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Author Topic: What determines the instability of the nuclei of atoms of different isotopes?  (Read 6666 times)

Offline Robcat

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Can someone tell me what controls the instability in atoms of certain isotopes? Is the activity internal or externally stimulate For?
I have a watch made by luminex which had a tritium activator of the zinc sulphide and which gives me as much light as I need to read at night
The light will reduce as the half life of 11 year ish of tritium decays.
Something causes the unstable activity in a constant unchanging rate.     WHAT?
« Last Edit: 10/06/2015 22:32:50 by chris »


 

Offline evan_au

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Re: Radioactive decay
« Reply #1 on: 09/06/2015 22:44:47 »
If you look at the rest-mass of the isotope and add up the rest-mass of the decay products, you will see that something is "missing". This corresponds to the energy released by the decay. This is popularly described by Einstein's well-known equation E=mc2.

If there is a large amount of mass missing, the decay is likely to occur sooner (on average), for a given decay type.

Some decay types rely on the weak nuclear force, which is much less likely to occur than events mediated by the strong nuclear force, so these decay types occur at a much slower rate.

While there is a good mathematical model of the "half-life" of a mass containing many radioactive nuclei, noone really knows what causes an individual nucleus to decay in a particular microsecond.
 

Offline chiralSPO

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Re: Radioactive decay
« Reply #2 on: 10/06/2015 01:36:22 »
Some isotopes that undergo weak-force mediated decay have half-lives that are influenced by being bombarded by neutrinos. For instance 37Cl (which is otherwise very stable) can convert to 37Ar and an electron when hit with an electron neutrino. This is one way to detect the flux of neutrinos from the sun (and some people are trying to use this to predict solar storms) http://iopscience.iop.org/0004-637X/496/1/505
http://www.economist.com/blogs/babbage/2012/08/neutrinos-and-solar-storms
« Last Edit: 10/06/2015 01:39:25 by chiralSPO »
 

Offline Robcat

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Re: Radioactive decay
« Reply #3 on: 10/06/2015 20:37:16 »
Fascinated to see that no one really knows why a particular atom decays !!
Could it be
External action
Time modification within the atom
Instability caused by neighbouring atoms of the same ilk?
Or?
Would like to know more!
 

Offline evan_au

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Re: Radioactive decay
« Reply #4 on: 10/06/2015 22:35:26 »
Quote from: robcat
no one really knows why a particular atom decays !!
When we talk about electrons changing orbitals to release photons (a very low-energy form of atomic decay), this is readily affected by external events, such as bumping into an adjacent atom, involvement in chemical reactions, flow of an electric current, or a passing photon in a laser.

However, the nucleus in an atom is well-shielded from other atoms by the surrounding clouds of electrons, and the strong and weak nuclear forces are fairly short range, so direct interactions with neighbouring atomic nuclei is unlikely. (One exception is in hydrogen fusion experiments, where the electrons are stripped away, and high temperatures are used to overcome the repulsion between the hydrogen nuclei.)

So instability in a nucleus can be triggered by external factors like absorbing a neutron in a nuclear reactor; this changes the nucleus to a different isotope, which has a much shorter half-life, causing it to decay immediately. There is also the neutrino interaction mentioned by ChiralSPO.

In theory, you could produce a gamma-ray laser (a "graser"?), but the nucleus is a very small target to hit with a gamma ray in order to stimulate emission of a coherent gamma ray, and there is little time in which you could build up a coherent wave before the entire substance disintegrates.

Scientists are trying to discover if the mysterious Dark Matter interacts with matter in some way - so far, no convincing evidence has been announced.

But, like the nucleus, we don't even know why an isolated, individual atom emits a photon at a particular time - we can only speak in probabilities.
 

Offline chiralSPO

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One thing that we don't necessarily know is whether the is a definite, discrete cause-effect situation for these types of processes, or if the probabilistic interpretation is most reflective of reality. It could be that there is a constant flux of some sort of particle that at any given instant has a certain chance of interacting with the nucleus and directly causing the decay (rare interaction, but every interaction causes a decay). Or it could be that there is no need for an interaction, and that there is just some probability that the nucleus will spontaneously decay with no outside (or inside) influence.

Luckily the math is the same for both models unless there is a variable "flux." This "flux model" appears to be relevant in the few cases of neutrino-induced, or muon-induced or gamma-ray induced decays, but it is entirely possible that there are also states that spontaneously change for no reason whatsoever (we just can't prove it)
 

Offline PmbPhy

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Quote from: Robcat
Can someone tell me what controls the instability in atoms of certain isotopes? Is the activity internal or externally stimulate For?
I have a watch made by luminex which had a tritium activator of the zinc sulphide and which gives me as much light as I need to read at night
The light will reduce as the half life of 11 year ish of tritium decays.
Something causes the unstable activity in a constant unchanging rate.     WHAT?
Here is a model of one of the forms of radioactive decay, namely alpha decay, proposed by Gamow in 192. An alpha particle is a the nucleus of a helium atom and thus consists solely of two protons and two neutrons. Basically its a quantum tunneling phenomena. Alpha decay happens when an alpha particle moves around inside the nucleus. The potential function of the nucleus is a function of the number of protons and the number of neutrons in the nucleus. Those particles are the source of the strong force and the electromagnetic force and thus determine the potential function that the alpha particle is moving in. The alpha particle is bouncing back and forth inside the nucleus. Every time it collides with the potential barrier there is a finite probability that it will tunnel through the barrier and escape thus resulting in alpha decay. If the total energy of the alpha particle inside the nucleus cannot be greater than zero then the nucleus is stable.

See http://en.wikipedia.org/wiki/Alpha_decay

Other decay mores occur for different reasons.
 

Offline evan_au

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Quote from: Robcat
no one really knows why a particular atom decays !!
Let's say you made a very powerful microscope that would let you peer at all the nucleons jiggling around inside the nucleus, so you could predict exactly when a particular nucleus was going to decay.

Unfortunately, as often happens in the quantum world, any attempt to precisely measure the position and energy of the nucleons will change the way they jiggle, and will invalidate any predictions that you make based on the measurements.

The Heisenberg uncertainty principle is much more rigorous about the fundamental limits of our knowledge about the quantum world.
 

Offline PmbPhy

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Re: Radioactive decay
« Reply #8 on: 11/06/2015 13:23:11 »
Quote from: Robcat
Fascinated to see that no one really knows why a particular atom decays !!
That's not really the case. It's not that we don't know why but that its unknowable in principle and we know that. Nature is indeterminate in principle.
 

Offline Robcat

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Although I can't find thru BBC archives , I remember on tomorrow's world or some similar programme a demo of radioactive decay
The experiment shown was a disc similar to a CD which was impregnated with a radioactive iron isotope.
The disc At one point had a counter measuring counts per sec
The disc was spun at extreme rpm and the counts per sec increased.

I was always fascinated by this demo
Is there anyone who saw that demo on TV or can explain the resultant increased cps?
 

Offline PmbPhy

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Quote from: Robcat
Can someone tell me what controls the instability in atoms of certain isotopes?
I didn't think of this before but I think that now I have a better idea of what you wanted to know.

There is a balance inside the nucleus that keeps it stable and that's the number of protons and neutrons. If the ratio of protons to neutrons is wrong or if the nucleus is too big then it will be unstable. The protons are trying to fly apart due to the repulsive electric force while the neutrons work to hold it together by the strong force. However a nucleus with too many neutrons will be unstable. I forgot why but will get back to you on this.
 

Offline evan_au

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Quote from: PmbPhy
a nucleus with too many neutrons will be unstable
One way of looking at the energy of the nucleus is to view it as having shells similar to the electrons in an atom. When you fill one shell, you start filling the next shell.

The protons have one set of shells, and the neutrons have their own set of shells.

When you have too many neutrons in the atom, they start to fill higher shells while leaving lower proton shells empty. You can actually release energy by expelling an electron=beta particle (and a neutrino), converting a neutron into a proton, which can then fall into a lower shell, releasing energy in the form of a gamma ray.
 

Offline PmbPhy

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Quote from: evan_au
One way of looking at the energy of the nucleus is to view it as having shells similar to the electrons in an atom. When you fill one shell, you start filling the next shell.

The protons have one set of shells, and the neutrons have their own set of shells.

When you have too many neutrons in the atom, they start to fill higher shells while leaving lower proton shells empty. You can actually release energy by expelling an electron=beta particle (and a neutrino), converting a neutron into a proton, which can then fall into a lower shell, releasing energy in the form of a gamma ray.
I'm quite familiar with that Evan and didn't ask about it. Why are you so concerned about energy when this is about stability? Granted, energy considerations must be taken into account but I don't see why you posted that in response to my post.
 

Offline evan_au

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Quote from: PmbPhy
Why are you so concerned about energy when this is about stability?
If the proton & neutron shells are full to a similar extent, then it takes energy to convert of neutron to a proton. Since these large quantities of energy are not readily available within the nucleus, the nucleus will be stable.

To a large extent, the stability of an atom is determined by Energy considerations:
  • If a nucleus is in the lowest energy state, and all surrounding states have a higher energy, that nucleus will be stable.
  • If there is an adjacent, reachable state with a lower energy, the atom is likely to decay into that state, at a rate determined by the energy in the environment, and the size of the quantum well blocking the transition. 
 

Offline PmbPhy

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Quote from: PmbPhy
Why are you so concerned about energy when this is about stability?
If the proton & neutron shells are full to a similar extent, then it takes energy to convert of neutron to a proton. Since these large quantities of energy are not readily available within the nucleus, the nucleus will be stable.

To a large extent, the stability of an atom is determined by Energy considerations:
  • If a nucleus is in the lowest energy state, and all surrounding states have a higher energy, that nucleus will be stable.
  • If there is an adjacent, reachable state with a lower energy, the atom is likely to decay into that state, at a rate determined by the energy in the environment, and the size of the quantum well blocking the transition. 
So why did you post it as a response to a post of mine?
 

Offline Robcat

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Thanks folks, interesting discussion
I know the larger the atom, the more unstable it could be but my question started with my tritium illuminated luminox watch.
Gold atoms isotopes can be very stable but yes as the atomic number rises the stability clearly decreases.

My question really was about the time overall, of my relatively small tritium atom.  The question is basically what controls the time of a single atoms decay, without just using the word probability!

The question is whether the decay TIME, is externally activated by say neutrinos externally, or some magic internal clock linked to the packing fraction or just like the Higgs particle for Mass there being a Robcat type particle, that is TIME related within the atom?
 

Offline Robcat

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It's June 30 th and a leap second is being used because of the atomic clock
Nice to rely on this stable decay!
 

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