Cf249.html: Decay: 6.295 MeV, Half life: 351 y, W/g after 110y = 0.122813

(Cm243 HL 29.1 y for 25 years battery at 29.5g)
(For fun: Cf251 or Am241 for 1000 years battery at 0.02 W/g after 1000y -
 1.3kg reqd for 30 W - maybe for emergency radio transmitters?. Ra would also
 work, and it's easy to get.)
 
245 g "battery" = 38 - 30 W. (Over the 110 year line)

Use Metal-halide or high pressure sodium lamps to get the most out of the
power from the battery. (Does any such lamp lasting for 100 years exist?)
Reddish light may be favored due to that it doesn't destroy night vision.

Problems:
	Creating a 6.295 MV MHD converter in reasonable space.
	
	Getting the alpha particle to hit our field instead of other 
	radioactives.
	
	Keeping the lamp in the right position so that it won't burn out
	and be inefficient. (No problem with incandescents, but they are
	*always* inefficient, nor with fluorescents (AFAIK) or LED lamps,
	but the latter is also quite inefficient, at least currently)
		Maybe do some sort of trick to skip the MHD and let the alpha
		particles ionize some gas directly. 
	
	Getting really light components for all this. I estimate we need some
	heavy shielding around the radioisotope+MHD to prevent someone from
	cracking it and breathing the resulting dust, something that would
	be Bad. It may make sense to have the thing as some sort of solid, 
	but then we hit problem #2.


If we use tritium (H-3), which can possibly be generated by fusion, we get 
around many of these problems. H-3 decays with beta (the best mode for direct 
conversion wrt inter-gas losses) into He-3  (itself valuable for fusion 
processes).
Furthermore, it has an energy of 0.54W/g after one half-life, and thus a
battery for light purposes would only require 55.4g to last the entire
period. The He-3/H-3 mix could be returned, separated and "refilled".
Finally, the decay energy is at only 19 KeV so insane voltages aren't required
for direct conversion.

The fusion process in question would be
	D + D = T + p + 4.03MeV (50%)
	      = He3 + n + 3.27 MeV (50%)
	
	(and if the side purpose is to evolve He3:
		Li6 + p = He4 + He3 + 4.0 MeV )

For a "millenial battery" we have Ra-226 at 0.029W/g (0.014 after 1600 years).
Ra-226 is easily accessible. (We don't get away from the alpha radiation
interaction problem though, as it is not a gas)