It has a breathtaking iridescence. An absolutely fabulous piece.
Is it radium? In my opnion, no, not strictly radium.
Radium iridescence is a descriptive term usually applied to pieces made by Millersburg. In fact they coined the term back in 1911. Today the phrase is used to describe an iridescence that is almost mirror shiny. It is very colourful and beautiful, but instead of being matt or satiny, it is almost see-through. (It isn't exactly what Millersburg originally meant by the term, but it is how it has come to be known over the years, by collectors).
So, if it's not radium, what is it? It's not always easy to pigeon-hole an iridescent effect, and frequently different people will have different opinions. The easiest (and least likely to be misunderstood) way to describe it would be to call it very vivid and well iridised. It could even be called "Pumpkin marigold" (a vivid marigold iridescent effect that has lots of purples, reds and deep intense highlights) but I can't be sure from the photo.
Imperial were renowned for quality Carnival Glass.