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> Alpha Particles, Power source?
tekwiz
Posted: March 16, 2011 07:25 pm
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I've been looking into alpha particle radiation & I ran across something that described alpha emitters as "perpetual cathodes", because alpha particles are basically helium atoms lacking electrons.
Does this not imply that electric power can be produced by the flow of electrons as these particles capture electrons & become neutral helium atoms? Seems to me if this is the case, alpha emitters would make great nuclear batteries because alpha radiation is extremely easy to shield against.huh.gif


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AdamO
Posted: March 18, 2011 09:24 pm
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Without figures in front of me, I'd imagine that the kinetic energy typical of α-radiation (4-8MeV, which is still not much at all) makes the ionization potential of the He-4 nucleus pale in comparison.

Just a guess though.

-Adam O.
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tekwiz
Posted: March 18, 2011 09:31 pm
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QUOTE (AdamO @ March 18, 2011 12:24 pm)
Without figures in front of me, I'd imagine that the kinetic energy typical of α-radiation (4-8MeV, which is still not much at all) makes the ionization potential of the He-4 nucleus pale in comparison.

Just a guess though.

-Adam O.

Now that's interesting, because there are a few kinds of alpha powered nuclear batteries under development that employ that kinetic energy.
They do this by sandwiching a thin layer of alpha emitter between semiconductor layers that form a diode. The alpha particles knock electrons loose to form a current.
This implies that ionization power production does work, but is so weak as to be near useless. Whether this is true or not, I don't know.


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AdamO
Posted: March 18, 2011 09:45 pm
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It sounded to me like you were suggesting that the ionization potential of the He-4 nucleus could be used in a cell just like any redox reaction. Banging α-particles into other things to knock electrons off those other things and get a current is not the same thing, and, to me, seems like a more reasonable place to look for usable energy for the same reason I mentioned above.

-Adam O.
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tekwiz
Posted: March 18, 2011 09:55 pm
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QUOTE (AdamO @ March 18, 2011 12:45 pm)
It sounded to me like you were suggesting that the ionization potential of the He-4 nucleus could be used in a cell just like any redox reaction. Banging α-particles into other things to knock electrons off those other things and get a current is not the same thing, and, to me, seems like a more reasonable place to look for usable energy for the same reason I mentioned above.

-Adam O.

That is what I was suggesting...some alpha emitters produce a LOT of particles, each of which will soak up 2 electrons.
I saw a reference to an alpha emitter as a "perpetual cathode" which is what got me thinking along this line.


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CWB
Posted: March 19, 2011 01:39 pm
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some time back there was a topic (here , i believe) along a similar tack .
i (basically) asked about the idea of using radioactive material as a cathode (think tubes that don't need to be heated up) .
tim had some thoughts on the idea .


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Sch3mat1c
Posted: March 19, 2011 02:14 pm
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You get way more energy from the nuclear energy itself than the particle. Indeed you're a damnedfool if you think it's worth using the charge at all. It isn't.

A helium nucleus only has ca. 60 eV electron affinity, out of 4 MeV total, or 0.15%.

One downside is, you don't know which way the alphas are going, so it's hard to block them precisely. A point source inside a spherical shell seems reasonable.

One upside is, alphas are consistent in velocity, 3.5 to 4.5 MeV, each and every time (give or take energy lost to transport -- thin films are assumed). No matter which direction it goes, it must give up this energy somehow. Electric field is a fine method, so you'll simply end up with a ~2MV source with extraordinarily high output impedance (i.e., at 50% efficiency, 100W of Pu238 gives 2MV at 25uA). The characteristic should be very similar to a tube diode, i.e., at low voltage drops, most of the alphas zoom out and rebound from the very positive anode, forming a space charge. Many will steal electrons from the cathode (which is more negative resulting from the release of alphas), thus conserving charge in steady state (and wasting power). For larger voltage drops, the current will rise, until at some point (determined by geometry), it starts flattening out to a constant (saturation) current.

The same is true of a beta (electron) battery, but the voltage characteristic is more resistive, due to the spectrum of energies given off (~10 keV to 500 keV, depending on type).

Tim


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tekwiz
Posted: March 19, 2011 06:34 pm
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I wasn't thinking anong the lines of efficiency, but merely if it were possible. Seems it is.
I was wondering what the results would be if an alpha emitter was placed in close proximity to an incandescent surface & the two used as a source of electricity, possibly using magnetic flelds to funnel more particles where they would do the most good. Wouldn't the cloud of electrons surrounding any hot surface be attracted to the positively charged particles, thus creating a voltage potential & current source? I realize that the energy needed to heat the surface would be vastly greater than any resulting from charge balancing.


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For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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Sch3mat1c
Posted: March 22, 2011 01:38 am
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The energy of electrons given off by thermal emission is negligible versus the 4MeV of alphas.

A hot surface alone can be used as a power source but the efficiency is negligible. For instance, a 6AL5 dual diode might generate a few microamperes at fractional volts, while consuming 6.3V 0.3A.

Tim


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