Allowing blended fuel sources

[shimwell]

Currently just 'DD' or 'DT' sources are allowed using the fuel: str = "DT", argument

We could add sources that have a fraction of DT and a different fraction of DD with a more flexible input for fuel.

How about fuel also accepts a list of tuples, where the first entry is 'DD' or 'DT' and the second entry is the relative strength

fuel = [('DD', 0.1, ('DT',0.90)]

or is a dictionary better

fuel = {'DD':0.1, 'DT':0.9}

[RemDelaporteMathurin]

or a proportion of D and T?

fuel = {"D": 0.5, "T":0.5}
fuel = {"D": 0.25, "T": 0.75}

[shimwell]

That would be cool. It would need to have the reaction rate equation built in to find the relative rates of neutron energies

[shimwell]

We could make use of equations in the Bosch and Hale paper https://iopscience.iop.org/article/10.1088/0029-5515/32/4/I07

Or cross section data, which is nicely plotted in this blog post https://scipython.com/blog/nuclear-fusion-cross-sections/