I think the nuclear tab is insufficient. Here are some suggestions:
Seiverts (Sv on HUD)-Measures radiation, for the HUD. The more seiverts, the more faded the element's colors get. Too many seiverts can kill STKM and FIGH. Can protect things from Sv with INSL. 5 Sv gives STKM/STK2 cancer, which slowly drains the STKM's health. 10 Sv can kill a stickman in about 5 minutes ingame.
If at least 500 Sv can kill a STKM instantly.
ISOZ, ISZS, URAN, PLUT, GRPT, RADN all produce Sv.
GRPT-Graphite, powder, produces heat and pressure when exposed to NEUT, used in nuclear reactors like Chernobyl. Slowly decays and contaminates whatever it touches with seivels.
RADN-Radon gas, infects RADI.
RADI-Radioactive waves, energy, contaminates other elements with seiverts.
GRGC-Geiger counter, produces SPRK in various intervals when infected with seivels. I.E, if insanely high seivels, produces a constant tone of SPRK. If very low, about one spark each second. If at a fatal dose (for stickmen), it should turn red.
BNAN-Banana, very, very low seiverts when spawned. Just for lols.
RADW-Radioactive water. Produced by steam infected with high amounts of Sv.
RDSN-Radioactive snow. Water frozen, exposed to pressure, and infected with Sv.
SPECIAL tab:
HAZM-Hazmat suit, turns STKM/STK2 yellow and protects from super-high doses of Sv.
GASM-Gas mask, makes STKM/STK2's face gray and protects it from gasses infected with Sv and VRSG.
That's all I got. I plan for this to be a mod.
This is a really cool mod sugestion. Where it will find it's place in Vanilla TPT, I don't know... these elements seem too gimicky, as you said yourself
However, if this were to be implimented into a mod, tweaking the stickmen will benifit you, as their current state is glitchy and unpredictable.