# Electrical neutrality in radioactive decay

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1. Jan 27, 2015

### bwana

Although it was drummed into me that electrical neutrality is preserved, I am perplexed by the phenomenon of radioactive decay. How is electrical neutrality maintained when electrons (beta particles) and proton-neutron sets (alpha particles) are being spit out by some elements. These particles are whizzing by all the other neutral particles - how do they maintaintain their neutrality.?

2. Jan 27, 2015

### Vagn

$\beta^-$ emission occurs when a neutron in the nucleus decays into a proton by emitting an electron (and an electron antineutrino). The nucleus gains a charge of +e to compensate for that of the electron, as seen in the equation below:
$^{14}_{6}C \rightarrow ^{14}_{7}N + e^-$

In $\alpha$ decay a part of the nucleus is emitted, causing the number of protons to change, which changes the element of the daughter nuclide, as in the example below:

$^{238}_{92}U \rightarrow ^{234}_{90} Th + ^{4}_{2}He$

When these decays happen there is a corresponding change in the charge of the decayed nucleus.

3. Jan 27, 2015

### Staff: Mentor

What do you mean with "maintaintain their neutrality"? Overall, the total charge is conserved in each decay process. Locally, fast charged decay products can give a tiny re-distribution of charges, normally this quickly gets neutral again from tiny current flows.

4. Jan 29, 2015

### bwana

Yes, I'll be more graphic and maybe you can see my confusion. An electron leaves an atom. The nucleus of the atom gains a positive charge. The electron has gone off into space. First of all, are not free electrons labile? Do they actually live forever? I know that electrical current in metals consists of 'free' electrons, but that electron cloud is in a matrix of atoms. Although those electrons are free to move, they are in the vicinity of their atoms and so neutrality is preserved. Electrons in space have no 'matrix'. The electromagnetic repulsion by their field is enormous - do they ever slow down into a brownian motion sort of random behavior after bumping into so many atoms? What if they never run into any positive ions to be captured?

And what of the scorned nucleus that was abandoned by its electron? Does that atom (which is now a positively charged ion) go around looking for an electron to steal from some other hapless atom? Or does it just decay by giving off a proton? How does it neutralize its charge? The nuclear strong force is 130x greater than the electromagnetic force so I understand why the nucleus does not just fall apart. Does that positively charged ion just live forever? Does that nitrogen pictured in the equation above become a positively charged material? Can it be used as a power source in a battery because it is positively charged ?

The same concerns apply to alpha particles? What happens to the negatively charged atoms they leave behind? Is there an accompanying beta decay to balance out the atom?

Sorry for so many questions, I realize that the answers to these questions resides in data from experiments that are over a hundred years old. I just do not know how to search for the answers. Search engines tends to give a superficial explanation that is often a tautology.

5. Jan 29, 2015

### ChrisVer

Most of your questions are a tautology ...
What will happen to a free electrically-charged particle that is somewhere in the space? It's going to attract or be attracted to some other opposite-charged particle, to accomplish neutrality.
Also no matter how you rephrase things, the conservation of charge is obeyed by the reactions you ask for. You can't take a nucleus (that is positively charged +ZQ already) and ask why do I get 2 protons (alpha particle) out of it, you already had Z in there....

Also there charge conservation happens when you take into account the whole space. Not just some point where you can have an excess of charge... That's what the continuity equation tells you...

6. Jan 29, 2015

### bwana

So every alpha decay is accompanied by two beta decays? Simultaneously ?

7. Jan 29, 2015

### ChrisVer

$Z$ protons to your mother-nucleus and $Z-2$ + alpha particle $Z=2$ protons to your daughter products.
$Z$ electrons and then you have $Z$ again .... the result is that [even if the atom was not ionized by the process] you have an product with Z-2 protons and Z electrons (total charge = -2 , so in general it will prefer to shoot out the electrons) and an alpha particle going away (total charge=+2) .... Totally charge=2 -2 =0 ...
The alpha particle will eventually slow down at some point, and recapture some electrons to get neutral, because that's how it will achieve the least energy.

8. Jan 29, 2015

### bwana

You said 'no' but then you said 2 electrons would shoot out . To my mind that means an alpha decay is accompanied by two beta decays. Why did you say no?

9. Jan 29, 2015

### ChrisVer

shoot out from the resulting atom ... What I described is not a beta decay, it's an electron emission/atom ionization.

Do you know the difference between nuclei and atoms?

10. Jan 29, 2015

### Staff: Mentor

Electrons are stable. The electron will slow down from collisions with atoms, eventually become a thermal electron (= with an energy based on the temperature of the material) and join the huge collection of electrons around it.
The ionized atom will usually get an electron from its environment, becoming neutral while another atom might get charged for a while. Charged atoms (ions) are nothing unusual. Even without radioactivity, you have a few of them everywhere. In common NaCl ("salt"), nearly all atoms are ions.

No. It might lose electrons (at low energy, they do not "shoot out"), but those are not beta decays.

11. Mar 21, 2015

### rithwik

so we have to consider this universe as a closed system and then we can say that electrical neutrality is maintained...right

12. Mar 21, 2015

### ChrisVer

Where did you see that mentioned here? We didn't mention anything about a closed/open-system universe.
If the universe started being neutral, then it'll remain neutral (because electric charge is a conserved quantity). If it wasn't neutral (I don't really like that idea but it's not a matter of liking or not) then it had some plurality in charged particles and these particles cannot find "partners" to join with. But a pair of opposite charged particles is energetically prefering to stay together.

13. Mar 22, 2015