Not sure what you mean by "had-lives". After 3 half lives, approx 1/8 would remain.
After the first half-life, you will have one half of the starting amount. After a second half-life period, you'll be down to one quarter. Of the part that radioactively decays, about 11% of it will decay to 40Ar, and the remainder to 40Ca. Of your total sample of ordinary potassium, only 0.012% will be 40K. The half-life of 40K is about 1.3x109 years.
It will take twice the half-life of the radioactive material for it to decay through two half-lives. If the half-life is 1 hour, it will take 2 hours for the material to decay through 2 half-lives.
After 50 years, 1500 g of actinium-227 will have undergone approximately 2.3 half-lives (50 years / 21.772 years per half-life). This means that approximately 25% (50% decayed after 1 half-life, and 50% of the remaining amount decays after the second half-life) of the original sample will remain radioactive, so there will be around 375 g of actinium-227 remaining.
The half-life of the isotope is 16.5 hours, so it takes 16.5 hours for half of the sample to decay. To find the time it takes for three fourths of the sample to decay, you would calculate 2 half-lives (2 x 16.5 hours) as three fourths is equal to 1.5 times the original amount (1 + 0.5). Therefore, it would take 33 hours for three fourths of the sample to decay.
Oxygen, under normal conditions, is non-radioactive. But there are traces of radioactive isotopes present which makes the oxygen slightly radioactive. Additionally, these isotopes have long half-lives, so the radiation given off will not be a lot within a period of time.
1/8 of the original amount remains.
After 5 half-lives, 3.125% (or 1/2^5) of a radioactive sample remains. Each half-life reduces the sample by half, so after 5 half-lives, there is only a small fraction of the original sample remaining.
After three half-lives, only 1/8 (or 12.5%) of the original radioactive sample remains. This is because each half-life reduces the amount of radioactive material by half, so after three half-lives, you would have (1/2) * (1/2) * (1/2) = 1/8 of the original sample remaining.
An eighth remains.
Not sure what you mean by "had-lives". After 3 half lives, approx 1/8 would remain.
If I take a radioactive sample of 400 moles of an unknown substance and let it decay to the point of three half-lives I would have 50 moles left of the sample. 1/2 of what is left will decay in the next half-life. At the end of that half-life I will have 25 moles left of the unknown substance or 4/25.
Approx 1/8 will remain.
After 2 half lives, 25% of the original radioactive sample remains unchanged. This is because half of the sample decays in each half life, so after 1 half life, 50% has decayed, and after 2 half lives, another 50% has decayed, leaving 25% unchanged.
Half of the original sample of a radio isotope remains after a half-life period. After two half-life periods, one-fourth of the radio isotope remains.
Three half lives have elapsed. This can be determined by calculating how many times the original sample size must be halved to get to one eighth: (1/2) * (1/2) * (1/2) = 1/8.
Half life of an element can't be changed.. It is a characteristic of a radioactive element which is independent of chemical and physical conditions.. Half life is that time in which half of radioactive sample( i.e., a radioactive element) decomposes. So no matter what amount you take half life of an element remains same.
Nitrogen-16 has a half-life of about 7.13 seconds. After 36.0 seconds, there would be 3 half-lives. Therefore, 1/2 * 1/2 * 1/2 = 1/8 of the original sample remains unchanged.