There is a nice table that shows, that Americium-241 has low power density, but it's half-life is 432 years. It also mentions that the real reason, why this is interesting, is because Am-241 is a byproduct and a pure isotope that can be used without refining.
> power density is inversely proportional to half-life
It's not that simple. The energy per event varies by orders of magnitude depending on the specific transition (even within given particle decays, the energy of the emitted particle varies), also the number of atoms per volume or mass varies depending on material.
Clearly. However it IS a good approximation. For RTGs, we desire primarily alpha emitters as alpha particles are generally the easiest type of decay product to shield (the thin metal casing will stop all alpha particles). And common Alpha emitters such as Po-210, Am-241, Pu-238, and U-232 all have a decay energy of about 5-6MeV even though they differ in half life (and thus power density) by 3 orders of magnitude.
The approximation holds true for the heavy elements, with similar atomic mass. I wonder if the power density of any similar half-life lighter nuclei would be significantly greater, or whether the energy of decay reduces roughly proportionately with their mass.
It has to first be separated from the rest of the actinide waste, which is very challenging, as they're chemically similar elements. Previously this had to be done with a centrifuge (separating by mass), but a lot of research effort has gone into developing more practical chemical refining methods.
A lot of newer smoke detectors work on a photo-electric principle rather than by ionisation. That means they don't contain anything radioactive, and also tend to be more effective because they're less prone to false alarms.
Flame detectors work via video feeds typically and analyze a video for flame and smoke patterns. Those come in both stand alone detectors and systems that work off of existing security camera feeds. (see also UV based detection)
They were referring to a photoelectric smoke detector vs ionization types. Both are still available but photo is much more common now days. They look exactly the same exterior wise, but it works by having a tiny light box where smoke goes in and changes the light the sensor is seeing. They can still cause false alarms because they are sensitive to dust and particulate matter, but they operate on intelligent addressable systems now which can adjust their sensitivity to some degree over time.
So is this essentially an RTG powered by Americium instead of Strontium or Plutonium? Or is this pioneering a new method of operation compared to a traditional RTG?
I don't think the power generation part of this is a breakthrough at all, just a "proof of the pudding is in the eating" demonstration.
As I understand it, the practical refinement of a significant amount of Americium from waste is the breakthrough. But that doesn't win hearts and minds like a 432 year space lightbulb.
> So is this essentially an RTG powered by Americium instead of Strontium or Plutonium?
That is the idea. Plutonium RTGs are very hard to get by. As in only the U.S. have a few such RTGs in stock and I am not sure they are producing new ones.
I cannot express how disappointed I was to learn that they are just using the americium as a heat source, and not converting the kinetic energy of the alpha particles directly to electric current by induction.
These (Americium RTGs) work pretty good in Minecraft (specifically Enigmatica 2 Expert Mode). Reliable, decent power output, zero maintenance. Not got as far as orbit yet, but I expect to take at least one of these with me to power the spacecraft.
There is a nice table that shows, that Americium-241 has low power density, but it's half-life is 432 years. It also mentions that the real reason, why this is interesting, is because Am-241 is a byproduct and a pure isotope that can be used without refining.