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Radionuclides instead of batteries?

  1. Sep 18, 2007 #1
    I know radioactive isotopes are used in RTG's in satelites and space probes. But are there any specific reason why they are not used in laptops, cellphones and other electronic equipment?

    From a environmental and health point of view It cant be any worse than using heavy metalls like Cadmium and Lead?
  2. jcsd
  3. Sep 18, 2007 #2


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    Well, you should probably work out the needed activities, but I'm pretty sure that you'll get a higher toxicity from the radio-elements than from the heavy metals for the same amount of power. So the main problem is the radiation shielding. Most radioactive decay is accompagnied by gamma emissions and you need a heavy material (lead) to shield you from it.

    Radioactive materials have a bad "power-to-toxicity" ratio, which you can deduce from the following fact: A few Grays as a flash dose is a dangerously and often deadly dose. Now, a Gray is a Joule per kilogram of deposited ionisation energy. That's a ridiculously low energy density. You'd need about 4000 Gray to heat water by 1 degree centigrade, but by the time you got a dose of 4000 Gray, you're long dead.

    So as long as you can protect yourself from this radiation, this is fine, but don't expect to have a powerful battery "in the open" which doesn't harm.
  4. Sep 18, 2007 #3
    What Vanesch said is pretty much the reason. In order to have enough energy to power the device, the activity of the radionuclide would require licensing by a regulatory agency, which is cost prohibitive.
  5. Sep 18, 2007 #4
    Its not that hard though to find for example fission products that decay without having any gamma emitters in the decay chain. I flipped through the table of isotopes today and found a few good candidates.

    If its just alpha and beta it doesnt matter how high the activity is from a health perspective, unless someone breaks the casing and swallows the nuke battery. Realisticly it will never lead to any significant radiation dosage. If its safe enough in a pacemaker it should be safe enough for a laptop or cellphone?

    But I can se how it would be a regulatory mess because of the overly stupid laws regarding radiation.
  6. Sep 18, 2007 #5


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    The power of a cardiac pacemaker is not signficant - it's mostly voltage pulse to get things going in the heart system.

    The power level for a power supply is different and would consequently have more radiation because of higher decay rate. The shielding would add weight to a laptop or PC.

    Also the microprocessor and memory chips can by zapped by radiation. For that reason, computers use on the Shuttle and ISS are based on large transistor architecture (P3) and even then they have to be periodically rebooted.

    Finally, because of the 'potential' hazard to health, radiation exposure must be limited and radioactive material must be controlled by responsible individuals.
  7. Sep 18, 2007 #6


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    Just curious, which ones you had in mind ?

    Well, for products for mass consumption, breaking the casing is something which is sooner or later going to happen ; erode away too. I agree with you that the shielding against alpha and beta radiation is not much of an issue, as long as you can guarantee the integrity of the enclosing. But in any case, to produce a significant amount of power, you need in any case dangerously high activities - dangerously in the sense of presenting a serious potential health hazard if completely out of control. Again, for specific applications, where people know what they are doing, it is doable, but not for large-scale mass consumption.

    Imagine a terrorist accumulating used cell phone batteries, grinding them to a fine powder and releasing it from a small airplane over a city or so...
  8. Sep 18, 2007 #7
    Ce-144 seems like a decent candidate at first glance(I couldnt find any info on how much of this is acctualy produced in fission though). Beta decaya to Pr-144 with a half life of 284 days and Q around 310keV.

    Pr-144 in turn beta decay to Nd-144 with a half life of 17 minutes and Q around 3MeV.

    Nd-144 in turn has a half life on the order of 10^15 years.

    Decay scheme for Ce-144
    http://www.nndc.bnl.gov/chart/getdecayscheme.jsp?nucleus=144PR&dsid=144ce bM decay&unc=nds

    Roughly 1,2*1+^14Bq/gram which gives a power of(in equilibrium with Pr-144) 56Watt/g. Maby some order of magnitude off but something like that.

    Offcourse the two beta branches that end in excited states of Pr-144 is a problem. But there is no gammas above 100keV atleast. I havent bothered to calculate the activity of the gamma and how much of a problem it would be. Just brainstormed with another student buddy.

    I am one of those with the oppinion that the laws on radiation are unbalanced compared to laws regarding chemicals. Sometime somewhere a casing will break, that is true. But will it happen enough times for it to be a problem and what is the acctualy risk involved when a casing breaks?

    It might be to risky, depends on how chemicaly stable the desired isotope is and how stable the decay daughers are. How safe can the sealing be made. I have no experience with that so Im just speculating as you can probably tell :)

    That depends on the ammount needed to pose a health hazard or more importantly warrant a expensive cleanup. It it something on the order of 1000Ci or is it more like 100 000Ci. If its the former then I can se that the battiers would be a terror threath, if its the later I dont se it as more of a threat then say all those chlorine trucks that drive around unprotected?
  9. Sep 18, 2007 #8


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    Right, and in 11% of the cases, you get also a 133 KeV gamma ray...

    Yup, and with a 0.7% case of a 2.2 MeV gamma emission if I'm not misreading the decay scheme.
  10. Sep 18, 2007 #9
    I missed that sucker :(

    Hmm I might be missreading the scheme but isnt 97,9% of the decays GS->GS and only 1.05% to the state that gamma decays with the energy you mention? I guess 1% is more than enough though with that energy, I completely missed that one.

    Edit I thought you said 7% not 0.7%, my bad.
  11. Sep 24, 2007 #10
    The main problem is still licensing. For just about most alpha emitters, possession greater than 1 microcurie (which wouldn't be enough to really power much of anything I imagine) requires licensing, unless the NRC changes their regulations and allows them to be generally licensed (i.e., anyone can buy them). Most alpha emitters don't even have a quantity listed as exempt from licensing (see 10 CFR 30) and therefore require a license. For beta and gamma emitters, you can probably go up to about 100 microcuries for most sources (some even go up to 1 millicurie, but those are usually low energy or very short half life nuclides such as tritium or F-18), but then you run into the shielding problem again. Also, any sealed sources with half life greater than (usually) 30 days or that are entirely gaseous, such as what you suggest, greater than 10 microcuries of alpha (100 microcuries for beta/gamma emitters) also require sealed source leak testing, which would be cumbersome for the average consumer (requires an analyzer of some type, costing seevral hundred dollars.)

    All of this, of course, is simply the financial aspect, which would prevent the possibility of this in the first place.
  12. Sep 24, 2007 #11
    taking a look at this one (Ce-144), the specific activity of this is about 3200 curies per gram, and the activity exempt from licensing requirements is 1 microcurie. This works out to about 17.5 nanowatts for the battery.
  13. Sep 24, 2007 #12


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    Just to add to what you say above; it is insructive to look at the design of the Voyager spacecraft:


    The RTGs - are located on a boom [ the "arm" at the bottom of the diagram ] that holds the RTGs
    away from the main "hub" of the spacecraft - and away from the instruments which are on their own
    boom on the opposite side of the spacecraft.

    Dr. Gregory Greenman
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