Q&A for How to Calculate Half Life

One quick way to do this would be to figure out how many half-lives we have in the time given. 6 days/2 days = 3 half lives 100/2 = 50 (1 half life) 50/2 = 25 (2 half lives) 25/2 = 12.5 (3 half lives) So 12.5g of the isotope would remain after 6 days.

We would need to know how much material you start with in order to solve this problem.

Since the whole is 100%, the first half-life would drop to 50% and then to 25%. Because it takes the isotope 26.7 hours to reach 25%, and there are only 2 halves from 100 to 25%, divide 26.7/2, and you'll get 13.35 hours as the half life.

Here, 100g becomes 50g, which is exactly half. It took three months to do this. Three months is its half life.

Half life simply means a radioactive element's active weight will remain half after that particular time. In this case, two minutes 32 seconds means 152 seconds is eight times of the half life of carbon-10, so it will undergo eight half lives in this time.

After first half-life: 600/2=300; After second half-life: 300/2=150; After third half-life: 150/2=75 nuclei.

Make up an initial amount, then see how long it takes for there to be 4% of the initial amount remaining. For example, you could start with 100 as the initial amount and then see how long it takes for 4% of 100, which is 4, to remain.

It is 28.8 years.

Decay constant of any element is equal to the fraction of decaying atoms per unit time.

In 1 hr = 60 minutes, 60 minutes / 30 minutes = 2 half-lives would have passed. So, remaining amount after an hour will be 20 grams x (1/2)^2 = 20 x (1/4) = 5 grams.

There is insufficient data in this problem. You need to provide the amount remaining after 12 hours to solve this.

The first half life is 160/2=80, the second half life is 80/2=40, and so on up to 6 half lives, which equals 2.5 grams.

6 months, if half = 4 then the whole life = 8 and 3 months is 3/4 of half the life so 6 months = 3/4 of the whole life. 3/4=6/8.

This will take some equation re-arrangement but if you take the half-life equation: t 1/2 = t / (log (.5)(N(t)/No)), then we can rearrange this to: log(.5)(N(t)/No) = t / t 1/2, which would look like this if you take the sample to be 100kg or 100%: log(.5)(N/100) = 6400 / 1600. So, after even more solving and re-arranging, it would look like this: N / 100 = 4 / log(.5), which would finally give us: N / 100 ~ -13.287........ N = 100(-13.29) ~ -1329. Now, the answer is a percentage decrease of mass, so that is why it is negative. When you plug it back into the equation, make sure that it is positive.

Well the simplest thing would be to use a stopwatch, however I don't think that they will last years. So I suggest that you record the time at which you want to start 10 am, 3:45 pm, and then after a few years at the time time you started just count how many days have passed and there you go. Started at 12:30 am, July 1st, 2019, second record at 12:30 am, July 1st, 2030. 2030-2019 = 11 yr and I hope you measured the mass after all this time, otherwise it's back to square one.

The sample is never going to completely decay because you can take the half of every number, as small as it gets, and it'll get smaller but never reach 0. So, technically you will never no when it completely decays. It could, however, possibly be destroyed or reduced through massively high incineration: do some research online to learn more.

2 mg has reduced to 0.25 mg, which will happen in three half lives, or 36 hours. 2 mg reduces to 1 mg after 12 hours, 0.5 mg after 24 hours, and 0.25 mg after 36 hours.

You need to figure out how many half lives past. 9600/1602 gives you that number. Then you can figure out the percent 100. (1 half live is 50%, 2 half lives is 25%...etc.) that’s the percentage left. Then its just figuring out the rest of the 100. So if 500 grams is = to 25% then it’s 1/4 of 100 so 500g * 4= 2000 grams.

No. It is an exponential function, so at the end of the first half-life, half is left, and at the end of another year, half of that will be left, or 25%, at the end of the third year (3 half-lives) it will be 12.5%, and so on.

As Ra-226 has a half life of 1600 years, after 6400 years, 4 half lives have passed. So, the percentage left will be 6.25%. For example, if you have 1 kg of Ra-226 at first, then after 6400 years or 4 half lives of Ra-226, the quantity of Ra-226 you have left is 62.5 grams.

As the half life of an element is 90 days, after 135 days, 1 1/2 half lives have passed. So, the percentage of reduction in mass at the end of the 135-day period is 50% because 1 half life have passed, and 12.5%, as the second half life is only half passed. So, the percentage of reduction in mass at the end of the 135-day period is 62.5%

If after 100 days, 75% of the parent nuclei are disintegrated, then using some math, we can calculate that 2 half lives has passed. So, the half life of that atom if 50 days.