MuonRay: SILEX Process -Top Secret Laser Enrichment Process Revealed

Thursday, 9 May 2013

SILEX Process -Top Secret Laser Enrichment Process Revealed

Introduction to Laser Enrichment

Laser enrichment began in the mid-60’s for the purpose of separating isotopes of elements by the process of selective ionization by lasers. This process was designed to produce higher concentrations of specific desired isotopes of a chemical element by removing them from other isotopes that are not of use. The most popular and developed work has been performed on natural uranium. This process is a large contributor to the nuclear power industry and weapon development. Using the unique frequencies which atoms vibrate in gaseous form, a laser tuned to the vibrational frequency of a U-235 atom can cause the isotope to behave differently from the heavier U-238 atom to allow harvesting. However, technical difficulties have impeded translation from the laboratory to the commercial or weapons settings despite the efforts of more than a dozen countries since the 1970s.

Discovery

Laser enrichment was based around the early work coming from the 1970’s like MLIS (molecular laser isotope separation) and AVLIS (atomic vapor laser isotope separation). These two early discoveries in laser enrichment were both transferred into the United States Enrichment Corporation. The latter of the two earlier developments used tunable dye lasers which were able to make 235-Uranium absorb the photons and undergo excitation. The ions were then electostatically deflected into a collector while the unwanted was passed through. ^[1].

Different Elements

1.Uranium- Laser enrichment of uranium is the most common application of laser enrichment and will discussed in detail below. This process separates isotopes for use nuclear fuel and energy production, and is much more useful and space efficient than older methods of uranium enrichment.

2.Carbon- Laser enriched carbon has applications in development of semiconductor material and biomedicine. The enriched Carbon-12 is of use in semiconductors, and the bi-product of this enrichment, Carbon-13 already has known uses in the biomedical field.

3.Silicon- Laser enrichment of silicon can be used for creating advanced semiconductor material. Creating isotopically pure silicon may be of use in devices with semiconductors, which include all computers and electronic devices. These devices that use silicon in its current form are reaching performance limits, and may be able to benefit from enrichment of silicon, though there is little demand for this and no economically sound source has been developed.^[2]

Success of LANL of laser enrichment of different elements can be seen in the table below. The different types of Dissociation methods will be described below in the Analysis section.^[3]

Commercial Energy

General Electric (GE) currently plans to use the Australian laser enrichment technology (SILEX) to enrich natural UF6 gas in the uranium-235 isotope. GE is planning to conduct the project in two phases. The first, a test phase while the latter being a commercial-scale enrichment plant phase. The Test Loop, which is being built at GE's nuclear fuel fabrication facility in Wilmington, North Carolina, USA, will verify performance and reliability data for full scale (commercial-like) facilities^[4]. This change in energy source could prove to be a much cheaper way of energy production that would allow for the lowering of cost per unit of power.

Nuclear Weapons

Fuel for nuclear reactors does not come out of the ground ready to used. Rather, fuel suppliers must process natural uranium to extract small amounts of the rare fissile U-235 isotope to produce the fuel pellets that reactors use to generate power. Typically a power reactor will utilize fuel enriched with 3% U-235, a nuclear weapon 80-90%.

Over the decades efforts continued to develop more economical enrichment techniques for both civil and military purposes. Much research centered on laser enrichment.

The Nuclear Regulatory Commission staff contends that its current licensing suffices to deal with security questions, but APS responds that "nonproliferation is not given an adequate level of attention." It gets support from NRC chairman Gregory Jaczko who conceded in a July 12, 2010 speech that "the smaller footprint and lower energy needs of the laser enrichment technology have been the cause of concern."

While SILEX may still fail as a commercial venture, we must prepare ourselves for success and the renewed interest in laser enrichment it will stimulate globally. With construction of more of the SILEX plant looming, it is none to soon for the Agency to consider interfacing with NRC and GE-Hitachi to work out an arrangement to establish a new safeguard precedent. Clearly marginally tethered international laser development is something we must avoid to prevent yet more nuclear weapons states in the future.^[5].

Analysis of SILEX Process

The Separation of Isotopes by Laser Excitation, SILEX, process exposes a cold stream of a mixture of uranium hexafluoride (UF6) molecules and a carrier gas to energy from a pulsed laser. The laser used is a CO2 laser operating at a wavelength of 10.8 μm (micrometres) and optically amplified to 16 μm, which is in the infrared spectrum. The amplification is achieved in a Raman conversion cell, a large vessel filled with high-pressure para-hydrogen.

The 16 μm wavelength laser preferentially excites the 235UF6, creating a difference in the isotope ratios in a product stream, which is enriched in 235U, and a tailings stream, which has an increased fraction of the more common 238U. In effect, the laser is tuned to electrically charge the U235 atoms, which can become trapped in an electric field and drawn to a metal plate for collection.

According to John L. Lyman, the Silex Systems Ltd. (SSL) research facility in Australia uses a laser pulsed at a frequency of 50 Hz, a rate that results in great inefficiency. At 50 Hz, only 1% of the UF6 feedstock is processed. This results in a high fraction of feedstock entering the product stream and a low observed enrichment rates. Consequently, a working enrichment plant would have to substantially increase the laser duty cycle. In addition, the preparation time needed is prohibitively long for full-scale production. The SSL research facility requires ten hours of prep time for a one-hour enrichment test run, significantly restricting output.[11]
Further details of the technology, such as how it differs from the older molecular laser isotope separation(MLIS) and atomic vapor laser isotope separation (AVLIS) processes are not known publicly and this has been the greatest source of controversy.

How Laser Enrichment Works

SILEX uses laser radiation to break bonds and ionize elements to separate isotopes by means of selective ionization. For natural uranium in particular, the laser breaks one of the six Florine bonds in UF6 utilizing photo-dissociation to create UF5+ which contains the U-235. Photo-dissociation is a complex process and will be explained below in its own section, but all in all it uses photon interactions with the chemical bonds to break the bonds themselves. The lasers are specifically tuned to ionize U-235, and not U-238.

With the UF5+ which contains U-235 having a positive charge, the molecules can be separated from the UF6 which contains the U-238. The U-235 ions are attracted to and collected on a negatively charged plate. This process can produce samples of nitrogen that are 5% U-235, versus natural uranium which is only 0.7% U-235.^[6] Since the energy of a photon is given by the equation:

[7]

this shows that the energy is inversely proportional to the wavelength of the photon. Different isotopes have different electronic energies. The equation above shows that energy is a function of wavelength, meaning isotopes of different energies will respond to different color lasers, that have different wavelengths. ^[8]

Photo-dissociation

Photo excitation of atoms is nothing new. Stanislaw Mrozowski suggested that mercury isotopes might be separated by selective excitation with the 253.7-nanometer resonance line of a mercury arc lamp and subsequent reaction with oxygen. This separation was achieved experimentally by Kurt Zuber in 1935^[3] In the early 1940 Harold Urey proposed a photochemical method for separating Uranium isotopes but he lost out to the gaseous diffusion technique. After World War II Carbon and oxygen isotopes were also separated by using a strong spectral line of an iodine lamp to excite carbon monoxide molecules. "These pre-laser experiments involved a one step process in which absorbed photons with frequencies in the visible or ultraviolet spectral region to selectively excite electronic states of one isotopic species"^[3]They were however limited by most molecules having very broad structureless electronic absorptions bands thus making selective excitation by this method impossible and by the intensity of the radiation sources available. Photo-chemical isotope separation requires highly monochromatic, highly intense radiation. High-intensity tunable laser have removed many of the limitations of the early experiments. These laser can be tuned to match any absorption features that show a distinct isotope shift, and because of its high monochromaticity laser light can excite a desired species with reasonable selectivity even when absorption feature of other isotopic species partially overlap those of the desired isotopic species. A high-intensity laser can also saturate the absorbing material as well. The best part though is that the laser pulses are short compared with the average time for the selectively excited molecules to lose their energies. Short pulses are needed if the excitation process is to be isotopically selective and efficient in its use of laser photons.

There are three methods of Photo-dissociation that have been used successfully. A single photon process where a visible or an ultraviolet photon excites a molecule to a "predissociative state". A two step process, in which an infrared photon excites a vibrational state of a molecule and an ultraviolet photon dissociates the excited molecule, and a multistep infrared process in which infrared photons excite successively higher and higher vibrational states until the molecule dissociation limit is reached. Every one of these processes take advantage that in a vibrational state the nuclei of a molecule undergo oscillatory motion about the ground state configuration at some frequency. This frequency depends on the masses of the nuclei thus the vibrational excitation of a molecule containing a lighter isotope requires absorption of a photon at a higher frequency. This mass dependent shift in the absorption spectrum is exploited to dissociate molecules of one isotopic species selectively to achieve isotope separation.

A single photon excitation relies on predissociation in which a photon induced transition from a bound ground electronic state to an electronic state for which the internuclear forces are always repulsive. The lifetime of such a repulsive state is so short that dissociation follows the transition to the excited state is almost unity probability.

Predissocitation involves a photon-induced transition not directly to a repulsive electronic state but to a predissociative state (a vibrational state within a bound excited electronic state that is energetically coupled to the repulsive electronic state. That is the bound excited and repulsive electronic states have the same energy (the curve-crossing energy) at some internuclear distance greater than the equilibrium internuclear distance for the ground electronic state.) Then if the bound excited and repulsive electronic states have certain symmetry relations and if the energy of the vibrational state is near the curve-crossing energy, dissociation occurs by tunneling from the bound excited electronic state to the repulsive electronic state. This dissociation by tunneling is called predissociation because it requires a photon energy less than that required for dissociation directly from the repulsive electronic state."^[3] Tuning a laser to the frequency matching the isotopic species transition energy that species can be selectively excited and dissociated. A requirement for isotopic selectivity of predissociation is that shift of the vibrational energy levels for the different isotopic species be greater than their energy widths.

Los Almos National laboratory has been experimenting using selective photo-dissociation of molecules. Molecules can be excited to dissociate in many different ways, and this is the two step process described above. The two main steps that Los Almos was as follows. The first one was the use of an infrared laser that selectively excites the vibrations of gaseous UF6 that contains the molecule of U-235. As you can see below in part (a) of the figure there is a difference in the energy to excite the vibrational modes of one isotope to another (the solid line is one isotope and the dash line is another isotope.

^[3]

The arrows in part (a) show the absorption of infrared photons that raise a molecule from the ground state to the first vibrational state. The difference in the lengths of the arrows show the different photon energies, or frequencies needed to excite the two isotopic species but the difference is quite small (less than 1.25X10^-4 eV). Monochromatic lasers can achieve selective excitation process though. Part (b) of the diagram shows one of the vibrational transitions in (a) that is split into many rotational states labeled by J (number of rotational angular momentum quanta of the states) At room temperatures molecules populate rotational states with high J values which causes a problem for the monochromatic laser as the laser is tune to excite the ground state to the first vibrational state. If the UF6 are at rotational states above the ground state they will not be excited to the vibrational state and thus you will be unable to dissociate these unexcited molecules. Part (b) also shows that during a transition between vibrational states the change in J is restricted to -1, 0, +1 and are denoted as P-, Q-, and R- Branch transitions respectively. You can see in part (c) of the figure above the infrared absorption bands of 235-UF6 and 238-UF6 from 620 to 630 cm^-1 including transition from the ground state to the first excited state of the V3 vibrational mode. The absorptions occur over a broad band of frequencies because molecules in the ground state occupy many rotational states (J) and the molecules in each rotational state can undergo P-, Q-, or R- branch transitions to the first excited vibrational state. As you can see in part (c) the absorption band of 235-UF6 is shifted to slightly higher frequencies relative to that of 238-UF6

An ultraviolet laser is then shot onto the vibrational excited UF6 to dissociate the molecule into UF5 plus a fluorine atom. which cause it to reach the repulsive potential dissocation limted as show in the figure below

Ideally the lower-frequency ultraviolet photons will not dissociate the unexcited molecules and the selectivity of the first step will be preserved. In this process the excitation and dissocation must occur on a time scale that is short compared to the lifetime of the vibrational state otherwise they can undergo collisions and lose their excited vibrational state. We can see the benefit of using the two step process to help improve the selectivity of the isotopes that undergo photo-dissociation by looking ultraviolet dissociation cross section for vibrational excited molecules and unexcited molecules as shown below

As you can see above the dissociation probability as a function of ultraviolet photon frequency of both the excited and unexcited states. Without infrared excitation the dissociation cross-section for different isotopic species are nearly the same. Infrared excitation increase the photo-dissociation cross section at a given frequency and shifts the threshold for dissociation to lower frequencies. This allows you to choose an ultraviolet laser frequency at which the dissociation cross section is large for excited molecules and small for unexcited molecules.

In multiple-photon dissociation they try to make the most of the fact that the threshold frequency for ultraviolet dissociation shifts more and more to the color red as the infrared laser fluence (flux integrated over time) increases. The figure blow shows the ultraviolet dissociation cross section spectrum for CF3I.

These shifts clearly show that the laser is exciting the molecules to very high vibrational states and if molecular vibrations were governed by forces that increased linearly with displacement as if they were a harmonic oscillator the energy difference between vibrational states would be constant and photons with this constant energy could resonantly induce transitions to higher and higher vibrational states. Part (a) in the next figure shows the excitation states

Unfortunately most molecular vibrations are anharmonic that is they have nonlinear forces. The anharmonicity cause the energy differences between vibrational states to become smaller and smaller as shown in the figure above in part (b). As the molecules vibrational energy increase it should absorb infrared photons of lower energy and its interacton with constant-energy photons becomes ineffective of exciting it to the next vibrational state. This is the cause of the multi-stage needed for multi-photon dissociation. A diagram of a proposed system for a multi-photon dissociation system for enriching Uranium enrichment of UF6 gas is shown below.

((All figures from this section was taken from source^[3]))

Improvements Over Past Techniques

To be of use in nuclear power uranium must be enriched to Uranium-235. The first enrichment process used was gaseous diffusion of uranium, which involves forcing gaseous uranium through porous membranes which essentially filters through U-235 because it is lighter and diffuses faster than U-238. In each successive chamber the concentration of U-235 to U-238 is slightly higher, but more than a thousand chambers are needed to increase the concentration of U-235 to 3.2% which is required for light water reactors. The next process to be developed, which was more cost effective and is now the main commercial process currently in use, involves the centrifuging of uranium. Gaseous uranium is placed in a centrifuge and the heavier isotope U-238 moves to the outside of the centrifuge and U-235 remains in the center. This process is repeated up to 20 times, which is much less than the 1000 stages used in the diffusion process.^[9] Using laser excitation, uranium can be enriched to 5% U-235 after only a few stages of the process, but the centrifugal process would require thousands of stages to achieve these results.

Public View and Concerns

The main worry in developing this technology is that laser enrichment is so space and energy effective, so that those using this technology could go undetected by nuclear inspectors. Experts from the Council on Foreign Relations worry that these facilities could be “hidden in a warehouse,”^[10] as the SILEX process is 75% smaller than current techniques. New facilities would not be able to be easily detected by current observation satellites. ^[11]

It is important to note that the risk of proliferation is always present with the emergence of new nuclear techniques, although precautions are of course taken by the US government and the UN to prevent the spread of new technologies.

Summary

Laser enrichments purpose of separating isotopes of elements by the process to produce higher concentrations of specific desired isotopes of a chemical element. This process has the potential to be large contributor to the nuclear power industry and weapon development. Using the unique frequencies which atoms vibrate, a laser tuned to the vibrational frequency of an atom allows for harvesting. Because of technical difficulties translation from the laboratory to the commercial or weapons settings despite the efforts of more than a dozen countries since the 1970s, have impeded further advancements.

References

Monday, 31 December 2012

Richard Feynman - There's Plenty of Room at the Bottom

An Invitation to Enter a New Field of Physics

Richard P. Feynman

This is a transcript of the classic talk that Richard Feynman gave on December 29th 1959 at the annual meeting of the American Physical Society at the California Institute of Technology (Caltech). This was first published in the February 1960 issue of Caltech's Engineering and Science, which owns the copyright.

Richard Feynman in 1959.

Introduction

I imagine experimental physicists must often look with envy at men like Kamerlingh Onnes, who discovered a field like low temperature superconductivity, which seems to be bottomless and in which one can go down and down. Such a man is then a leader and has some temporary monopoly in a scientific adventure. Percy Bridgman, in designing a way to obtain higher pressures, opened up another new field and was able to move into it and to lead us all along. The development of ever higher vacuum was a continuing development of the same kind.

I would like to describe a field, in which little has been done, but in which an enormous amount can be done in principle. This field is not quite the same as the others in that it will not tell us much of fundamental physics (in the sense of, “What are the strange particles?”) but it is more like solid-state physics in the sense that it might tell us much of great interest about the strange phenomena that occur in complex situations. Furthermore, a point that is most important is that it would have an enormous number of technical applications.

What I want to talk about is the problem of manipulating and controlling things on a small scale.

As soon as I mention this, people tell me about miniaturization, and how far it has progressed today. They tell me about electric motors that are the size of the nail on your small finger. And there is a device on the market, they tell me, by which you can write the Lord's Prayer on the head of a pin. But that's nothing; that's the most primitive, halting step in the direction I intend to discuss. It is a staggeringly small world that is below. In the year 2000, when they look back at this age, they will wonder why it was not until the year 1960 that anybody began seriously to move in this direction.

Why cannot we write the entire 24 volumes of the Encyclopedia Brittanica on the head of a pin?

Let's see what would be involved. The head of a pin is a sixteenth of an inch across. If you magnify it by 25,000 diameters, the area of the head of the pin is then equal to the area of all the pages of the Encyclopedia Brittanica. Therefore, all it is necessary to do is to reduce in size all the writing in the Encyclopaedia by 25,000 times. Is that possible? The resolving power of the eye is about 1/120 of an inch---that is roughly the diameter of one of the little dots on the fine half-tone reproductions in the Encyclopedia. This, when you demagnify it by 25,000 times, is still 80 angstroms in diameter---32 atoms across, in an ordinary metal. In other words, one of those dots still would contain in its area 1,000 atoms. So, each dot can easily be adjusted in size as required by the photoengraving, and there is no question that there is enough room on the head of a pin to put all of the Encyclopedia Brittanica.

Furthermore, it can be read if it is so written. Let's imagine that it is written in raised letters of metal; that is, where the black is in the Encyclopedia, we have raised letters of metal that are actually 1/25,000 of their ordinary size. How would we read it?

If we had something written in such a way, we could read it using techniques in common use today. (They will undoubtedly find a better way when we do actually have it written, but to make my point conservatively I shall just take techniques we know today.) We would press the metal into a plastic material and make a mold of it, then peel the plastic off very carefully, evaporate silica into the plastic to get a very thin film, then shadow it by evaporating gold at an angle against the silica so that all the little letters will appear clearly, dissolve the plastic away from the silica film, and then look through it with an electron microscope!

There is no question that if the thing were reduced by 25,000 times in the form of raised letters on the pin, it would be easy for us to read it today. Furthermore; there is no question that we would find it easy to make copies of the master; we would just need to press the same metal plate again into plastic and we would have another copy.

How do we write small?

The next question is: How do we write it? We have no standard technique to do this now. But let me argue that it is not as difficult as it first appears to be. We can reverse the lenses of the electron microscope in order to demagnify as well as magnify. A source of ions, sent through the microscope lenses in reverse, could be focused to a very small spot. We could write with that spot like we write in a TV cathode ray oscilloscope, by going across in lines, and having an adjustment which determines the amount of material which is going to be deposited as we scan in lines.

This method might be very slow because of space charge limitations. There will be more rapid methods. We could first make, perhaps by some photo process, a screen which has holes in it in the form of the letters. Then we would strike an arc behind the holes and draw metallic ions through the holes; then we could again use our system of lenses and make a small image in the form of ions, which would deposit the metal on the pin.

A simpler way might be this (though I am not sure it would work): We take light and, through an optical microscope running backwards, we focus it onto a very small photoelectric screen. Then electrons come away from the screen where the light is shining. These electrons are focused down in size by the electron microscope lenses to impinge directly upon the surface of the metal. Will such a beam etch away the metal if it is run long enough? I don't know. If it doesn't work for a metal surface, it must be possible to find some surface with which to coat the original pin so that, where the electrons bombard, a change is made which we could recognize later.

There is no intensity problem in these devices---not what you are used to in magnification, where you have to take a few electrons and spread them over a bigger and bigger screen; it is just the opposite. The light which we get from a page is concentrated onto a very small area so it is very intense. The few electrons which come from the photoelectric screen are demagnified down to a very tiny area so that, again, they are very intense. I don't know why this hasn't been done yet!

That's the Encyclopedia Brittanica on the head of a pin, but let's consider all the books in the world. The Library of Congress has approximately 9 million volumes; the British Museum Library has 5 million volumes; there are also 5 million volumes in the National Library in France. Undoubtedly there are duplications, so let us say that there are some 24 million volumes of interest in the world.

What would happen if I print all this down at the scale we have been discussing? How much space would it take? It would take, of course, the area of about a million pinheads because, instead of there being just the 24 volumes of the Encyclopaedia, there are 24 million volumes. The million pinheads can be put in a square of a thousand pins on a side, or an area of about 3 square yards. That is to say, the silica replica with the paper-thin backing of plastic, with which we have made the copies, with all this information, is on an area of approximately the size of 35 pages of the Encyclopaedia. That is about half as many pages as there are in this magazine. All of the information which all of mankind has every recorded in books can be carried around in a pamphlet in your hand---and not written in code, but a simple reproduction of the original pictures, engravings, and everything else on a small scale without loss of resolution.

What would our librarian at Caltech say, as she runs all over from one building to another, if I tell her that, ten years from now, all of the information that she is struggling to keep track of--- 120,000 volumes, stacked from the floor to the ceiling, drawers full of cards, storage rooms full of the older books---can be kept on just one library card! When the University of Brazil, for example, finds that their library is burned, we can send them a copy of every book in our library by striking off a copy from the master plate in a few hours and mailing it in an envelope no bigger or heavier than any other ordinary air mail letter.

Now, the name of this talk is “There is Plenty of Room at the Bottom”---not just “There is Room at the Bottom.” What I have demonstrated is that there is room---that you can decrease the size of things in a practical way. I now want to show that there is plenty of room. I will not now discuss how we are going to do it, but only what is possible in principle---in other words, what is possible according to the laws of physics. I am not inventing anti-gravity, which is possible someday only if the laws are not what we think. I am telling you what could be done if the laws are what we think; we are not doing it simply because we haven't yet gotten around to it.

Information on a small scale

Suppose that, instead of trying to reproduce the pictures and all the information directly in its present form, we write only the information content in a code of dots and dashes, or something like that, to represent the various letters. Each letter represents six or seven ``bits'' of information; that is, you need only about six or seven dots or dashes for each letter. Now, instead of writing everything, as I did before, on the surface of the head of a pin, I am going to use the interior of the material as well.

Let us represent a dot by a small spot of one metal, the next dash, by an adjacent spot of another metal, and so on. Suppose, to be conservative, that a bit of information is going to require a little cube of atoms 5 times 5 times 5---that is 125 atoms. Perhaps we need a hundred and some odd atoms to make sure that the information is not lost through diffusion, or through some other process.

I have estimated how many letters there are in the Encyclopaedia, and I have assumed that each of my 24 million books is as big as an Encyclopaedia volume, and have calculated, then, how many bits of information there are (10^15). For each bit I allow 100 atoms. And it turns out that all of the information that man has carefully accumulated in all the books in the world can be written in this form in a cube of material one two-hundredth of an inch wide--- which is the barest piece of dust that can be made out by the human eye. So there is plenty of room at the bottom! Don't tell me about microfilm!

This fact---that enormous amounts of information can be carried in an exceedingly small space---is, of course, well known to the biologists, and resolves the mystery which existed before we understood all this clearly, of how it could be that, in the tiniest cell, all of the information for the organization of a complex creature such as ourselves can be stored. All this information---whether we have brown eyes, or whether we think at all, or that in the embryo the jawbone should first develop with a little hole in the side so that later a nerve can grow through it---all this information is contained in a very tiny fraction of the cell in the form of long-chain DNA molecules in which approximately 50 atoms are used for one bit of information about the cell.

Better electron microscopes

If I have written in a code, with 5 times 5 times 5 atoms to a bit, the question is: How could I read it today? The electron microscope is not quite good enough, with the greatest care and effort, it can only resolve about 10 angstroms. I would like to try and impress upon you while I am talking about all of these things on a small scale, the importance of improving the electron microscope by a hundred times. It is not impossible; it is not against the laws of diffraction of the electron. The wave length of the electron in such a microscope is only 1/20 of an angstrom. So it should be possible to see the individual atoms. What good would it be to see individual atoms distinctly?

We have friends in other fields---in biology, for instance. We physicists often look at them and say, “You know the reason you fellows are making so little progress?'” (Actually I don't know any field where they are making more rapid progress than they are in biology today.) ``You should use more mathematics, like we do.'' They could answer us---but they're polite, so I'll answer for them: “What you should do in order for us to make more rapid progress is to make the electron microscope 100 times better.'”

What are the most central and fundamental problems of biology today? They are questions like: What is the sequence of bases in the DNA? What happens when you have a mutation? How is the base order in the DNA connected to the order of amino acids in the protein? What is the structure of the RNA; is it single-chain or double-chain, and how is it related in its order of bases to the DNA? What is the organization of the microsomes? How are proteins synthesized? Where does the RNA go? How does it sit? Where do the proteins sit? Where do the amino acids go in? In photosynthesis, where is the chlorophyll; how is it arranged; where are the carotenoids involved in this thing? What is the system of the conversion of light into chemical energy?

It is very easy to answer many of these fundamental biological questions; you just look at the thing! You will see the order of bases in the chain; you will see the structure of the microsome. Unfortunately, the present microscope sees at a scale which is just a bit too crude. Make the microscope one hundred times more powerful, and many problems of biology would be made very much easier. I exaggerate, of course, but the biologists would surely be very thankful to you---and they would prefer that to the criticism that they should use more mathematics.

The theory of chemical processes today is based on theoretical physics. In this sense, physics supplies the foundation of chemistry. But chemistry also has analysis. If you have a strange substance and you want to know what it is, you go through a long and complicated process of chemical analysis. You can analyze almost anything today, so I am a little late with my idea. But if the physicists wanted to, they could also dig under the chemists in the problem of chemical analysis. It would be very easy to make an analysis of any complicated chemical substance; all one would have to do would be to look at it and see where the atoms are. The only trouble is that the electron microscope is one hundred times too poor. (Later, I would like to ask the question: Can the physicists do something about the third problem of chemistry---namely, synthesis? Is there a physical way to synthesize any chemical substance?

The reason the electron microscope is so poor is that the f- value of the lenses is only 1 part to 1,000; you don't have a big enough numerical aperture. And I know that there are theorems which prove that it is impossible, with axially symmetrical stationary field lenses, to produce an f-value any bigger than so and so; and therefore the resolving power at the present time is at its theoretical maximum. But in every theorem there are assumptions. Why must the field be symmetrical? I put this out as a challenge: Is there no way to make the electron microscope more powerful?

The marvellous biological system

The biological example of writing information on a small scale has inspired me to think of something that should be possible. Biology is not simply writing information; it is doing something about it. A biological system can be exceedingly small. Many of the cells are very tiny, but they are very active; they manufacture various substances; they walk around; they wiggle; and they do all kinds of marvellous things---all on a very small scale. Also, they store information. Consider the possibility that we too can make a thing very small which does what we want---that we can manufacture an object that manoeuvres at that level!

There may even be an economic point to this business of making things very small. Let me remind you of some of the problems of computing machines. In computers we have to store an enormous amount of information. The kind of writing that I was mentioning before, in which I had everything down as a distribution of metal, is permanent. Much more interesting to a computer is a way of writing, erasing, and writing something else. (This is usually because we don't want to waste the material on which we have just written. Yet if we could write it in a very small space, it wouldn't make any difference; it could just be thrown away after it was read. It doesn't cost very much for the material).

Miniaturizing the computer

I don't know how to do this on a small scale in a practical way, but I do know that computing machines are very large; they fill rooms. Why can't we make them very small, make them of little wires, little elements---and by little, I mean little. For instance, the wires should be 10 or 100 atoms in diameter, and the circuits should be a few thousand angstroms across. Everybody who has analyzed the logical theory of computers has come to the conclusion that the possibilities of computers are very interesting---if they could be made to be more complicated by several orders of magnitude. If they had millions of times as many elements, they could make judgments. They would have time to calculate what is the best way to make the calculation that they are about to make. They could select the method of analysis which, from their experience, is better than the one that we would give to them. And in many other ways, they would have new qualitative features.

If I look at your face I immediately recognize that I have seen it before. (Actually, my friends will say I have chosen an unfortunate example here for the subject of this illustration. At least I recognize that it is a man and not an apple.) Yet there is no machine which, with that speed, can take a picture of a face and say even that it is a man; and much less that it is the same man that you showed it before---unless it is exactly the same picture. If the face is changed; if I am closer to the face; if I am further from the face; if the light changes---I recognize it anyway. Now, this little computer I carry in my head is easily able to do that. The computers that we build are not able to do that. The number of elements in this bone box of mine are enormously greater than the number of elements in our “wonderful'” computers. But our mechanical computers are too big; the elements in this box are microscopic. I want to make some that are submicroscopic.

If we wanted to make a computer that had all these marvellous extra qualitative abilities, we would have to make it, perhaps, the size of the Pentagon. This has several disadvantages. First, it requires too much material; there may not be enough germanium in the world for all the transistors which would have to be put into this enormous thing. There is also the problem of heat generation and power consumption; TVA would be needed to run the computer. But an even more practical difficulty is that the computer would be limited to a certain speed. Because of its large size, there is finite time required to get the information from one place to another. The information cannot go any faster than the speed of light---so, ultimately, when our computers get faster and faster and more and more elaborate, we will have to make them smaller and smaller.

But there is plenty of room to make them smaller. There is nothing that I can see in the physical laws that says the computer elements cannot be made enormously smaller than they are now. In fact, there may be certain advantages.

Miniaturization by evaporation

How can we make such a device? What kind of manufacturing processes would we use? One possibility we might consider, since we have talked about writing by putting atoms down in a certain arrangement, would be to evaporate the material, then evaporate the insulator next to it. Then, for the next layer, evaporate another position of a wire, another insulator, and so on. So, you simply evaporate until you have a block of stuff which has the elements--- coils and condensers, transistors and so on---of exceedingly fine dimensions.

But I would like to discuss, just for amusement, that there are other possibilities. Why can't we manufacture these small computers somewhat like we manufacture the big ones? Why can't we drill holes, cut things, solder things, stamp things out, mold different shapes all at an infinitesimal level? What are the limitations as to how small a thing has to be before you can no longer mold it? How many times when you are working on something frustratingly tiny like your wife's wrist watch, have you said to yourself, ``If I could only train an ant to do this!'' What I would like to suggest is the possibility of training an ant to train a mite to do this. What are the possibilities of small but movable machines? They may or may not be useful, but they surely would be fun to make.

Consider any machine---for example, an automobile---and ask about the problems of making an infinitesimal machine like it. Suppose, in the particular design of the automobile, we need a certain precision of the parts; we need an accuracy, let's suppose, of 4/10,000 of an inch. If things are more inaccurate than that in the shape of the cylinder and so on, it isn't going to work very well. If I make the thing too small, I have to worry about the size of the atoms; I can't make a circle of ``balls'' so to speak, if the circle is too small. So, if I make the error, corresponding to 4/10,000 of an inch, correspond to an error of 10 atoms, it turns out that I can reduce the dimensions of an automobile 4,000 times, approximately---so that it is 1 mm. across. Obviously, if you redesign the car so that it would work with a much larger tolerance, which is not at all impossible, then you could make a much smaller device.

It is interesting to consider what the problems are in such small machines. Firstly, with parts stressed to the same degree, the forces go as the area you are reducing, so that things like weight and inertia are of relatively no importance. The strength of material, in other words, is very much greater in proportion. The stresses and expansion of the flywheel from centrifugal force, for example, would be the same proportion only if the rotational speed is increased in the same proportion as we decrease the size. On the other hand, the metals that we use have a grain structure, and this would be very annoying at small scale because the material is not homogeneous. Plastics and glass and things of this amorphous nature are very much more homogeneous, and so we would have to make our machines out of such materials.

There are problems associated with the electrical part of the system---with the copper wires and the magnetic parts. The magnetic properties on a very small scale are not the same as on a large scale; there is the ``domain'' problem involved. A big magnet made of millions of domains can only be made on a small scale with one domain. The electrical equipment won't simply be scaled down; it has to be redesigned. But I can see no reason why it can't be redesigned to work again.

Problems of lubrication

Lubrication involves some interesting points. The effective viscosity of oil would be higher and higher in proportion as we went down (and if we increase the speed as much as we can). If we don't increase the speed so much, and change from oil to kerosene or some other fluid, the problem is not so bad. But actually we may not have to lubricate at all! We have a lot of extra force. Let the bearings run dry; they won't run hot because the heat escapes away from such a small device very, very rapidly.

This rapid heat loss would prevent the gasoline from exploding, so an internal combustion engine is impossible. Other chemical reactions, liberating energy when cold, can be used. Probably an external supply of electrical power would be most convenient for such small machines.

What would be the utility of such machines? Who knows? Of course, a small automobile would only be useful for the mites to drive around in, and I suppose our Christian interests don't go that far. However, we did note the possibility of the manufacture of small elements for computers in completely automatic factories, containing lathes and other machine tools at the very small level. The small lathe would not have to be exactly like our big lathe. I leave to your imagination the improvement of the design to take full advantage of the properties of things on a small scale, and in such a way that the fully automatic aspect would be easiest to manage.

A friend of mine (Albert R. Hibbs) suggests a very interesting possibility for relatively small machines. He says that, although it is a very wild idea, it would be interesting in surgery if you could swallow the surgeon. You put the mechanical surgeon inside the blood vessel and it goes into the heart and ``looks'' around. (Of course the information has to be fed out.) It finds out which valve is the faulty one and takes a little knife and slices it out. Other small machines might be permanently incorporated in the body to assist some inadequately-functioning organ.

Now comes the interesting question: How do we make such a tiny mechanism? I leave that to you. However, let me suggest one weird possibility. You know, in the atomic energy plants they have materials and machines that they can't handle directly because they have become radioactive. To unscrew nuts and put on bolts and so on, they have a set of master and slave hands, so that by operating a set of levers here, you control the ``hands'' there, and can turn them this way and that so you can handle things quite nicely.

Most of these devices are actually made rather simply, in that there is a particular cable, like a marionette string, that goes directly from the controls to the ``hands.'' But, of course, things also have been made using servo motors, so that the connection between the one thing and the other is electrical rather than mechanical. When you turn the levers, they turn a servo motor, and it changes the electrical currents in the wires, which repositions a motor at the other end.

Now, I want to build much the same device---a master-slave system which operates electrically. But I want the slaves to be made especially carefully by modern large-scale machinists so that they are one-fourth the scale of the ``hands'' that you ordinarily manoeuvre. So you have a scheme by which you can do things at one- quarter scale anyway---the little servo motors with little hands play with little nuts and bolts; they drill little holes; they are four times smaller. Aha! So I manufacture a quarter-size lathe; I manufacture quarter-size tools; and I make, at the one-quarter scale, still another set of hands again relatively one-quarter size! This is one-sixteenth size, from my point of view. And after I finish doing this I wire directly from my large-scale system, through transformers perhaps, to the one-sixteenth-size servo motors. Thus I can now manipulate the one-sixteenth size hands.

Well, you get the principle from there on. It is rather a difficult program, but it is a possibility. You might say that one can go much farther in one step than from one to four. Of course, this has all to be designed very carefully and it is not necessary simply to make it like hands. If you thought of it very carefully, you could probably arrive at a much better system for doing such things.

If you work through a pantograph, even today, you can get much more than a factor of four in even one step. But you can't work directly through a pantograph which makes a smaller pantograph which then makes a smaller pantograph---because of the looseness of the holes and the irregularities of construction. The end of the pantograph wiggles with a relatively greater irregularity than the irregularity with which you move your hands. In going down this scale, I would find the end of the pantograph on the end of the pantograph on the end of the pantograph shaking so badly that it wasn't doing anything sensible at all.

At each stage, it is necessary to improve the precision of the apparatus. If, for instance, having made a small lathe with a pantograph, we find its lead screw irregular---more irregular than the large-scale one---we could lap the lead screw against breakable nuts that you can reverse in the usual way back and forth until this lead screw is, at its scale, as accurate as our original lead screws, at our scale.

We can make flats by rubbing unflat surfaces in triplicates together---in three pairs---and the flats then become flatter than the thing you started with. Thus, it is not impossible to improve precision on a small scale by the correct operations. So, when we build this stuff, it is necessary at each step to improve the accuracy of the equipment by working for awhile down there, making accurate lead screws, Johansen blocks, and all the other materials which we use in accurate machine work at the higher level. We have to stop at each level and manufacture all the stuff to go to the next level---a very long and very difficult program. Perhaps you can figure a better way than that to get down to small scale more rapidly.

Yet, after all this, you have just got one little baby lathe four thousand times smaller than usual. But we were thinking of making an enormous computer, which we were going to build by drilling holes on this lathe to make little washers for the computer. How many washers can you manufacture on this one lathe?

A hundred tiny hands

When I make my first set of slave ``hands'' at one-fourth scale, I am going to make ten sets. I make ten sets of ``hands,'' and I wire them to my original levers so they each do exactly the same thing at the same time in parallel. Now, when I am making my new devices one-quarter again as small, I let each one manufacture ten copies, so that I would have a hundred ``hands'' at the 1/16th size.

Where am I going to put the million lathes that I am going to have? Why, there is nothing to it; the volume is much less than that of even one full-scale lathe. For instance, if I made a billion little lathes, each 1/4000 of the scale of a regular lathe, there are plenty of materials and space available because in the billion little ones there is less than 2 percent of the materials in one big lathe.

It doesn't cost anything for materials, you see. So I want to build a billion tiny factories, models of each other, which are manufacturing simultaneously, drilling holes, stamping parts, and so on.

As we go down in size, there are a number of interesting problems that arise. All things do not simply scale down in proportion. There is the problem that materials stick together by the molecular (Van der Waals) attractions. It would be like this: After you have made a part and you unscrew the nut from a bolt, it isn't going to fall down because the gravity isn't appreciable; it would even be hard to get it off the bolt. It would be like those old movies of a man with his hands full of molasses, trying to get rid of a glass of water. There will be several problems of this nature that we will have to be ready to design for.

Rearranging the atoms

But I am not afraid to consider the final question as to whether, ultimately---in the great future---we can arrange the atoms the way we want; the very atoms, all the way down! What would happen if we could arrange the atoms one by one the way we want them (within reason, of course; you can't put them so that they are chemically unstable, for example).

Up to now, we have been content to dig in the ground to find minerals. We heat them and we do things on a large scale with them, and we hope to get a pure substance with just so much impurity, and so on. But we must always accept some atomic arrangement that nature gives us. We haven't got anything, say, with a “checkerboard'” arrangement, with the impurity atoms exactly arranged 1,000 angstroms apart, or in some other particular pattern.

What could we do with layered structures with just the right layers? What would the properties of materials be if we could really arrange the atoms the way we want them? They would be very interesting to investigate theoretically. I can't see exactly what would happen, but I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do.

Consider, for example, a piece of material in which we make little coils and condensers (or their solid state analogs) 1,000 or 10,000 angstroms in a circuit, one right next to the other, over a large area, with little antennas sticking out at the other end---a whole series of circuits. Is it possible, for example, to emit light from a whole set of antennas, like we emit radio waves from an organized set of antennas to beam the radio programs to Europe? The same thing would be to beam the light out in a definite direction with very high intensity. (Perhaps such a beam is not very useful technically or economically.)

I have thought about some of the problems of building electric circuits on a small scale, and the problem of resistance is serious. If you build a corresponding circuit on a small scale, its natural frequency goes up, since the wave length goes down as the scale; but the skin depth only decreases with the square root of the scale ratio, and so resistive problems are of increasing difficulty. Possibly we can beat resistance through the use of superconductivity if the frequency is not too high, or by other tricks.

Atoms in a small world

When we get to the very, very small world---say circuits of seven atoms---we have a lot of new things that would happen that represent completely new opportunities for design. Atoms on a small scale behave like nothingon a large scale, for they satisfy the laws of quantum mechanics. So, as we go down and fiddle around with the atoms down there, we are working with different laws, and we can expect to do different things. We can manufacture in different ways. We can use, not just circuits, but some system involving the quantized energy levels, or the interactions of quantized spins, etc.

Another thing we will notice is that, if we go down far enough, all of our devices can be mass produced so that they are absolutely perfect copies of one another. We cannot build two large machines so that the dimensions are exactly the same. But if your machine is only 100 atoms high, you only have to get it correct to one-half of one percent to make sure the other machine is exactly the same size---namely, 100 atoms high!

At the atomic level, we have new kinds of forces and new kinds of possibilities, new kinds of effects. The problems of manufacture and reproduction of materials will be quite different. I am, as I said, inspired by the biological phenomena in which chemical forces are used in repetitious fashion to produce all kinds of weird effects (one of which is the author).

The principles of physics, as far as I can see, do not speak against the possibility of manoeuvring things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are too big.

Ultimately, we can do chemical synthesis. A chemist comes to us and says, ``Look, I want a molecule that has the atoms arranged thus and so; make me that molecule.'' The chemist does a mysterious thing when he wants to make a molecule. He sees that it has got that ring, so he mixes this and that, and he shakes it, and he fiddles around. And, at the end of a difficult process, he usually does succeed in synthesizing what he wants. By the time I get my devices working, so that we can do it by physics, he will have figured out how to synthesize absolutely anything, so that this will really be useless.

But it is interesting that it would be, in principle, possible (I think) for a physicist to synthesize any chemical substance that the chemist writes down. Give the orders and the physicist synthesizes it. How? Put the atoms down where the chemist says, and so you make the substance. The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed---a development which I think cannot be avoided.

Now, you might say, “Who should do this and why should they do it?” Well, I pointed out a few of the economic applications, but I know that the reason that you would do it might be just for fun. But have some fun! Let's have a competition between laboratories. Let one laboratory make a tiny motor which it sends to another lab which sends it back with a thing that fits inside the shaft of the first motor.

High school competition*

Just for the fun of it, and in order to get kids interested in this field, I would propose that someone who has some contact with the high schools think of making some kind of high school competition. After all, we haven't even started in this field, and even the kids can write smaller than has ever been written before. They could have competition in high schools. The Los Angeles high school could send a pin to the Venice high school on which it says, ``How's this?'' They get the pin back, and in the dot of the ``i'' it says, ``Not so hot.''

Perhaps this doesn't excite you to do it, and only economics will do so. Then I want to do something; but I can't do it at the present moment, because I haven't prepared the ground. It is my intention to offer a prize of $1,000 to the first guy who can take the information on the page of a book and put it on an area 1/25,000 smaller in linear scale in such manner that it can be read by an electron microscope.

And I want to offer another prize---if I can figure out how to phrase it so that I don't get into a mess of arguments about definitions---of another $1,000 to the first guy who makes an operating electric motor---a rotating electric motor which can be controlled from the outside and, not counting the lead-in wires, is only 1/64 inch cube.

I do not expect that such prizes will have to wait very long for claimants.

Richard Feynman's "Tiny Machines" Talk:

Here is an updated version of Richard Feynman's classic talk from 1984.

*

Feynman's offer did not go unnoticed and interestingly, in less than 6 months after Feynman laid the bait, an electrical engineer called Mr. William H. McLellan had actually invented a motor 1/64 of an inch long!

Rather embarrassed, Feynman signed over a $1,000 check and stating that he did not expect somebody to accomplish this so soon and was disapointed that no knew manufacturing techniques had to be developed to create such a tiny machine part.

Feynman then stated, rather shrewdly, to people that he would now not make good on his other offer of $1,000 to the first person who would write the first page of a book 1/25,000 times smaller in scale.

The reason? Feynman had gotten married and bought a house during those 6 months!

Feynman had little to worry about, for it took until 1985 when a graduate student called Tom Newman claimed the prize when he wrote the first page of Charles Dickens' A Tale of Two Cities at the required scale, on the head of a pin with a beam of electrons:

The difficult part of this is of course reading nanoscale print on the head of a pin. How did he do it? Why with an electron microscope of course, just as Feynman himself predicted way back in 1959!

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Saturday, August 10, 2013