# What makes an atom unstable for radioactivity?

1. Sep 20, 2004

### NanakiXIII

I've been reading about radioactivity, but I can't seem to find what actually makes an atom unstable. Can anyone tell me?

2. Sep 20, 2004

### vlamir

This is very appreciable distinction, how physicists and chemists understand the word orbital.
At reading textbooks and articles by many authors-chemists each reader can find out, that chemists involuntarily (subconsciously) put the equal-sign between the words orbital and orbit of curvilinear movement.
I would like to bring for your attention some pictures, which "were drawn" with the mathematical program "MATHCAD".
During the whole year I occasionally look through these pictures and cannot understand, what benefit can be taken from these orbits and orbitals:
http://vlamir.nsk.ru/pt4_film.gif [Broken] (80.5Kb)
It is the closed resonant object, which has constant length. The amplitude of oscillations cannot be more than some limit n, which in scale is shown in figure
http://vlamir.nsk.ru/pt4xn.gif [Broken] (6.5Kb)
These two figures precisely correspond to experiment.
Attempts to increase amplitude of oscillations are ineffectual since for this purpose it is necessary to break off the orbit.
But the mathematical program makes it very simply.
In the following three figures the amplitude of oscillations is increased in six, twelve and twenty times, accordingly:
http://vlamir.nsk.ru/pt4x6.gif [Broken] (7.5Kb)
http://vlamir.nsk.ru/pt4x12.gif [Broken] (7.0Kb)
http://vlamir.nsk.ru/pt4x20.gif [Broken] (6.5Kb)
With the help of the polytronic equations we can create huge set of similar projections with various number of petals, which, as you see, are similar standard orbitals. My doubts in a reality and stability of these energy states of atoms are based that for creation of these conditions the atoms or their some parts should be destroyed. On the other hand, I should trust mathematics.
I think, the imposing of resonances is the main destructive force inside atoms.

Last edited by a moderator: May 1, 2017
3. Sep 20, 2004

### Creator

On a fundamental level, QED relates spontaneous decay directly to the fluctuations in the vacuum zero point field.

Creator

--"Ninety-nine percent of the lawyers give the rest a bad name".-- :rofl:

4. Sep 21, 2004

### marlon

The reason is the structure of the atomic nucleus. Some nuclei contain a lot of nucleons like protons and neutrons. This requires a lot of binding energy to hold such a heavy nucleus together. Sometimes nature will find a way to make things more easy on her and thus making the nucleus lighter by reducing the number of constituent nucleons. This is the decay. You will see for example that some heavy nuclei will decay into alpha-particles (which are just Helium atoms) because they are smaller and more stable then the original bigger and unstable mother-nucleus...

This is the reason...

Another way is that due to a collision with another particle, a certain atom get's excited. Now this is a unstable state, so nature decides that the atom will undergo de-excitation in order to become a stable atom in the "rest-state". this de-excitation occurs quantummechanically by emitting photons of certain energy. Thus, electromagnetic radiation is emitted.

regards
marlon

5. Sep 21, 2004

### NanakiXIII

Thanks for your replies, though I don't really understand the first. Thanks for your big reply, vlamir, but I really haven't a clue what you're talking about.

So an atom is unstable because it's big and thus harder to keep together? (I wasn't talking about colission)

But H-3 is unstable, right? But there are far bigger atoms than H-3 that are stable, aren't there?

6. Sep 21, 2004

### marlon

Correct, bigger is maybe a poor choice to express myself ,

i mean this : suppose you can place 10 electrons in a row. The most stable situations are these :

1) zero electrons (ofcourse this is not very interesting...)
2) 5 electrons (just half the row filled up)
3) 10 electrons (like the elements that have the socalled octet-structure)

Now if you have 6 electrons, this is not stable and nature will try to maintain 5 electrons and lose the sixth one. That is the picture. Now, ofcourse 10 electrons is a "bigger" atom yet it is more stabile.

Keep in mind that this is just an example. If we are talking about nuclei then we need to use nucleons in stead of electrons and they are not really placed in a row. That is just for explaining it, ok ???

Also don't pay to much attention to the number 10 i use. That is just for showing you what really happens...QM can calculate the number of electrons per energy-level.

regards
marlon

7. Sep 21, 2004

### humanino

The most stable of all nuclei if Fe56 :
here
For lighter nucleui, you can gain energy by fusion.
For heavier nuclei, you can gain energy by fission.

8. Sep 21, 2004

### humanino

or more relevantly here

9. Sep 21, 2004

### humanino

The nucleus binding is due to the residual strong interaction between quarks of different nucleons (=protons and neutrons). The nucleons exchange mesons, this results in an attractive force, usually winning against the EM repulsion between proton.

Now, what makes radioactivity ? It is the weak interaction turning one proton into one neutron, or only QM by itslef, via the tunnel effect : for instance, $$\alpha$$ radiation is due to the fact that the nucleus can "see" he could gain energy, that is like falling in a potential except that there is a barrier to cross, by rearranging the nucleons in new strongly-bound states.

10. Sep 21, 2004

### NanakiXIII

I meant bigger as in more protons and/or electrons in the nucleus.

I don't really understand the electron example, but...there are certain amounts of particles that are stable, while other amounts are not (or less)? Magic numbers? What exactly are Z and N? The numbers of neutrons and protons, I assume.

11. Sep 21, 2004

### humanino

The electron orbit very far from the nucleus compared the nucleus' size ! (5 orders of magnitude) Z=number of protons
N=number of nucleons = Z+number of neutrons
Magic numbers are due to the shell strucure of the nucleus, similar to the shell structure of electrons orbits. Nucleons arrange by pairs of the same type

12. Sep 21, 2004

### NanakiXIII

I see. Thanks. So why exactly are those numbers magical?

13. Sep 21, 2004

### marlon

Well because these numbers correspond to the amount of nucleons that form the most stable state.

Like in the electron-example...A certain number of nucleons on one energy-level is stabile (like all possible positions filled up or just half of them)

regards
marlon

14. Sep 21, 2004

### NanakiXIII

Yes, I understand that, but why do those amounts form the most stable state?

15. Sep 21, 2004

### humanino

I suggest you take a look at [thread=41110]this[/thread] where the nuclear cohesion is discussed. Especially this link.

I think it is either very easy : the magic numbers account for fulfilled shell of states; or much too complicated.

16. Sep 21, 2004

### Chronos

Try here for a pretty good explanation
In grossly simple terms, radiative emissions occur when the energies binding the atomic nucleus together are not sufficient to prevent it from falling to a lower energy state. This, in part, is why only very heavy elements are naturally radioactive.

Last edited by a moderator: Apr 21, 2017
17. Sep 21, 2004

### vlamir

Nan …, for me is impressed your intense interest to the given problem. You accent the question just the one its part, which has no an exhaustive explanation.
Attempts to explain stability of ones atoms and instability of others by means of collisions are too naive for our time. More or less satisfactory explanation the energy model gives, but it cannot explain the nature of intra-atomic energy. I hope, that in the given forum participate physicists and chemists, who search for own decision of a problem, therefore I expect more original ideas.
From my side I can offer the pair of "wild" ideas, for which I cannot find mathematical interpretation.
1) The solid shell of atom is capable to focus force properties of surrounding space in the central area of atom.
2) Probably, in the nature there is an identity vacuum = time.

As to stability of hydrogen and instability of tritium (and heavier H4), this distinction can be mathematically proved by multiple increases in internal energy of atom due to multiple increases in amplitude of resonant oscillations.

18. Sep 22, 2004

### marlon

Like I already said : this is because of the numbers of nucleons occupying a certain energylevel. The things I wrote in the electron-example are basic results of QM. I mean, these results are proven and that is it. Ofcourse You can keep on asking why are these results true ??? However this is not how physics is done. Physics tries to describe nature, it does not tell nature how it has to work nor does it EXPLAIN why nature behaves in a certain manner...

regards
marlon

19. Sep 22, 2004

### humanino

The stability of the proton would have been proven ? How did you achieve that ?

20. Sep 22, 2004

### marlon

What the hell is this all about ???

And what do you mean by the stability of the proton. Are you referring to the asymptotic freedom of the strong force ???

regards
marlon