After 3 half-lives, only 12.5% (or 1/8) of the original parent material will remain, as the amount is halved three times: 100% -> 50% -> 25% -> 12.5%.
1 : For cobalt-60, which has a half-life of 5.27 years, 50% remains after 5.27 years (one half-life), 25% remains after 10.54 years (two half-lives), 12.5% remains after 15.81 years (three half-lives), and so on.
After one half-life, 50 percent of the radioactive carbon isotope will remain, after two half-lives, 25 percent will remain, and after three half-lives, only 12.5 percent of the parent isotope of radioactive carbon will remain.
**Final Calculation**: Percentage remaining = 100 16 = 6.25 % ### Conclusion: After 4 half-lives, approximately **6.25%** of the original radioactive substance remains.
After three half-lives, only 12.5% of the original parent atoms remain. As more half-lives pass, the number of parent atoms remaining approaches zero.
From the graph, we can see that after two half-lives, the remaining parent material will be 25% of the original amount, and the daughter material will be 75% of the original amount. Therefore, the rock is two half-lives old.
Answer and Explanation: After three half-lives 1/8 (12.5%) of the original sample remains. A half-life is the amount of time it takes for one-half of a sample to undergo radioactive decay.
Answer and Explanation: If a rock contains 25 percent of a parent isotope and 75 percent of its daughter isotope, two half-lives must have passed.
After 7 half-lives, 0.78% of the original substance remains. Sodium-24 has a half-life of 15 hours. How many half-lives will pass in 5 days? 5 days = 120 hours; 120 hours / 15 hours = 8 half-lives.
- Therefore, it takes approximately 3.32 half-lives for the activity of the radioactive sample to decrease by 90%.
What percent of a parent isotopes remains after 2 half-lives? B, After 2 half-lives there will be 25% of the original isotope, and 75% of the decay product.
After four half-life periods, 6.25% of the radioactive substance will be left undecayed.
Two half-lives have passed if a rock contains only 25 percent of its parent isotope and 75 percent of its daughter isotope. This is true because each half-life isotope loses 50 percent of its remaining parent isotope with each cycle.
Only 12.5 percent of the original sample of a radioactive parent isotope will remain after three half-lives have passed.
For a given number of atoms, isotopes with shorter half-lives decay more rapidly, undergoing a greater number of radioactive decays per unit time than do isotopes with longer half-lives.
After three half-lives, the remaining amount of a radioactive substance is (1/2)3 = 1/8 of the original amount. So, if you start with 120 atoms, after three half-lives, you would have 120 x 1/8 = 15 atoms remaining.
After 12.5% of a radioactive sample remains, it indicates that 3 half-lives have passed. This is because after each half-life, the remaining amount is halved: 50%, then 25%, then 12.5%. Therefore, the total number of half-lives is 3.
After one half-life, 50% of a radioactive substance remains. After two half-lives, this amount is halved again, so 50% of the remaining 50% would be left. This is 25% of the original amount.
After the third year (three half-lives), 12.5% of the original radioactive parent atoms remain. After four years (four half-lives), 6.25% of the original radioactive parent atoms remain, and after 5 years (five half-lives), only 3.125% of the original radioactive parent atoms remain.
**Final Calculation**: Now, calculating : 100 32 = 3.125 % ### Conclusion: After 5 half-lives, 3.125% of the radioactive substance remains.
The technique often cannot pinpoint the date of an archeological site better than historic records, but is highly effective for precise dates when calibrated with other dating techniques such as tree-ring dating.
For instance, in the case of strontium-90 whose half-life is 29 days, only 50% of the original amount of isotope would remain after 29 days (1 half-life), only 25% of the original amount would remain after 58 days (2 half-lives), only 12.5% would remain after 87 days (3 half-lives) and so on.
For example, if the given time represents two half-lives, the amount remaining will be 1/2 x 1/2 = 1/4 of the original amount.
After 8 days have passed, half of the atoms of any sample of iodine-131 will have decayed, and the sample will now be 50% iodine-131 and 50% xenon-131. After another 8 days pass (a total of 16 days), the sample will be 25% iodine-131 and 75% xenon-131.