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Questions tagged [half-life]

Half-life is the time required for an attenuating quantity to reduce to half of its initial value. It is proportional to the mean lifetime, whose inverse is the decay constant. It is a constant for exponential decay.

Half-life is the time required for an attenuating quantity to reduce to half of its initial value. It is proportional to the mean lifetime, whose inverse is the decay constant. It is a constant for exponential decay.

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How do we know that radioactive decay rates are constant over billions of years?

A friend and I recently discussed the idea that radioactive decay rates are constant over geological times, something upon which dating methods are based. A large number of experiments seem to have shown that decay rate is largely uninfluenced by…
Pertinax
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Why is a neutron in free state unstable?

A neutron is a neutral particle which is merely some times more massive than an electron. What makes it so unstable outside the nucleus that it has a half life only of about 12 min?
kalyani
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Can 1 kilogram of radioactive material with half life of 5 years just decay in the next minute?

I wondered this since my teacher told us about half life of radioactive materials back in school. It seems intuitive to me to think this way, but I wonder if there's a deeper explanation which proves me wrong. When many atoms are involved, half life…
uylmz
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Why does the same proportion of a radioactive substance decay per time period? (half life)

Just wondering, if decay is random, why does the activity half every half life, as in, why does it have to reduce by the same proportion in the same time period?
Saharsh Aanand
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Can radioactivity be slowed through time dilation?

Can radioactivity be slowed using the effect of time dilation? If you put cesium, tritium or uranium in a cyclotron at relativisitic speeds, do their half lives become longer in our frame? Could this be used as a means to store radioactive material?
Michael
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Why is radioactive half-life constant?

Say you have just four radioactive atoms with a half-life of one hour. (I am using a small number of atoms to keep it simple and illustrate my confusion more clearly). So that means one hour from now, two of the atoms will have decayed (on average)…
Luke B
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Why is the (free) neutron lifetime so long?

A neutron outside the nucleus lives for about 15 minutes and decays mainly through weak decays (beta decay). Many other weakly decaying particles decay with lifetimes between $10^{-10}$ and $10^{-12}$ seconds, which is consistent with $\alpha_W…
Forever_a_Newcomer
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Does the halflife time of a radioactive material decrease if its temperature increases?

If at high temperatures atoms are more intensely interacting with each other or emitted photons that also could make the core vibrate. Is in these circumstances the radioactive material more likely to fission faster? Can this be used to get rid of…
Krešimir Bradvica
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Why do nuclei decay so fast and slow?

Why do nuclei like Oganesson (also known as Ununoctium, this is the 118th element on the periodic table) decay in about 5 milliseconds? This is weird that they decay. In comparison, why do elements like uranium take about 200,000 years to decay, or…
science error
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How does a half-life work?

Carbon-14 has a half-life of 5,730 years. That means that after 5,730 years, half of that sample decays. After another 5,730 years, a quarter of the original sample decays (and the cycle goes on and on, and one could use virtually any radioactive…
user37390
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Does average lifetime even mean anything?

So today I was trying to derive an expression for the number of radioactive atoms remaining after a time $t$ if I began with $N_0$ atoms in total. At first I tried to assume that they had an average lifetime and work from there, but my friend…
QCD_IS_GOOD
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How do we know that some radioactive materials have a half life of millions or even billions of years?

If a radioactive material takes a very long time to decay, how is its half life measured or calculated? Do we have to actually observe the radioactive material for a very long time to extrapolate its half life?
davitenio
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Why is carbon dating limit only 40,000 years?

For an example, when they tried to get the carbon dating for presence of Aboriginal people in Australia they get to the number 40,000. But it could be much earlier. Why is that 40,000 years limit for carbon dating methods?
Derfder
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Why is there a sudden drop-off in half-life of isotopes at around 130 neutrons? Is there a name for this?

Pertaining to the chart of nuclides, there is a region above Bismuth, in which the relatively continuous trend of stability is interrupted by a batch of isotopes all with extremely short half-lives. I know that "magic numbers" contribute to the…
Xiphosura
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Why is this way of calculating mean life of radioactive atoms incorrect?

Suppose there are $N$ radioactive atoms and the half life of decay is $t$. Then after one half life the number of remaining atoms will be $\frac{N}{2}$. And so after each half life the number will be halved. Which means, $1/2$ of the atoms will have…
Theoretical
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