Sciencemadness Discussion Board

Question about Beta Decay.

bolbol - 4-2-2015 at 20:36

I have never learnt much about nuclear chemistry so this might be a really stupid question. When I learnt about the basic types of decay I always questioned about the remaining products after a beta decay occurs.

So from what I learned, when beta decay occurs a neutron in the nucleus of the sample atom converts to a proton while ejecting the electron out of the atom.

Lets say we have a mole of this element and by the time the half life is reached half of this sample should have given up an electron and this would leave the nuclei of these atom with a nucleus that holds an extra proton and gives the whole atom a charge of +1. And since ions cant exist as solids.. how does this even work? How can half the solid sample have atoms with a +1 charge.



[Edited on 5-2-2015 by bolbol]

Chemosynthesis - 5-2-2015 at 02:53

First, you're describing beta minus decay, just in case you're curious. There are other form(s) to consider later. This interconversion is essentially the canonical nuclear phys/chem explanation, and it does produce ions in the sense that the atom is no longer in ground state. Usually, this results in metastable or instable states and is resolved in other nuclear reactions like Auger electron capture, a (second?) internal conversion, etc. If you really want to get into it, this can become more complicated with different electron interactions, and there are models to describe multi-electron ionization, such as the "shake off" model with "direct collision" correction.

It's important to remember that not all the atoms in a sample are converting simultaneously, so some questions of state can be troublesome since the state of a material is more of a bulk property of material (how many atoms does it take to make a gas? A liquid? Solid? How close?), and the daughter nuclides can be trapped in a lattice. It may be important to note also that this radiation is considered ionizing, but the on the other end of the reaction, the resultant bond damage that can be accrued to material such as DNA isn't really thought of as vaporizing it either, as free radicals and other particles are so reactive. It's an excellent question on states I'm not really qualified to answer (I believe someone in mesophysics and/or chemistry would probably be very useful), but I hope this was somewhat helpful even in dancing around the specifics of the last part.

fluorescence - 5-2-2015 at 03:35

Not really an expert on beta decay, too and it is somewhat complicated since you have to take the weak interaction into this, too.

So, if you have the Beta(-) Decay ( that's your example ) ...ehm...you have a conversion from neutron to proton. And your were right, you ejected a electron, too.

So from a mathematical base this should be possible:

1) Charge:

neutron = proton + electron + anti-neutrino

0 = 1 - 1 + 0

or in form of quarks

d = up + electron + anti-neutrino

-1/3 = +1/3 -1 +0


2) Isospin:

d = up + electron + anti-neutrino

-1/2 = +1/2 - 1/2 - 1/2


So since proton and neutron or up and down quark are the same particles with different isospins a conversion between the two of them is possible.

The ejected electron will probably face bremsstrahlung.

For the remaining atom, it's an interesting question since usually a stable isotope is formed after beta decay. Electron capture would be one idea but if that happens you'll get another element and that is not the case according to the table of nucleides.

Might probably be some kind of auger-effect like Chemosynthesis said. But nice question, I'll ask that a professor of mine.

Chemosynthesis - 5-2-2015 at 04:59

I'm going to try to avoid Standard Model fermions and leptons in a slight addendum to my first post, but I did also want to state that not only are there some free protons and electrons zipping around for ions to pick up (very stable half-lives, while free neutrons have easily observable half-lives), but nuclear decay is often not very clean in that you often (I hate to say always) get probability distributions of different daughter nuclides. The experimentals definitely get weird since people run into issues of how pure a scientific sample can even really be. It used to be that I would write off orbital filling by mentioning how easy it is to get static charge separation, but apparently some aspects of that are being questions, and we've known about static electricity for longer than we've known about radioactivity!
http://www.sciencemag.org/content/333/6040/308.abstract

careysub - 5-2-2015 at 10:02

I think the OPs question is of a much simpler, more fundamental nature.

An atomic nucleus, consisting of protons and (in all but one case) neutrons already has a positive charge. It is surrounded by a cloud of electrons so the net charge of the atom is typically zero in a non-ionic solid (charge separation can still occur). And yes ions can definitely exist as solids - take table salt.

When negative beta decay occurs, a neutron turns into a proton, changing the already existing nucleus positive charge of the nucleus. The electron is ejected, and wanders around in the solid, but some other electron will replace it to make the local charge in the region of the nucleus zero again. The nucleus, having changed to a different element will interact with the surrouding atoms in a different fashion of course (N-14, created by the decay of C-14 is generally no longer bound to the matrix of the original solid).

neptunium - 5-2-2015 at 11:37

i think the confusion comes from looking at the sample decaying as a whole and the decay as a one time event (as Chemosynthesis mentioned)
But no atoms or group of atoms exist in a vacuum! there is always ions and charges passing by and other atoms from the air arround the sample or the glass it is stored in ( as Careysub pointed out)
An hypothetical block of Sr90 floating arround between here and the Andromeda galaxy in a very deep vacuum would eventually be hit by a gamma ray or a proton or a cosmic dust to exchange ions with.
And even within this pure experiemental thought sample of Strontium in space, not all decay happened at once and other atoms pick up free electron in a manner that would not allowed the build up of charges and accumulation free radicals!

macckone - 5-2-2015 at 11:39

To answer the op question of static charge,
Yes materials can develop significant static charge
Due to beta decay. This will equalize with time due
To electrons ejected causing a negative static field
Around the sample and electrons migrating into
The sample. In some case you may get visible static
Discharge during equalization. Neutrons, alpha particles
Gamma radiation can also cause static ionization
By dislocating electrons. And in the case of alpha
Decay and beta+ decay moving positive charge
Away from the source.

bolbol - 5-2-2015 at 20:43

Quote: Originally posted by careysub  
I think the OPs question is of a much simpler, more fundamental nature.

An atomic nucleus, consisting of protons and (in all but one case) neutrons already has a positive charge. It is surrounded by a cloud of electrons so the net charge of the atom is typically zero in a non-ionic solid (charge separation can still occur). And yes ions can definitely exist as solids - take table salt.

When negative beta decay occurs, a neutron turns into a proton, changing the already existing nucleus positive charge of the nucleus. The electron is ejected, and wanders around in the solid, but some other electron will replace it to make the local charge in the region of the nucleus zero again. The nucleus, having changed to a different element will interact with the surrouding atoms in a different fashion of course (N-14, created by the decay of C-14 is generally no longer bound to the matrix of the original solid).


in what way would it make the local charge of the nucleus zero? If an electron was added to the electrol cloud of the atom from elsewhere it would stabilize the charges, however with that it would also change the atom to an atom of another element, right? And if the the other electrion from the outside was to combine with a proton to make a neutron then even in that case it would be a reverse of the beta decay so... idk does this even make sense? I am not familiar at all with nuclear stuff but this is what I think when I try to combine the logic of it with what I currently know

violet sin - 5-2-2015 at 22:12

the beta decay kicks out the decay product electron at high speed, however the electron that migrates in to balance the charge is standard speed relative to the other material. it doesn't re-combine in the nucleus. just hangs out in it's shell like normal.

phlogiston - 6-2-2015 at 02:35

Yes, you get charge separation. The ejected electron speeds off and the remaining block of material is left with a positive charge.

This effect has even been used as a direct source of electrical power. Capture the electrons on an electrode and you have a battery with a huge voltage (but tiny current).

Theoretically, I guess if the rate of charge buildup in the isotope was absolutely enourmous in a very short period of time, you could conceivably get a coulomb explosion (ie. due to electrostatic replusion between ions), but any compound that is so enormously radioactive for this to happen will (1) be impossible to manufacture at a fast enough rate and (2) melt and evaporate before you could assemble enough of it in a solid lump to see it explode.

For isotopes that decay at 'reasonable ' rates (that allow for experimentation), It is no different from other static charges that commonly occur all the time around you.

At the atomic level, in a conductive solid, the charges or holes can move around (be 'delocalized'), and you can't really pinpoint any atom that is an ion. In a non-conductive solid, yes you will have well defined ions. They can exist as solids. They will eventually acquire an electron from their surroundings (leaving another atom with a temporary deficiency).

careysub - 6-2-2015 at 09:50

Quote: Originally posted by bolbol  

in what way would it make the local charge of the nucleus zero?


I said local charge in the region of nucleus. This means the nucleus might be a charged ion (in an ionic solid) or have free electrons wandering around (in a metal) but there is no large scale net charge.
Quote:
If an electron was added to the electrol cloud of the atom from elsewhere it would stabilize the charges, however with that it would also change the atom to an atom of another element, right?


No. The only thing that determines which element a nucleus represents is the number of protons in the nucleus. Nothing else.
Quote:
And if the the other electrion from the outside was to combine with a proton to make a neutron then even in that case it would be a reverse of the beta decay so... idk does this even make sense?


This is called electron capture, and it is the inverse of beta decay, and some nuclides do undergo this process.

[Edited on 6-2-2015 by careysub]

bolbol - 6-2-2015 at 12:32

Okay it makes much much more sense now. Where do you learn this stuff mostly anyways? In quantum physics or physical chemistry?

phlogiston - 6-2-2015 at 13:21

High school physics classes, at least where I live.

[Edited on 6-2-2015 by phlogiston]

bolbol - 6-2-2015 at 14:49

Oh well never took a physics class.. lol

j_sum1 - 6-2-2015 at 16:23

Quote: Originally posted by phlogiston  
High school physics classes, at least where I live.

[Edited on 6-2-2015 by phlogiston]
Where? In Flatland?
(Well, I found that kind of funny!)

careysub - 6-2-2015 at 16:27

I learn this stuff by reading all the time.

I never really found school helpful in learning anything until graduate school (and then only at a really good school).