what is the half life of an isotope that decays to 125
Radioactivity
With the wrong number of neutrons, nuclei tin fall apart. A nucleus volition regain stability past emitting blastoff or beta particles and then 'cool down' by emitting gamma radiations.
Half life
Radioactive decay is a random procedure. A cake of radioactive material will incorporate many trillions of nuclei and not all nuclei are likely to disuse at the same time so it is impossible to tell when a particular nucleus will decay.
Information technology is not possible to say which item nucleus will decay next, but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. Scientists cannot tell when a particular nucleus will disuse, but they can utilize statistical methods to tell when half the unstable nuclei in a sample will have decayed. This is called the half-life .
The illustration below shows how a radioactive sample is decaying over time.
From the start of timing it takes 2 days for the count to halve from 80 downward to xl. It takes some other ii days for the count rate to halve again, this time from 40 to 20.
Note that this 2d ii days does not see the count drop to null, merely that information technology halves once more. A third, ii-day period from four days to six days sees the count rate halving once again from 20 downwardly to 10.
This process continues and although the count charge per unit might become very minor, it does non drop to zip completely.
The one-half-life of radioactive carbon-14 is 5,730 years. If a sample of a tree (for instance) contains 64 grams (g) of radioactive carbon after 5,730 years it will contain 32 g, later on another v,730 years that will have halved once more to 16 g.
Calculating the isotope remaining - College
It should too be possible to state how much of a sample remains or what the activeness or count should get afterwards a given length of time. This could be stated equally a fraction, decimal or ratio.
For example the amount of a sample remaining after four half-lives could be expressed as:
- a fraction - a ½ of a ½ of a ½ of a ½ remains, which is ½ × ½ × ½ × ½ = 1/16 of the original sample
- a decimal - 1/xvi = 0.0625 of the original sample
- a ratio - given in the course 'activity later on north half-lives : initial action' , in this case 1:sixteen
This could so be incorporated into other information. So if the half-life is ii days, four half-lives is 8 days. And so suppose a sample has a count charge per unit of three,200 Becquerel (Bq) at the starting time, what its count rate would be later on 8 days would be ane/16th of three,200 Bq = 200 Bq.
Example
The half-life of cobalt-sixty is v years. If there are 100 k of cobalt-60 in a sample, how much will exist left after fifteen years?
15 years is three one-half-lives then the fraction remaining will be \((\frac{1}{2})^three = \frac{ane}{8} = 12.5g\)
As a ratio of what was nowadays originally compared to what was left, this would be 100:12.v or 1:0.125
- Question
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What is the half-life of a sample where the action drops from 1,200 Bq down to 300 Bq in 10 days?
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Half of one,200 is 600, half of 600 is 300. And so it takes two one-half-lives to drib from 1,200 Bq to 300 Bq, which is ten days. So one one-half-life is five days.
Source: https://www.bbc.co.uk/bitesize/guides/z3tb8mn/revision/3
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