The electrons are a real enigma. We have three types in the model.
What is the relation between inner, quasi-inner and outer electrons?
This is of course the initial question. The model allows the electrons through nuclear reactions to change the type.
What is the structure of the inner electron?
We consider it to be like glue. But can it be considered a particle?
In what way does the quasi-inner electron differ from the inner and the outer electron?
The outer electron or the free electron have more particle like properties.
Why do we see sometimes 2 x 0.511 MeV gamma rays at roughly 180° during β+ decay?
We have an idea why this is the case, but there is still much to figure out.
What is the actual size of the electrons and what does that mean?
This question depends also on the type we are talking about. We might have to distinguish between the actual size and the sphere of influence.
More details on why the β decay spectrum is continuous are required.
This us another topic that needs work.