Is promethium costly than radium?
Bru, this may answer your question: Promethium can be formed in nature as a product of spontaneous fission of uranium-238 and alpha decay of europium-151. Only trace amounts can be found in naturally occurring ores: a sample of pitchblende has been found to contain promethium at a concentration of four parts per quintillion by mass. It was calculated that the equilibrium mass of promethium in the earth’s crust is about 560 g due to uranium fission and about 12 g due to the recently observed alpha decay of europium-151. Radium is a decay product of uranium and is therefore found in all uranium-bearing ores. One metric ton of pitchblende yields 0.0001 grams of radium. which is 10 parts per billion. To put this in perspective Promethium concentration is 1 : 4.0 x 10^-18 Radium concentration is 1 : 1.0 x 10^-10 so you may make your conclusion form the fact that Promethium is 25,000,000 times more rare than Radium.
