13.5 billion years
Depending on the isotope: - for 235U: 7,038.108 years - for 238U: 4,468.109 years etc.
Approx. 9 billion years.
It would take one half-life for the 10 g of uranium to decay into 5 g. The half-life of uranium is around 4.5 billion years, so it would take approximately 4.5 billion years.
Three and a half years.
Uranium has 29 natural and artificial isotopes. Each isotope has his specific half life; for the natural isotopes the half lifes are: U 234: approx. 2.45 x 105 years U 235: approx. 7.04 x 108 years U 238: approx. 4.46 x 109 years
Three and a half years.
1 ounce and three large testes
Three and a half years
[(7,038 ± 0,005) .108 years] x 3
The half-life of 214Bi is 19.7 minutes. However, it has two decay modes, neither of which leads directly to lead; that complicates things. One of the decay modes leads to 214Po, which then quickly (half-life 0.0016 seconds) decays to 210Pb. The other one leads to 210Tl, which has a half-life of 1.3 minutes and also decays to 210Pb. So: Half of the 214Bi will be gone in 19.7 minutes; a bit after that half the sample will be 210Pb.
42 months
After 4.47 billion years, roughly half of the original atoms of uranium-238 would have decayed to lead-206 through alpha decay. This means there would be about 30 atoms of uranium-238 remaining.