Table of Contents

- 1 How much of a radioactive sample remains after 4 half-lives?
- 2 How do you calculate half-life decay?
- 3 How much of a 120 g sample of a radioactive isotope will remain after 4 half lives have passed?
- 4 What is the half-life of Iodine 131 if after 24 days 0.125 g remains from a 1.00 g starting sample?
- 5 How long does it take for a radioactive substance to decay?

## How much of a radioactive sample remains after 4 half-lives?

n is the number of half-lives. After 4 hours, only 3.75g of our original 60g sample would remain the radioactive isotope Np-240….Rate of Radioactive Decay.

Element | Americium |
---|---|

Half-life | 25 minutes |

Element | Carbon |

Mass Number (A) | 16 |

Half Life | 740 milliseconds |

**What percent remains after 5 half-lives?**

Thus a first-order chemical reaction is 97% complete after 5 half-lives and 100% complete after 10 half-lives.

**How much of 100g of parent isotope is left after 4 half-lives have passed?**

The half-life of Iodine-131 is approximately 8 days. What is the amount of Iodine-131 left from a 35 gram sample after 32 days? Living matter has a carbon-14 activity of about 16 counts/min per gram of carbon.

### How do you calculate half-life decay?

The time required for half of the original population of radioactive atoms to decay is called the half-life. The relationship between the half-life, T1/2, and the decay constant is given by T1/2 = 0.693/λ.

**How much of a 120 g sample of a radioactive isotope will remain after 4 half-lives have passed?**

After another 30 days ( three half lives or 90 days) 30 /2 = 15 g decays and 15 g remains left. After another 30 days ( four half lives or 120 days) 15 /2 = 7.5 g decays and 7.5 g remains left. after four half lives or 120 days , 7.5 g of the isotope will be left.

**How much of a radioactive sample remains after 2 half-lives?**

After 1 half life , clearly HALF of the original isotope remains. And after TWO half-lives, a HALF + HALF of a HALF , i.e. 34 of the original mass has decayed.

## How much of a 120 g sample of a radioactive isotope will remain after 4 half lives have passed?

**How much of a radioactive sample remains after 2 half lives?**

**How do you calculate radioactive decay?**

Radioactive Decay – Equation – Formula

- Radioactive decay law: N = N.e-λt
- (Number of nuclei) N = N.e-λt
- (Activity) A = A.e-λt
- (Mass) m = m.e-λt

### What is the half-life of Iodine 131 if after 24 days 0.125 g remains from a 1.00 g starting sample?

What is the half life of iodine 131 if after 24 days 0.125g remains from a 1.00g starting sample? you would have to divide 1.00g by 2 to see how many times does it take to get to 0.125g. which equals 3 times then you divide that by 24 to find the half lives which would be 8.

**What is the sample size of a radioactive isotope after 30 days?**

An 8.00 gram sample of a radioisotope decays to a sample of 0.25 grams after 30 days. What is the half-life of the substance? 10. 11. What percent of any given sample of a radioactive isotope remains after 5 half-life periods? SO The half-life of 0-218 is 3 minutes. If you start with a 10 gram sample, how many grams will remain after 9 minutes?

**How many grams of radioactive elements are left after each half-life?**

after one half-life there will be 5 grams of the radioactive element left. After another half-life, there will be 2.5 g of the original element left, after another half-life, 1.25 g will be left. Each and every radioactive element has its own half-life.

## How long does it take for a radioactive substance to decay?

Each and every radioactive element has its own half-life. For instance, 238 U has a half-life of 4.5billion years. A radioactive substance has a half-life of 20 minutes. If we begin with a 500 g sample, how much of the original sample remains after two hours?

**How much of the original sample remains after two hours?**

For instance, 238 U has a half-life of 4.5billion years. A radioactive substance has a half-life of 20 minutes. If we begin with a 500 g sample, how much of the original sample remains after two hours? Two hours is 120 minutes -> six half-lives. At the end of the stated time period, 7.8 g remains.