Reply Sun 7 Oct, 2012 05:51 am
Hi, I was just wondering about beta decay (thus the title) and I discovered an aspect that I did not understand. Let's assume I have a fist-sized block of Magnesium-27 (unstable). With a half-life of 9 minutes, many of the Magnesium-27 atoms will start to undergo beta decay in the following equation:

27Mg --> 27Al + e-(electron) + ve-(electron antineutrino)

by a neutron turning into a proton. What I don't understand is that the resultant Aluminium-27 has 13 protons (with the latest addition) but only the original 12 electrons and this would make it a cation. This would be fine as there IS an extra electron produced, but that electron will be released eventually or else there would not be any radiation (neutrinos go through matter without affecting it). In theory, the block of magnesium would end up as a block of aluminium ions with a huge positive charge. Is that even possible? If not, how does it return to a neutral charge?

Please reply even if you don't know the answer because I really want to know some possible theories. Thanks in advance!
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Reply Sun 7 Oct, 2012 07:39 am
Yes it will if completly isolated. But that is still a long time--look a fist sized block of magnesium is, say, 100 grams. With Mg27 that's gonna be 3.70 gram moles. And each gram-mole is about 6.02E+23 gram atoms.

Mow as Mg27 has a half life of 9 minutes (540 seconds) it's specific activity (Natural logaritm of 2 divided by half life in seconds) is 0.00128 s-1.

Take the number of atoms in the mass and multiply it by the specific activity and you'll get an ion (in this case a positive charge change as beta electrons exit the mass) . This will be about 2.86E21 positive ions per seconds. As a coloumb this is 467 Ci/s or 467 amps. So the beta decay would be a pretty good battery for a short while (BTW space capsules on long space voyages use radioactive materials as atomic batteries--they use long halflife materials--Pu241 is a fav with a half life in the billions of years).

Note this assumes that the loss of electrons is perfect loss. For that to practically occur the magnesium mass would have to maximize surface area--as a charged aluminum ion will tend to reabsorb the beta electron and cancel the charge. The energy will then be converted pysically, probably as heat.
So mass geometry will have an effect on the atomic battery.

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Reply Sun 7 Oct, 2012 04:08 pm
wheee does +beta or -beta decay take you? have you seen a segrey on this?
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