Half Life Explained

[lnm]

I know that half life is the time period for half the radioactive nuclei to decay. That if the half life of carbon 13 is 1000years... in a thousand years you'll have half the amount of carbon 13 as you did when you started.

 

These are the sorts of explanations I can find but I would like to know what is actually happening. If I have one carbon 13 atom, do I end up with half the atom? Does it eventually disappear? What exactly is "radioactive decay"?

[Double K]

What exactly is "radioactive decay"?

 

The measure of energy dissipation?

 

You don't end up with half an atom, but it now carries half of its energy

and transforms the element

eg carbon14 becomes nitrogen14

[Mr Skeptic]

Each atom decays completely or not at all. For carbon 14, there's about 4 = 4.3 × 10^22 atoms in a gram. Or if you prefer, 43,000,000,000,000,000,000,000 atoms in a gram. Half of them will decay, half will not. Eventually, you will end up with no atoms at all, or perhaps there might still be an atom when you'd "expect" to find half an atom.

[ewmon]

We can look at radioactive decay in more than one way. We can look at numbers of isotopes that decay over a certain amount of time, or we can look at the probability of a single isotope decaying.

 

It's like flipping 10,000 coins, and realizing that you'll end up with about 5,000 heads and 5,000 tails. Or, you can look at only one coin and realize that, when you flip the coin, there''s a 50% probability it'll be heads and a 50% probability it'll be tails.

 

Same thing for isotopes. Over the course of 5,730±40 years, there's a 50% probability that a Carbon-14 isotope will decay to Nitrogen-14, and a 50% probability that it won't. When you look at large populations over this time span, half of them will decay and half of them won't. This decay has a non-linear relationship with time, which is called an "exponential decay".

 

Personally, I'm disappointed with this question, as I assumed from the title that it was about the Half-Life computer game.

[vordhosbn]

Personally, I'm disappointed with this question, as I assumed from the title that it was about the Half-Life computer game.

 

+1

I also thought that this thread will be concerned with inter-dimensional scientists.

[the tree]

Each atom decays completely or not at all. For carbon 14, there's about 4 = 4.3 × 10^22 atoms in a gram. Or if you prefer, 43,000,000,000,000,000,000,000 atoms in a gram. Half of them will decay, half will not. Eventually, you will end up with no atoms at all, or perhaps there might still be an atom when you'd "expect" to find half an atom.

This.

 

After one half-life, the probability of any individual isotope having decayed is 0.5.

 

Strictly speaking it's only really called an atom when it has the right number of electrons to neutrons. A carbon-13 isotope has one too many neutrons which makes it unstable so it breaks apart.

 

Exactly when this will happen is impossible to predict (like, literally impossible - quantum indeterminacy kicks in on this scale) which is why half-lives which are really just a statistical average are used to predict how many out of a large number isotopes will have decayed after a given amount of time.

[ewmon]

Exactly when this will happen is impossible to predict

 

Oh ... I thought we could just take the derivative of the exponential decay ...

 

So, if a Carbon-14 isotope has a 50% probability of decaying every 5,730 years, then it has about a 1.2% chance of decaying every 100 years.

[Mr Skeptic]

Right, the chance of decay is constant at all times. However, that does not tell you when it will decay. You can't say, 100 years from now, these 6 atoms will decay and these 500 other atoms will not.

[swansont]

You don't end up with half an atom, but it now carries half of its energy

 

Um, no.

[lnm]

I am very thankful for every reply but I am still sort of confused. What, exactly, is radioactive decay?

 

What is it that happens to an atom? Does it loose an electron/proton/neutron and is now a different element/isotope? Does the speed of any particle in it slow down and this is what a lose of energy means? Does a particle in it evaporate and ultimately I would end up with no atom at all?

 

I am more interested in what is actually happening than in when it will happen or what the probability of it occurring is.

[Moontanman]

I am very thankful for every reply but I am still sort of confused. What, exactly, is radioactive decay?

 

http://en.wikipedia.org/wiki/Radioactive_decay

 

What is it that happens to an atom? Does it loose an electron/proton/neutron and is now a different element/isotope? Does the speed of any particle in it slow down and this is what a lose of energy means? Does a particle in it evaporate and ultimately I would end up with no atom at all?

 

An atom emits one or more of several particles, resulting in a new atom of either lower energy or a different element and lower energy. In some atoms they do indeed split into two smaller atoms but more often a particle of some sort is emitted. if the process continued on down to it's lowest possible denominator you would end up with a hydrogen atom, protons are believed to be ultimately stable.

[Sisyphus]

Does it loose an electron/proton/neutron and is now a different element/isotope?

 

This one. And by "lose" it should be noted that whatever is lost doesn't just disappear - it is ejected. So for example, the nucleus of carbon-14 has 6 protons and 8 neutrons. One of the neutrons breaks apart into a proton and an electron, and the electron is emitted, leaving behind 7 protons and 7 neutrons: nitrogen-14.

[TheLivingMartyr]

I am very thankful for every reply but I am still sort of confused. What, exactly, is radioactive decay?

 

What happens to the atom of a radioisotope (an element with a different number of neutrons, making it unstable) is that it emits radiation. the types of radiation are:

 

Alpha: the nucleus emits a helium nucleus (2 protons, 2 neutrons, with no electrons) this obviously means that the atomic mass of the element decreases by 4

 

Beta: the atom emits an e- particle (an electron)

 

Gamma: the atom emits gamma rays (photons, and this form of radiation occurs along side alpha radiation)

 

if you would like me to explain what these certain types of radiation can do, then i will be happy to:-)

[swansont]

What happens to the atom of a radioisotope (an element with a different number of neutrons, making it unstable) is that it emits radiation. the types of radiation are:

 

Alpha: the nucleus emits a helium nucleus (2 protons, 2 neutrons, with no electrons) this obviously means that the atomic mass of the element decreases by 4

 

Beta: the atom emits an e- particle (an electron)

 

Gamma: the atom emits gamma rays (photons, and this form of radiation occurs along side alpha radiation)

 

if you would like me to explain what these certain types of radiation can do, then i will be happy to:-)

 

Beta decay also emits a neutrino or antineutrino.

 

Gamma radiation is emitted with beta decays as well; alpha decays often leave the system in the ground state with no gamma emission.

[TheLivingMartyr]

doesn't it emit a neutrino by converting one of it's neutrons into a proton by emitting an electron and a neutrino?

[swansont]

doesn't it emit a neutrino by converting one of it's neutrons into a proton by emitting an electron and a neutrino?

 

electron and antineutrino for beta -, positron and neutrino for beta +

[TheLivingMartyr]

okay thanx

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i'm assuming that it's an electron neutrino? not for some random reason a muon or tauon neutrino

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oooo, i found a good feynmann diagram that explains Beta- decay

 

http://upload.wikimedia.org/wikipedia/commons/8/89/Beta_Negative_Decay.svg

 

the down quark of the neutrons decays into an up quark, by emitting a W- boson, which then decays into an electron and an electron neutrino

Edited May 20, 2010 by TheLivingMartyr
Consecutive posts merged.