I How to determine the energy of photons released in decay

There is no "equation". While it is possible to get some estimates via nuclear models, the most precise results are usually from experiments, and you can check the published material.

Note that tritium has a very low-energetic beta decay, the emission of photons is rare and those cannot have a high energy.
Pu-237 mainly decays via electron capture, you can calculate the maximal photon energy via energy conservation, but the emission of an electron is also a common result, which can but does not have to be accompanied by the emission of photons.

 

No.

 

You have a different thread about it, please continue there.

You clearly do not have the required knowledge to work with potentially radioactive material safely anyway.