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Betavoltaic batteries are devices which creates electricity from beta radiation of a radioactive material. Alphavoltaics operate similarly, using alpha radiation. The concept was invented roughly 50 years ago and they are safe enough to be used, for example, in pacemakers.

However, the Wikipedia article on them states that they were "phased out as cheaper lithium-ion batteries were developed." I feel, though, that lithium ion batteries are hardly up to the task that consumers would want them to perform: for instance, iPhones hold their charge for about a day and notebooks can sometimes manage no more than four hours. Betavoltaics, on the other hand, can hold their charge for years.

Why, then, are they not used in commercial applications? What are their relative advantages and disadvantages with respect to the current solutions, and in particular to lithium ion batteries?

UPDATE

Amount of electricity is tied with half-life. For example, if Ni-63 has half-life of 100 years this means, that mole of Nickel will produce Avogadro/2 electrons during that 100 years. This means 10^21 electrons per year and 10^14 electrons per second.

This means up to 0.1 mA or electric current.

The energy of electrons from Nickel is 67 keV. This means that each electron has 67 kilovolts of electric tension.

So, the power of electricity from one mole of Nickel-63 is 67000*0.0001 = up to 6 watts.

Other way to calculate. If Nickel-64 produces 10^14 electrons per second, each of 67 keV of energy, then the power is 7 * 10^4 * 10^14 ev/s = 7 * 10^4 * 10^14 * 10^(-19) = 0.7 Watts.

So, the numbers are consistent to the order of magnitude.

Approximating, one mole of Nickel-63 provides 1 watt of electricity approx.

This looks sufficient for many cases including iPhone power consumption.

1 mole of Nickel-63 weights 63 grams. iPhones accumulator can weight more than 100.

So atomic batteries can supersede conventional batteries, and serve for years.

So why we don't use them?

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I guess that they don't have an output power that's high enough while maintaining safe radiation levels. –  Lagerbaer Nov 8 '13 at 16:08
    
Do you have any confirmations? For beta emission radiation is turned directly to electricity. Beta particles are just electrons. Theoretically it is possible to make all that electrons useful, hence no radiation at all. If some leak, then good shield should help. Beta particles can't travel through solid metals. I was thinking that they didn't invent good material yet, but saw no notes about this in Wikipedia. –  Suzan Cioc Nov 8 '13 at 16:19

2 Answers 2

up vote 10 down vote accepted

There are many reasons for this situation.

  1. Power produced is non-adjustable. The battery produces power at nearly constant rate (slowly decaying with time). It cannot be increased and if not consumed (or stored) the power is lost.

  2. (Mentioned by DumpsterDoofus) low power density. ${}^{63}\text{Ni}$ for instance produces ~5 W/kg (and kg here is just mass of radioactive material, the actual battery would be at least order of magnitude heavier). There are, of course isotopes with power densities much higher but they encounter other problems.

  3. Semiconductor damage. If we try to increase power by using isotopes with higher decay energies we find that the high energy electrons damage semiconductors, reducing service life of batteries to times much shorter than isotope halflife. Alpha particles, especially, damage the p-n junctions, so even though (for instance) ${}^{238}\text{Pu}$ produces 0.55 W/g of alpha radiation, it is mainly used in the thermoelectric schemes rather than in direct energy converters.

  4. Gamma radiation. Many isotopes has gamma emission as a secondary mode of decay. Since this type of radiation is difficult to shield, this means that the selection of isotopes usable for batteries is limited only to pure beta emitters.

  5. Bremsstrahlung. Electrons braking produces this type of radiation, that had to be shielded. Again, this limits our selection of isotopes to those with relatively low decay energies.

  6. Low volume of production / Economics. Many isotopes cost too much to be practical in wide array of applications. This is partly explained by low volume of production and partly by production process which will be costly at all volumes because it requires energy consuming isotope separation and special facilities for working with radioactive materials. For instance, tritium (one of the materials for betavoltaics) costs about $30 000 per gram and its world annual production is 400 g (from wikipedia).

All this means, that nuclear batteries are limited to a selection of niche applications, typically those with low power / long autonomous lifetime requirements. That is not to say that there can't be innovations expanding their use or reducing costs.

[1] Tsvetkov, L. A., et al. "Possible Way To Industrial Production of Nickel-63 and the Prospects of Its Use." (2005). online version

Update. Your updated calculations on power output from ${}^{63}\text{Ni}$ is essentially correct with one crucial distinction: 67 keV is total decay energy and approximately maximum energy of electron. But, since the decay also produces neutrino the mean energy of electron is much smaller: 17 keV (look at this NUDAT reference, or this java applet for electron spectrum). So the usable power from 1 mole of ${}^{63}\text{Ni}$ is: $$ W= {}^{63}\text{Ni specific activity} \times 17\,\text{keV} \times 63\,\text{g} = 0.36\,\text{W}, $$ where specific activity could be, for instance, taken from Wolfram Alpha. This is not sufficient to provide iPhone peak power consumption, which is about 1.5 W (see my reason 1).

Incidentally, we come to one more reason (though not, strictly speaking, related to physics):

  • Safety / Regulations / Perception: 63 grams of ${}^{63}\text{Ni}$ constitute more than 3500 curie of radioactivity, which would definitely require regulations for handling and probably would not be allowed inside a single unit for unrestricted civilian use. We know that when properly used betavoltaics are safe. But what about im-proper use / improper disposal / potential for abuse? At any rate, current perception of nuclear power by general public is not that good, so marketing nuclear batteries will present certain challenge.
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See my update. I can't agree with points 1-4. (1) it can be invented something. For example one can drain excess power during initial tima (2) power dencity of Ni-63 is not low (3) semiconductors are not obliged (4) no gamma decay in Ni-63; 5,6 looks solveable –  Suzan Cioc Nov 9 '13 at 18:36
    
@SuzanCioc: (1) something is invented: lithium battery. How about this idea: iPhone betavoltaic case - recharges your phone battery when it is idle. (2) See my edit. you were mistaken by a factor of ~3.8. (3) Sure, but this new technology for power conversion would neither be weightless, nor 100 % efficient (at least at first). I agree that for Ni-63 pts. (4-5) are moot. (6) Be my guest. –  user23660 Nov 10 '13 at 5:52
    
@SuzanCioc: To clarify: I am all for expanding the usage of betavoltaics, increasing ${}^{63}\text{Ni}$ production, reducing its price and creating new types of converters for alpha and beta radiation. I just listed some of the current problems which are not necessarily insurmountable. –  user23660 Nov 10 '13 at 6:00

They aren't used in iPods and laptops because they can't be used in them. A simple Google search for "betavoltaic power density" yields the answer to all three of your questions, cited below for convenience:

http://www.widetronix.com/products

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I don't see a word "density" anywhere on the page you linked. –  Suzan Cioc Nov 8 '13 at 17:07
2  
@SuzanCloc : The values of power listed on that page top out in the microwatt range, for something that you can hold in your hand. –  lionelbrits Nov 8 '13 at 19:58
    
@susancioc: Rehashing what "lionelbrits" said, the power densities are given on the page, and they are clearly on the order of a billion times lower than what is offered by current lithium technology offers. –  DumpsterDoofus Nov 8 '13 at 20:41
    
@lionelbrits I saw power values. But they use small tubes of gaseous tritium. Not strange that it produces small amounts of electrons. If we take solid material with more density -- we will get more. You wish to say that any beta emitter has low prodution? –  Suzan Cioc Nov 9 '13 at 9:19
2  
A answer here should be more than "Here's a link, go fish". This answer is basically a dressed up "Let me google that for you", which is inappropriate and doesn't belong here. –  Olin Lathrop Nov 9 '13 at 18:42

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