The half-life of a radioactive nuclide when 95% of it is left after one year is 13.5 years.
AT = A0 2(-T/H)
0.95 = (1) 2(-1/H)
ln2(0.95) = -1/H
H = -1/ln2(0.95)
H = 13.5
The half-life of a radioactive substance is the time that it takes for half of the atoms to decay. With a half-life of 10 days, half has decayed in this time. After 20 days, a further 10 days/another half life, a further half of the remainder has decayed, so 1/4 of the original material remains, 1/4 of 15g is 3.75 grams. This is the amount of original radioactive substance remaining, but it’s daughter isotope ( what the decay has produced ) is also present, so the original sample mass is effectively constant, especially in a sealed container. Even in an unsealed container, and assuming alpha ( helium nucleii) emission, a drop in mass per radioactive atom of 4 Atomic Mass units, compared with the original atom of, say 200 amu is only 2% mass decrease, less for heavier decaying nucleii.
Yes. There are isotopes of elements that are simply not found anywhere in the universe (and even if they did exist momentarily, their lifetime is so short that in the next moment they would have decayed into a different more stable isotope).
Here is a picture of some tooth decay: http://www.icfcd.com/decayed-teeth.html
Since half of the atoms of the original substance will have decayed after 5 hours, half of what is left will have decayed after the next five hours. The answer is 0.25 or one fourth of the original atoms will remain.
I would consider it safe after 5 half-lives. by 5 it has decayed to 3% of original level, by 10 it has decayed to 0.1% of original level.
That's called a daughter isotope, or a daughter product. (The original isotope that decayed is the parent isotope.)
The total amount of radioactive substance will never reach zero because it decays in half-lives. For C-14 is 5730 years, this means that after 5730 years one half of the original material will have decayed. After another 5730 years the remaining radioactive material (1/2 the original) will have decayed by 1/2 once again. -An infinite crowd of mathematicians enters a bar. The first one orders a pint, the second one a half pint, the third one a quarter pint... "I understand", says the bartender - and pours two pints.
The half-life of a radioactive substance is the time that it takes for half of the atoms to decay. With a half-life of 10 days, half has decayed in this time. After 20 days, a further 10 days/another half life, a further half of the remainder has decayed, so 1/4 of the original material remains, 1/4 of 15g is 3.75 grams. This is the amount of original radioactive substance remaining, but it’s daughter isotope ( what the decay has produced ) is also present, so the original sample mass is effectively constant, especially in a sealed container. Even in an unsealed container, and assuming alpha ( helium nucleii) emission, a drop in mass per radioactive atom of 4 Atomic Mass units, compared with the original atom of, say 200 amu is only 2% mass decrease, less for heavier decaying nucleii.
The basic idea is to measure the amount of the radioactive isotope, and of one or more of its decay products. The older the rock, the larger the percentage of the original isotope that decayed - so the ratio between the original isotope and the decay product changes over time.
Being radioactive neptunium is decayed down to a stable isotope.
Half life refers to the time required for the change (decay) of a radioactive nucleus to a lighter, possibly more stable, nucleus.Starting with 5,000 radioactive atoms, at the end of first year, half would have decayed leaving 2,500. Following the same pattern, the end of the second year would see only 1,250. By the end of year 5, there would be just 156 radioactive atoms.
Using the formula Nt = N0*(1/2)t/t1/2 where Nt is the amount of stuff remaining after an amount of time, t, and t1/2 is the half-life, you get Nt = .036N0. So about 3.6% of the radioactive stuff is left.
radon-222
Similarity: Both show that the radioactive atoms decrease and decayed atoms increase Difference: an actual decay is longer.
The partly decayed substance is vegetation bogs.