Insulating properties of solder mask?

I am currently working on making a Geiger counter, and the Geiger tube needs a 500v DC power source (currently being produced by a boost converter), and I was wondering how safe it would be to have components over a 500v carrying trace. Are there also any concerns regarding spacing between traces/isolation if there are voltages this high?

There are figures for air gap and voltage around, try Google. I wouldn’t trust the insulation properties of solder mask, use an air gap or a sheet of insulation material.

Leon