Here is a big one for you engineering fans to chew on.

First off, a little context:

The giant robot in question is called Mazinger Z, considered to be fiction's first pilotable mecha, launching the super robot genre.

Now while it's a bit of an engineering joke how implausible giant robots are, the creator of this work, Go Nagai, wanted to have some realism in presenting how a giant mecha would work, from difficulty of operation, multiple upgrades, it's lumbering movements, ect... see here for more

Even the power source was relatively realistic when first introduced. It was simply what happens when a special element undergoes nuclear fission: a large amount of photons and it gives off no pollution. See link here

Why do I call this relatively realistic? Look at this linked concept.
The thing about photonic rockets is that they require a ridiculous amount of energy to convert mass into photons, something that isn't an issue for Mazinger apparently.

Here is something a friend said when we were discussing this

in the first episode of the 70's anime Dr. Kabuto [the robot's creator] demonstrates the power of photons by firing some sort of electric bolt at a block of Japanium (the basis for photon power and Alloy-Z as well as its variants) This releases a huge mass of light, I'm assuming the supposed photons.

This light could be one of two things; one being a waste product like how the Cherenkov effect in nuclear reactors causes them to glow blue but doesn't aid in generating electricity. The other, less likely but still feasible, being that the photons released are harvested via the photovoltaic effect, meaning that Mazinger Z is technically solar powered in the same way that most nuclear reactors are technically steam generators.

The solar power solution definitely makes more sense, as it goes in line with the "100% clean" qualifier, but Dr. Kabuto would have had to invent technology far more advanced than our own in order to make solar cells than are that efficient. I don't think we even have solar cells today that work this well, and old man Kabuto is working with 70's technology.

This gave me more to think about...researching I came across Photon-intermediate direct energy conversion.

It sounds very similar to what my friend described...it is also interesting because as some research on the subject has stated

In addition to electric power, photolysis makes other product forms possible. These products include useful feedstock or combustion chemicals, such as hydrogen and carbon monoxide, and excited molecular and atomic states, used for laser amplifiers or oscillators.

This is really interesting as this reminds me of some of Mazinger's weapons, making me think that the robot is a walking weaponized reactor :)

But what do you think? Is any of this plausable? Is Japanium even remotely realistic? (I doubt it honestly, I mean no radiation?) Is PIDEC a plausable real world counterpart?

  • 3
    $\begingroup$ Minus all the fluff, are you just asking if you could use PIDEC to power a giant mecha? $\endgroup$ Oct 19, 2019 at 15:38
  • $\begingroup$ I find it interesting that articles going back to 1980's on PIDEC are still behind a paywall - there must be an incentive for that. What would make ultraviolet more efficient to convert to electricity than heat would be I wonder. </curiosity> $\endgroup$ Oct 19, 2019 at 15:50
  • $\begingroup$ @011358smell promises of higher efficiency would be enough if they panned out... talk of 70% combined PIDEC and thermal bottoming cycle. You could use the same trick for getting more energy out of D-T fusion, too. $\endgroup$ Oct 19, 2019 at 16:11
  • 1
    $\begingroup$ The power source you mention is not realistic. It says so in the link you provided it is a fictional power source. $\endgroup$
    – Slarty
    Oct 19, 2019 at 18:09
  • 1
    $\begingroup$ You would have to drastically shorten this question, OP. thanks! $\endgroup$
    – Fattie
    Oct 19, 2019 at 20:16

2 Answers 2


Lets just start with the Japanium question. Is there some magical element which would release energy only in the form of visible light photons? Well, maybe.

Nuclear isomers are excited states of regular atomic nuclei that can relax back to their ground state by the emission of a gamma ray. Now, not all gamma rays are created equal... it is basically a name given to a photon released by activity in an atomic nucleus, and usually that means it will be quite high energy, and as a result you'll get short wavelength and dangerous radiation of the sort people usually associated with the name "gamma ray".

Not all gamma rays have to be short wavelength. There is a nuclear isomer of Thorium, 229mTh, which releases a 7.5eV gamma ray. Most gamma rays have energies measured in tens or hundreds of kilovolts, but a 7.5eV photon has a wavelength of 165nm, which is juuuust into the UV range. Very tame for a "gamma ray".

Lets imaging that Japanium was a metastable nuclear isomer with a long half life and a ground state energy only a little below the excited state. Let us imagine further that you induce gamma emission in it by firing an electron beam at it, causing it to relax to its ground state and release a UV photon. Would that be useful as a battery?

Thorium 229m would of course weigh about 229g per mole, and that mole of thorium would have ~6x1023 atoms in it, and each one would release a 7.5eV photon. 1eV is about 1.6x10-19 joules, so this mole could release a little over 96kJ of UV light. Assuming you could reliably induce this gkind of gamma emission (which we can't, right now, and it may not be possible) and you can do it with relatively little investment of energy, and you could capture 100% of the emitted photons, you'd have an energy density of ~421kJ/kg. Turns out that isn't actually as high as the energy density achievable by modern Li-ion batteries.

And that's what happens when you want everything to be lovely and safe and clean. If you'd accept emission of nasty dangerous high energy, short-wavelength gamma rays, might be able to get something that's a million times more potent... and yet still has an energy density some thousand times less than a decent fission fuel. Oh well.

Is PIDEC a plausable real world counterpart?

PIDEC requires serious high-energy radiation first, which rather ruins the whole premise of Japanium. If you're happy to have high-energy dangerous radiation coming out of your power plant, then you could indeed theoretically build a nuclear powerplant using PIDEC and then do silly things with that power plant, like building a giant killer robot.

this reminds me of some of Mazinger's weapons, making me think that the robot is a walking weaponized reactor

Nuclear reactor lasers are, in fact, a thing that has been researched. They appear to work, and they could be jolly powerful.

The problem is that their power density is very, very low. Sure, you can get a continuous megawatt beam of doom, but you need hundreds of tonnes of reactor to do it.

You could handwave this away with a suitably powerful scifi reactor (of the sort a walking giant killer robot would probably need) that produces lots of high energy radiation (of the sort that PIDEC would need). Remember that you can't use the reactor to drive a laser and drive other things via PIDEC at the same time, though.

  • $\begingroup$ So basically, this would release gamma rays? "Nuclear reactor lasers are, in fact, a thing that has been researched. They appear to work, and they could be jolly powerful." If you think that's insane, look at it's other weapons. $\endgroup$ Oct 20, 2019 at 17:07
  • $\begingroup$ Rust Hurricane The powerful turbines in Mazinger Z's head create gale-force winds, launching them through the mouth grill. The attack includes highly corrosive particles (thought to be ionized hydrogen), almost instantaneously causing an enemy to rust over and fall apart. Breast Fire The large red fins on Mazinger Z's chest act as heat sinks for its Photonic Energy reactor. Mazinger Z can fire off this stored thermal energy as a powerful, 30,000 degree white-hot beam that melts almost anything. $\endgroup$ Oct 20, 2019 at 17:11
  • $\begingroup$ @JacobBlaustein my point was twofold... one that a material that can emit gamma rays is a good source of energy, and two that "gamma ray" can be used to mean longer-wavelength light, not just dangerous short wavelength radiation, but the weaker kinds of gamma ray make for poor energy sources. $\endgroup$ Oct 20, 2019 at 18:02
  • $\begingroup$ So you are referring to long wave gamma days? $\endgroup$ Oct 21, 2019 at 6:52
  • $\begingroup$ @JacobBlaustein yes, that is exactly what I talked about in my answer. $\endgroup$ Oct 21, 2019 at 8:34

Okay, I'm going to piggyback off Starfish Prime's answer here.

Japanium could be a nuclear isomer of some description. (A nuclear isomer is where the particles in the nucleus are above their ground state, and in particular we want isomers where this can last for more than, say, several hours.)

But, for it to be a no-pollution setup, the ground state that this energized isomer decays to must be a stable setup. For example, 180mTa, which has a half-life greater than the current age of the universe, decays into 180Ta. That decays via beta decay into other elements, meaning that once used the "Japanium" would have to be discarded like any other nuclear waste.

Let's give the show that, though, and move on. So now you've got a stable isotope that you need to be able to turn back into that nearly-stable isomer. A isomer is a battery, not a source of perpetual energy. Otherwise they might as well use whatever's powering that spark plug.

99mTe is usually made from Molybdenum-99, not 99Te, even though the ground state is long-lived enough that at attempt at recovery might be possible. (I'm using technetium-99m because it's really common because of how it's used in medicine.) And Mo-99 is made in nuclear reactors as a byproduct, effectively, meaning that there's nuclear waste from that step. Whatever is producing nuclear-reaction-energy particles to recharge the isomer is probably going to be using nuclear reactions, and means it generates waste.

Not to mention mining and refining all the material needed for this, too.

So, as far as the legendary no-pollution mecha reactor goes, the explanation doesn't hold water once you start to investigate.

  • $\begingroup$ Figures. Thanks anyways $\endgroup$ Nov 23, 2019 at 7:06

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