Question

Question #63c46

Answer 1

A nuclide's half-life expresses the time needed for half of the atoms in the respective sample to undergo radioactive decay.

Since your U-235 has a half-life of 703 million years, this is exatcly how much time must pass before half of the sample undergoes decay.

So, to answer your question, it will take 703 million years for the sample to reach half of its original size. It will take another 703 million years for the sample to reach 1/4 of its original size, another 703 million years before it reaches 1/8 of the original size, and so on...