The Best Candidate for OU Prize

[MileHigh]

Xaero:

I think that you have made a lot of great points and did some energy and power crunching that I was not going to look up myself.

The bottom line is that Cuttingedge's idea most likely in principle can be developed, but cannot ever become something that would be practical.  Not by a longshot.

Cuttingedge:

Assuming that the only practical way to produce Tritium is by extracting heavy water from ordinary water in a heavy water plant - then it would take millions or billions of times more energy to produce the Tritium than you could extract from it.  Nonetheless, your idea is an interesting thought experiment.

MileHigh

[Xaero_Vincent]

You're right that tritium is impractical for solar applications but its being proposed as fuel for nuclear batteries that can power portable electronics. However, the rarity of the gas and difficulty of producing it will pose big issues for mass consumption.

Rubidium has overwhelming advantages compared to tritium and the element exists freely in nature but there are a few drawbacks as well.

Rubidium-87, while a weak beta emitter compared to many other isotopes is about 15x more energetic than tritium. This means that the radiation hazard is slightly greater but isn't so energetic that it cannot be shielded in much the same way.

Its a reactive element and ignites in water and moist air. The element is typically distributed in sealed vials. Light emitting vials would also be sealed so this isn't really a problem unless the vials were shattered.

[Xaero_Vincent]

An alternative to using highly-reactive rubidium might be indium.

Indium-115 is the most common isotope (95%), isn't reactive with water and air and non-toxic (aside from radioactivity), has twice the decay energy of 87Rb (B- 495 keV) into stable Tin-115 and has a ridiculously long half-life of 441 trillion years.

The disadvantage is that the element is far less abundant and is listed as the 61st most abundant element on Earth. However, it is 3x more abundant than silver.

[onthecuttingedge2005]

I never heard of 32Si being used for betavoltaic lighting but if it beta decays then it will work if it were coated with phosphor. How dangerous is the radioactive emissions though? Radium was used before tritium and light emitted from it would last well over 3000 years (half-life is 1600 years) but it caused bone cancer and therefore most countries banned its use for this purpose.

Understand that tritium is among the least dangerous radioactive isotopes and even so there is a import ban on it in the USA. 12x more light output might be enough for a solar panel (even though its still far less than the sun) but it would only make sense for a high-efficiency multi-junction panel with hybrid Sun use to make the idea cost effective. Multi-junction would be necessary so that it can be tuned for the light wavelength of the 32Si light emission and also the Sun's visible wavelengths for daytime use.

hi Xaero.

did you know that 60Co produces about 20 times the suns lumen energy per square meter on the ground per oz in invisible gamma radiation(if you could see it). 1 oz of 60Co will kill all life including tree's within a 1000 foot radius exposure over a given amount of time. you have to be careful here. it has to be calculated right.

at these energies you have to calculate gamma energies produced by B- collision releasing gamma radiation due to hardened shielding, softer shielding may not give off gamma, while hardened may. I think it has to do with the conductive electron in the shieldings band gap, when a high energy 60Co beta- particle hits the conductive electron it interacts with it releasing a gamma ray. so hardened shielding in this case actually increases radiation levels in the gamma ray spectrum rather than Beta-. 60Co's own conductive electron band gap may interact with its own Beta- decay and also emit a gamma ray. so it is best to leave these higher beta- energy levels to scientific labs.

60Co is the extreme upper limit that is to dangerous to incorporate. very intense. the half life of an Isotope has a lot to due with how dangerous it is because the element with shorter half lives disintegrate into energy faster and release higher energy densities that can be on the verge of SF or spontaneous fission. especially if the isotope is in the seconds half life range. even a half life of days is extremely nasty stuff. you could imagine 1 pound of solid matter being converted to Beta decay(electrons) in 5.271 years. that's a lot of harvestable electrons.

Jerry

[onthecuttingedge2005]

here is a nice little article on Betavolataics.

http://www.ece.rochester.edu/projects/FauchetGroup/Publications/Files/Sun/PublishedAdvancedMaterials.pdf

Jerry