An isotype 234/92U is 245,000 years.?

Question

An isotype 234/92U is 245,000 years. What percentage of the original material will be left after 980,000 years?

I need a full calculation in a help to undertand the question and answer. Thank you.

Answer 1

The half life of the isotope is 2,45000 years.

9,80,000 / 2,45000 = 4

So, the amount will be 1/2 X 1/2 X 1/2 X 1/2 = 1/16 th of the original. In percentage terms, that will be 100 / 16 = 6.25%

Answer 2

This isotope of Uranium is said to have a half-life of 245,000 years. That means that every 245,000 years, you have 1/2 left of what you started with. 980,000 years is 4 half-lifes, so you would have left 1/16 of the original mass. The other 15/16 would have been converted to Thorium or whatever.

Answer 3

Number of half-lives(n)= 980000/245000 = 4

After 1 half life ---- 1/2 of the material is left behind
After 2 half lives ----- 1/2 * 1/2 = 1/4 of the material is left behind
After n half-lives --- (1/2)^n of the original material is left behind

n=4
(1/2)^4 = 1/16th of the material will be left behind.

Answer 4

980000 / 245000 = 4, so 4 half-lives have passed.

So you now have-:

1 / 2^4 = 0.0625 or 6.25%