What is the half life of Uranium 234?
This is the information that I found on the internet:
Half-Life of Uranium (234)
Chamberlain, Owen; Williams, Dudley; Yuster, Philip
Physical Review, vol. 70, Issue 9-10, pp. 580-582
"The half-life of U234 has been determined by two independent methods. The first method involves a re-measurement of the relative isotopic abundance of U234 and U238 in normal uranium; from this measurement the half-life of U234 can be obtained in terms of the known half-life of U238. The value obtained by this method is 2.29+/-0.14×105 years. The second method involves the determination of the specific α-activity of U234 from the total specific α-activity and relative isotopic abundances of several enriched uranium samples. The value obtained by this method is 2.35+/-0.14×105 years. Both values for the half-life are somewhat smaller than the currently accepted value of 2.69+/-0.27×105 years.
This works out to be about 245,250 years give or take 490 years.
Remember that half life is a measure of how long it takes for half of the radioactive sample to decay into a non-radioactive substance. This is NOT constant. Within the first few years most of the substance might already be decayed and then it may take the next thousands of years to decay the other portion of the substance.