Death Rays and Disintegrators

Sometimes they were called "blasters, ray guns, or even zap guns," although that last one was sometimes also used for the "stun gun" the puny sibling to the much mightier Death Ray. Asimov had one called a "Disinto." Hugo Gernsback was sure they’d be either radio waves or powered by radium. Fritz Leiber imagined the "fission pistol," that had all the nuclear reactions in the gun going in the same direction. A. E. van Vogt used light to "conduct" nuclear reactions to the target, at least on the Space Beagle. In Slan, it was just raw atomic power. Once in a while the death rays were "sonic." More frequently they were "electron guns" which actually exist in television sets, but for something else entirely (though one may argue that TV is something of a stun device). H. G. Wells began the whole thing with the "heat ray."

And we wanted them, maybe as much as we wanted to go into space (which is maybe why I wasn’t as interested in the things as my fan boy brethren). And it wasn’t just us. During WWII, the U.S. Army's Aberdeen Proving Ground offered a standing reward to anyone who could demonstrate a death ray capable of killing a tethered goat. Britain's Air Ministry put up a similar prize to the inventor whose ray could kill a sheep at a range of a hundred yards. There’s a story that radar was invented partly because of a 1934 rumor that Germany had invented a microwave-based death ray.

Because hell, nobody messes with you if you’re packing a Death Ray.

So when lasers were announced in 1960, and we all heard that one could punch a hole in a diamond, or a metal plate, well, in a lot of manuscripts the word "blaster" got crossed out and "laser" got inserted.

Trouble was, they didn’t work like that. They were made of light.

Remember all those tales about the magic spell that is deflected by the mirror? Well, dang, you could do that to a laser, it turned out. Also, fog, smoke, not so good.

Moreover, they were damned inefficient. You had to put in kilojoules to get out joules. Later, some of them got more efficient, and some, like the CO2 laser, could be pumped by chemical reaction. I read about a 4000 watt laser in the late 1960s, from Raytheon, as I recall. It was powered by a gas turbine, basically a jet aircraft engine, and it was chemically pumped. But notice, a jet engine to pump a laser that has the output of—a couple of hair driers. (I’m talking continuous power here, the pulsed ones can put out more power than the whole U.S. power grid—for a picosecond).

CO2 lasers can get up to pretty high efficiencies these days, about 20% and some of them are upwards of a hundred kilowatts. But consider, to get water from room temperature (about 20 degrees C) to boiling, you need top put about 330 kilojoules into it for every kilogram (about a half gallon). The heat of vaporization of water is about 2260 kilojoules per kilogram. So to boil a half gallon of water, you need around 2600 kilojoules. It takes even a 500 kilowatt laser 5 seconds to boil a half gallon of water.

You're also boiling four times that much water in your cooling system, incidentally.

Yeah, it’ll hurt you plenty quick if you stick your hand in a laser beam that powerful, but we’re sure not in disintegrator ray territory. Not by a long shot. Was James Bond about to get his testicles cut off and be severed in two? Probably not; the thing would have set his clothing on fire, though.

So the "laser death ray" future turns out to be one that dated faster than just about any other sci-fi gimmick ever. Still, the "phaser" was a brilliant neologism. It took the "-aser" suffix, which still has some mysterioso power, even now, and added, well, what? More mysterioso. Something to do with "phase" probably. So soon it was "phaser" and "plasma rifle" and "hypervelocity rail gun," as everyone took a quick swing back into fantasy land, which is what Space Opera is all about anyway. Nobody took the Laser Death Ray seriously after that.

Except, it turns out, for the Department of Defense. I think they’re still pushing space-based laser missile defense systems. These have the positive aspect of being largely harmless hogwash, good for tech pork and not much else. Physicists still love them some laser macho, and between the space lasers and attempts to use lasers to light fusion reactions, they get to keep playing, I’ve Got the Big One.

Dr. Evil: You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads! Now evidently my cycloptic colleague informs me that that cannot be done. Ah, would you remind me what I pay you people for, honestly? Throw me a bone here! What do we have?

Then there is the saga of the Gamma Laser or X-ray Laser, but I’ve already written about that one.

And then there’s the one about using an ultraviolet laser to conduct a taser current (there’s that –aser mojo again). Look ma! We have a stun gun!

Too bad all you have to do is wear a wetsuit or a rubber raincoat to be immune. There’s a reason why real tasers have little sharp barbs at the end.

The Gamma Laser

Originally written July 27, 2006

I saw Sharon Weinberger on the Daily Show, last night, touting her book, Imaginary Weapons. The book is her expose of weird DOD projects involving fringe science, etc. Amid the talk about psychic espionage and mind control rays, she mentioned the “atomic hand grenade” and hafnium. I know a lot of the background of that one, so there’s an excuse.

In the early 60s, when I was barely a teenager, there was an article in Scientific American about the gamma ray laser, graser, gaser, call it what you will. I read the article, talked about it with my science buddies, then put it in the back of my mind for a while. Then I went to RPI and joined the Rensselaer Engineer, the school’s student engineering magazine, and wrote a lot of articles, so many that some had to be under pseudonyms. One of them was on the gamma laser.

RPI’s library at the time was under fire for being inadequate, but it was good enough to get me a copy of the paper by Lev Rivlin describing the gamma laser, and I was young and cocky and indulged in a bit of speculation of my own in the article. So let me give some technical background.

Lasers work by a quantum trick. Light is typically emitted from an atom that is in an “excited state,” i.e. one or more of its electrons is not in its lowest possible energy level. The situation is symmetric, in that an atom in its lowest energy state (the ground state) will also absorb a photon to put it up into the excited state. The probability of the atom emitting a photon is related (actually, with caveats, it’s identical) to its likelihood of absorbing the photon in the reverse reaction.

It turns out (this was an Einstein thing), that you can get the atom to emit its photon “prematurely” if you hit it with a photon of exactly the same energy as the one it will emit. Thus the “stimulated” part of the light amplification through stimulated emission of radiation, and since you now have two identical photons, you also get the “amplification.”

In order to get real amplification, you need what is called an “inverted population,” where the number of atoms in the excited state is greater than the number of atoms in the ground state, otherwise the ground state atoms absorb all the photons you can make. Inversion is usually done by “pumping” the ground state into much higher energy states, which then decay into a “metastable state,” one that hangs around for a much longer time. Pumping can be done optically, chemically, or electrically, and all three are used in lasers.

The gamma ray laser does all this with energy shells in the atomic nucleus rather than electrons in the outer atomic shell. Also, because gamma rays are more energetic than regular light, you get a problem called “dynamic line broadening.” What happens there is that, because gamma rays pack a lot of energy, they have a “kick” that causes the emitting nucleus to recoil. But that recoil lowers the energy of the emitted photon, so it’s no longer at the right energy to stimulate the emission of the next atom. So the lasing action becomes very inefficient.

What Rivlin proposed was to make use of the Mossbauer effect. In the ME, the atom is embedded in a crystal matrix, and said crystal matrix allows the atom to vibrate only at certain fixed energies, so-called “phonon resonances.” That’s another quantum effect. If the “kick” from the gamma emission doesn’t match one of these resonances, then the entire crystal matrix is what rebounds. Well, the difference in masses between a macrocystal and a single atom is so great that all the energy goes into the photon and essentially none is lost to the matrix.

That left two problems for the gamma laser. The first is how to get the inverted population. The second is how to make an “infinite medium” i.e. get a long enough path in the lasing medium to obtain a lot of amplification. In most lasers, you put mirrors at both ends to create a “long path,” for the photons and lasing medium to do their thing.

Rivlin suggested that with a properly metastable isotope of high purity, only a few centimeters would constitute an effectively long path and no mirrors would be necessary. Others have suggested specially created crystal diffraction mirrors (which can reflect even low energy gamma rays if they are properly tuned to the correct frequency). In my little article, I suggested that low angel reflection might be sufficient, so you’d have maybe dozens of rods arranged in a polygon, each only a couple of degrees off the next, with a low angle metal surface in between. A similar trick is used for x-ray astronomy.

Pumping was something else again. I don’t think that either Rivlin or the Scientific American article suggested nuclear transmutation via neutrons, but that was something that I also speculated about.

Nothing much happened on the nuclear laser for another decade or more, but it became a hot topic for a little while during the SDI (“Star Wars”) period. There was even an underground bomb test that was briefly touted as having achieved amplification. Later that result was said to be a measurement error by some, while others hinted darkly at fraud. It appeared like the design was an attempt to “brute force” the matter (and there’s no brute like a thermonuclear bomb), but I could never figure out how they were going to solve the line broadening problem, and, by all reports, they didn’t.

In 1987 there was an experiment reported involving a metastable isotope of tantalum (Ta180m) exposed to high energy x-rays, with the result being a fluorescence that seemed to indicate some quantum stimulation was occurring. For a variety of practical and theoretical reasons, a lot of attention was then given to hafnium-178m2, the second metastable isotope of hafnium, having a half-life of about 30 years.

In 1999, a University of Texas group announced a stimulated emission result from hf178m2, triggered by a dental x-ray machine. It seemed like the Holy Grail was coming into view.
But then the criticisms began, the worst of which being that no researcher has ever replicated the original result, not even one of the UT group. Also, the original experiment did not have a control, so WTF?

Then came theoretical calculations that said that the process shouldn’t have actually reached breakeven, but a practical consideration was more important. The isotope does not occur in nature and is the product of an accelerator, which makes it hugely expensive. The idea of making a weapon out of it is ludicrous.

Well, so much for that.

But, as I say, I follow the field generally, and there is another story out in the hinterlands:

United States Patent 4,939,742 Bowman July 3, 1990 Neutron-driven gamma-ray laser

Abstract
A lasing cylinder emits laser radiation at a gamma-ray wavelength of 0.87 .ANG. when subjected to an intense neutron flux of about 400 eV neutrons. A 250 .ANG. thick layer of Be is provided between two layers of 100 .ANG. thick layer of .sup.57 Co and these layers are supported on a foil substrate. The coated foil is coiled to form the lasing cylinder. Under the neutron flux .sup.57 Co becomes .sup.58 Co by neutron absorption. The .sup.58 Co then decays to .sup.57 Fe by 1.6 MeV proton emission. .sup.57 Fe then transitions by mesne decay to a population inversion for lasing action at 14.4 keV. Recoil from the proton emission separates the .sup.57 Fe from the .sup.57 Co and into the Be, where Mossbauer emission occurs at a gamma-ray wavelength.

This if very similar to some of the speculations I had back in 1969, but it gets around a big problem I noticed. I thought that the target nucleus would have to be of low atomic weight (low z) because otherwise the Compton effect would be too parasitic to allow amplification. This patent suggests that the production of the excited nucleus can be made to eject the atom from its normal substrate into a medium (in this case, beryllium foil) that is very low z, where the actual lasing would occur. I was thinking thermal neutrons, but the patent uses higher energy neutrons, so that’s how the recoil would occur. I also suspect that there may be some small angle gamma/x-ray reflection occurring in the device as well.

The patent holder, Charles Bowman, is someone I’ve noticed before; he was on of he scientists analyzing the Yucca Mountain nuclear waste site and who described a scenario where there might be a (low yield) nuclear explosion from the nuclear waste. That particular bit of work fit in with some other speculations that I’ve had, about highly moderated nuclear supercritical reactions, something that’s about half-way between a so-called “dirty bomb” and a real nuke. But that’s a topic for another time.

SDI

A buddy of mine from the air biz used to work at Lawrence Livermore Labs, and he was once at a luncheon where Edward Teller was holding forth. Since there were several atmospheric scientists at that particular lunch, at one point Teller speculated on whether it would be possible to set up a series of nuclear explosions that would cause atmospheric particulates to precipitate out of the air.

My friend was a little nonplussed, because this was a truly loony idea. But after thinking about it for a while, he chalked it up to Teller having a little fun with his own reputation. He had, after all, basically invented the thermonuclear bomb, and had then spent much of his remaining career overseeing its refinement, and looking for some place to use it. From proposed massive canal building projects to attempts to get more natural gas out of geological formations, Teller always had that single tool that he was trying to use: the H-bomb.

Later, when we all heard about the Teller’s backing of the Strategic Defense Initiative (called “Star Wars” in the popular press), some of us immediately wondered, “Where’s the bomb?”

We learned soon enough about the proposed X-ray (or gamma ray) laser, which was supposed to be pumped by a thermonuclear explosion, so there you are and bob’s your uncle. As I've noted in another essay, I didn’t expect that to work, for technical reasons, and it didn’t.

SDI did not die with the gamma laser failure, however. We’ve had various debates about the feasibility of “hitting a bullet with a bullet” vs “smart rocks” or “brilliant pebbles,” (or “sentient sand” for all I know). In any case, there’s really no idea so lame that a DOD bureaucracy won’t champion it, but there are some things that generally don’t get said, so I’m going to say them here.

The fact is that there are certain paths of least resistance in engineering. Some ideas, no matter their soundness or unsoundness, will never happen, because something else that is technically easier will happen first. It’s important to know what it is that will happen first.

A ballistic missile’s brief career is divided into several important phases: launch, boost, ballistic, re-entry, target, then boom. There were actually some studies in the early 1970s, during the ABM (anti-ballistic missile) debate, that suggested that it might barely be possible to stop a single bomb in the near-target phase, using what is essentially massive anti-aircraft fire, putting a more or less continuous shroud of shrapnel as an umbrella near the target. No one really thought of this as a good solution, for several thousand reasons, including the fact that it would only work on one bomb, and an early trigger would then blow all your anti-aircraft weapons to hell and gone.

Similarly, despite the PR graphics of SDI as a “shield,” there was never much intention to try to get at ballistic weapons in the re-entry phase, not least being that a single thermonuclear explosion at the edge of the atmosphere creates a good sized EMP pulse that will then blind subsequent defense radar.

That argument also applies to defensive measures during the entire ballistic phase, when the warheads are outside of the atmosphere in free-fall. But there’s actually a worse problem in the ballistic phase, camouflage.

In the absence of an atmosphere, anything, no matter how lightweight, follows a ballistic trajectory. It is very easy, therefore, to create decoys, simple balloons with the same radar signature as the warhead. In fact, you can put a balloon around the warhead and make it look exactly like the balloon. Since the balloon/decoys weigh only a few ounces, you can put hundreds of them in the same ballistic trajectory as your warhead, turning the problem from “hitting a bullet with a bullet” to “shooting a needle in a haystack.”

So no one really expects to take out a warhead during the ballistic phase. That leaves us with launch and boost. Launch is over in a few seconds, so the real development work is on stopping missiles in the boost phase, when they are conveniently located far away from the target (us) and near the launch site (them).

But how? First you have to sense the launch, then find the missile, then target it, then put something near to it, then kill it. That implies a really good sensor network, plus the ability to put your kill vehicle near the target very quickly.

The sensor network is easy, or, more accurately, it’s so difficult that there’s really only one way to do it, and that must be space-based. You need orbiting infrared sensors to see the launch, then something akin to radar to track it. The radar will need to be close to the boost, and that too is almost necessarily space-based. There have been arguments about “pop up” systems, but those are mostly red herrings; it’s a lot easier to do it from space.

Likewise, it’s a lot easier to target a high velocity vehicle with something that starts off at high velocity. If your initial sensor is in space, and your radar net is in space, the same arguments tell you that your kill vehicle needs to be from space.

Along this development pathway, as your identification and tracking systems get better and better, there will come a time when only the most effective type of kill vehicle will work. You can talk all you want about “brilliant pebbles,” and “kinetic kill” vehicles, but nothing beats a nuke for destruction at a distance. At high altitudes, the energy from a nuclear weapon is primarily in the form of hard X-rays, with an attendant electromagnetic pulse. The hard X-rays can melt or crack a warhead by uneven heating, and a nuke doesn’t really care how many decoys you put up, it’s going to blow them all away. The electromagnetic pulse will probably even wreck any putative missile guidance system from a much greater range.

So let me be very blunt here. There’s nothing secret about any of this. It is the inevitable result of any feasibility analysis. SDI is about putting nuclear weapons in orbit. It always has been.