Just as the title says. I’m curious as to how you would go about figuring out the amount of decay products in a given sample of Pitchblende/Uraninite. I would hazard a guess at using the half life formula over and over but something seems off about doing that.

  • $\begingroup$ I don't understand your question. You can analyse a sample and immediately know the composition. Do you want to derive a former composition, e.g. at 10 million or a billion years ago? $\endgroup$ – Karl Apr 14 '18 at 6:50
  • $\begingroup$ He may not immediately know, some decay products will be in trace amounts and some will be very transient. $\endgroup$ – Güray Hatipoğlu Apr 14 '18 at 6:59
  • $\begingroup$ Karl: I trying to figure out what a given sample day 10kg or so of Pitchblende would contain in terms of decay products. I.e. the element composition of Pitchblende as of today assuming it was made when the earth was formed $\endgroup$ – Dalis Apr 14 '18 at 7:27

Well, it is straightforward. You get the amount of radioactive compounds in your mineral. Then find out the decay chain reactions, it generally goes from Uranium to Lead.


example for U-235

Then you will find half-life constants for each reaction and start to calculate from U-235 to lead one by one.

Well if you think that it is just chore, write a Fortran code and enter radioactive decay constants, reactions and make a user input chain part and everyone can calculate the decay products for a given mineral/time.

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  • $\begingroup$ Ah. That was my original method. But wouldn’t that be incorrect? Taking the half life of Uranium-235 over the existence of the Earth or said material would get you the remaining amount of Uranium-235. Then using the difference in masses that would be the Thorium generated. Now doing the half life equation again for thorium makes it sound like it would be like tacting on another existence of Earth or said material. Am I wrong? $\endgroup$ – Dalis Apr 14 '18 at 7:24
  • $\begingroup$ I don't get what is incorrect, and "would be tacting on another existence of Earth or said material". Radioactive decay rate is independent of the amount of material, find the production of Th and removal of Th in a unit time, then multiply it with (start-end)/unit time. Maybe that is more proper. Apply it with all remaining chain. $\endgroup$ – Güray Hatipoğlu Apr 14 '18 at 10:50
  • $\begingroup$ If you found the half life for a kilo of uranium-235. And then when to find the amount of the thorium that has decayed in said time span, wouldn’t that be like repeating the same timespan but for new material? $\endgroup$ – Dalis Apr 14 '18 at 17:44
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    $\begingroup$ Nope, what I said was this. U-> Th -> Pa, let says U halves itself in 1 billion year, Th does it for 500 million. 10 kg U reduces 5 kg in 1 b year, assume nearly 5 kg Th, but in that span Th halves itself twice, and (5kg/2)/2 = 1.25 kg remained. So it is produced 5 kg and decayed 3.75 kg in 1 b, net 1.25 kg generated. Then you will just multiply it with 4.5 to find what left after 4.5 billions year, 5.625 kg Th is the answer. $\endgroup$ – Güray Hatipoğlu Apr 14 '18 at 17:59
  • $\begingroup$ I know good sir. But what I’m saying is when you use the half life equation on thorium, the time used in the equation is it the same time interval as the uranium on or a different one $\endgroup$ – Dalis Apr 14 '18 at 20:12

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