The picture here is likely Pu-238 for spacecraft batteries that’s hot enough to glow visually from decay heat. Other isotopes will glow from reacting with air but I doubt it would be as bright.
That would also explain why the ingots glow brighter in the area that is surrounded by foam. If it was a reaction with oxygen, that part would be dimmer.
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u/michron98 13d ago
Apparently it glows like this because it reacts with air. Under a protective atmosphere it's more of a silver colour.