ΔE 18.9, loose: different enough that you should pick on purpose. Radium is noticeably lighter, cooler than Thallax Gold.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Radium is noticeably lighter, cooler than Thallax Gold.
The same difference applies the other way round: Thallax Gold is noticeably darker, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Thallax Gold on the colour wheel See Radium on the colour wheel
All matches: Thallax Gold equivalents · Radium equivalents