[Talia94]

Okay so basically, did an experiment using the geiger counter and measured the counts for 234 Thorium which we were meant to be separating from 238 Uranium.

Correcting for background counts, the activity measured was 124 CPM.

I've been given this question..

'What 234 Th activity would you expect to find in a sample of 0.25g of uranyl nitrate (UO2(NO3)2.6H2O)? What mass of 234 Th is this equivalent to?'

Uranyl nitrate is what was used at the start to separate but 0.21g was used.

How do I arrange it so I can work it out for 0.25g? I believe this question may have already been posted but there were no answers to it. This is all the info I've been given, and the aim of the exp is to use the comparison of the measured activity (124 cpm) to the calculated value (?) to determine the yield of separation.

If anyone could shed some light, I'd be very grateful as I have no clue and the teaching staff are still yet to help me..

[Enthalpy]

²³⁸U has a long half-life and its predominant alpha decay makes ²³⁴Th which has a much shorter half-life.

If the Th is supposed to result from U decay and is at equilibrium (as much destroyed as created), you can directly compare both activities.

One refinement is to check the other decay modes of ²³⁸U, and whether your apparatus detects all decay modes of ²³⁴Th.

The other refinement would be to check other possible routes to ²³⁴Th. They're unlikely because it's so near to uranium, the heaviest not very scarce natural element, and I see a simple route from the 238 isotope only.

Though, if your uranium is depleted to be ²³⁸U, it's not a natural sample, so it may contain other nuclides that are much more radioactive like plutonium and more actinides. Then other nuclides may produce ²³⁴Th without going by ²³⁸U.

This is not a remote hypothesis. Depleted uranium is produced from ore and also from recycled reactor fuel, as has been observed at kinetic energy weapons. Then, nuclides in minute quantity provide more activity than the almost stable ²³⁸U: 1ppb of a nuclide with 1yr half-life provides as much as the main nuclide with 1Gyr half-life.