 58Zn.

The remaining chain 57Ca is shared with 56Fe which takes 30% of the initial decay and another 33% at 57Sc.

The net yield to 57Fe is 66% of 70% or only 46.2%

For 58Fe the chain from 59Sc is 70% in favour, but at 59V less than 1% continues to become 58Fe.

The chain from 59Ga (and 59Zn) effectively terminates at the extremely long lived 2 beta decay 58Ni. Leaving just the chain from 58Sc, and the OP2 58Co.