Add decay energy dataset

[tristan-gardner]

Description

In response to the changes requested on this feature branch, this PR adds a data set which includes the decay energy info for each nuclide.

• Adds the source file (.RAD)
• Updates the notebook to have the code used to process and write it to csv
• Switches DF.append() calls out for DF.concat() - append is now deprecated
• Adds the final csv file

Source info

Here is the format of the source data - along with a key that describes the radiation type

Here is what a few lines of abbreviated data looks like from the .RAD file

Ac-223 2.10m 480
2 8.38497E+00 6.06280E-05 X
2 2.14756E-05 1.04461E-04 X
... (478 more rows)
Ac-224 2.78h 682
2 1.26364E+00 6.05941E-05 X
2 1.52234E+01 7.12229E-05 X
... (680 more rows)

Some open questions

The radiation data seems to cover a lot of different types, but there are some notable exceptions e.g. EC an IT, are these included in other columns? Where can we find this info if not?

How exactly should yield and energy be understood together - my best guess was to do a weighted average of them per decay type, so for a given isotope, take all entries with the same decay type and add up the energies multiples by the yields.
Is this right?

If ^ is not the right way to calculate energy per decay? What is? How do we get down to one value per each decay type?

[alexmalins]

Thanks for this @tristan-gardner - see comment here for my proposal on the way forward

And thanks for catches on the now deprecated pandas APIs!