A: I came to Berkeley as a graduate student in 1934, just at the time that Fermi and coworkers in Rome were bombarding uranium with neutrons in the attempt to produce elements with atomic numbers greater than that of uranium, number 92. They thought they'd done this, but as you know, they were wrong. And Hahn and [Strassman] showed that these were due to fission products in December, 1938. I was interested in this during all those years. And when the opportunity presented itself, in 1940, to enter the field, I and my coworkers bombarded uranium with deuterons in order to try to produce the first element, beyond neptunium, that had been produced by and identified by McMillan and Abelson in 1940.

And we bombarded uranium with deuterons. I was an instructor, and I had as a coworker an instructor named Joseph Kennedy and a graduate student named Arthur [Wall]. And we carried on the work that had begun by Edwin McMillan, and we bombarded uranium with deuterons on December 14, 1940. And we found an alpha particle-emitting product, which we were able to identify as the element with the atomic number 94. And we made that critical chemical identification on the night of February 23-24, 1941. And that constituted the discovery of element 94, which a year later we gave the name plutonium.

Q: Now, plutonium doesn't occur naturally in the world, as far as people know?

A: No. Plutonium doesn't exist naturally. Oh, a very, very small amount, due to the action of neutrons on uranium. You know, one part in a million million of uranium ores. But not a practical source.

Q: One of your things that you were assigned to do was to characterize this new element. To find out something about it? Your job when you'd found plutonium was to actually work out its chemical properties?

A: Yes. Our program was one research to increase knowledge. We were not supported by the federal government. It was just our own university. But then we went on with the addition of another young physicist and bombarded uranium with neutrons in large quantities, using the 60 [N] cyclotron, and were able to identify the isotope of importance, isotope with the mass number 239. The one we'd first found was the plutonium with the mass number 238. We found that the plutonium-239 was fissionable, with slow neutrons, in an experiment that we conducted on March 28, 1941. And that, of course, opened up the whole field of the possibility of this new element being a source of nuclear energy.

And we reported this result to Washington. And they were very excited about it, and then they began to support our work. And we carried it on and made more careful measurements. And we showed that the probability for fission with slow neutrons of our plutonium-239 was even greater than that of the famous uranium-235, the fissionable isotope of uranium.

And this led to the plutonium part of the Manhattan Project. Pearl Harbor came along and we entered the war, and I was asked to move to Chicago to work on the development of the chemical processes for the production of plutonium in quantity, as it would be produced in a chain-reacting pile, as they called it, a chain reactor. The feasibility of the chain reaction using natural uranium was demonstrated by Enrico Fermi and coworkers on December 2, 1942. And then I had the responsibility of working out the chemical processes that would be used for the separation of that plutonium from the huge quantities of fission products in uranium. The process that went into operation in the pilot plant at Oak Ridge, Tennessee, and then in the production plant at Hanford, Washington. I arrived in Chicago at the so-called Metallurgical Laboratory on my 30th birthday, April 19, 1942. And then I gathered these young people around me to carry on this research, to find a separation process. And I was the oldest member of my group.

Q: So the big question at that time was whether it would be easier to enrich the uranium-235 or to separate the plutonium-239. Is that the issue?

A: There were the two approaches, then, to fissionable material that might be used in a nuclear weapon. One was to separate the uranium-235 from the abundant 238--uranium-235 present only to the extent of seven tenths of a percent--by the difficult methods of isotope separation. And then the other approach that was opened up by the research, of my research with my coworkers, was the plutonium approach, which had the advantage that if you could produce it in a chain reaction, you had a different element so that you could chemically separate it. You see, the separation of isotopes couldn't be done by a chemical procedure. It was a very complicated procedure, or several different procedures were investigated. Very, very difficult. And the thought was that through the plutonium approach, we'd use the methods of ordinary chemistry and be able to make the separation.

So both approaches were used. And, well, both were successful. The electromagnetic method of separating uranium, together with a little bit from what they call the gaseous diffusion method, led to enough uranium-235 for use in the bomb that was used on Hiroshima. And then our method, the plutonium approach, produced enough plutonium to test it as an explosive ingredient at Alamogordo on July 16, 1942. And then enough more was produced so that it could be used as the explosive ingredient of an atomic bomb on August 9, 1945.

Q: As a young chemist, in your work at that time, did you think that plutonium was an immensely significant discovery?

A: Yeah. Well, I've often been asked the question. And all I can say, I didn't ruminate about it. We'd made a discovery. Our aim was to increase knowledge about the periodic table. We were excited that we'd produced a new element. And we were, of course, quite excited to be able to show that it had an isotope that was fissionable and, hence, could be a source of nuclear energy. But we didn't stop to ruminate about it [and] say, "Look, we're going to change the course of the history of the world." We just didn't do that.

Q: But after the war, when people started to talk about the peaceful use of atomic energy, did you, like other physicists, think that atomic energy would be a very important discovery for mankind?

A: Well, of course, as the war was drawing to an end, and actually the war in Europe had been brought to an end when the question of the use of the atomic bomb against Japan came up. I was a member of the group under the chairmanship of James Franck, who wrote a report advocating that the bomb be demonstrated before it was used--this was the famous Franck report--and, hence, giving the possibility that it wouldn't be necessary to use it. We don't know, however, whether this report actually got to President Truman, and in any case, he did give the order to go ahead and use the bomb.

Now, with respect to my thoughts about the development of atomic energy after the war, I was of the same opinion of many others that this would be a very useful source of energy to develop, to produce electricity and so forth. But I wasn't among those who thought that it would come right along very soon. I could see it was a very complicated process, and that it would take a number of years before it could be developed to that point. And that is the case, of course. It was 20 years or so before reactors were built capable of producing electricity from the nuclear source.

Q: Now, in terms of the vision of atomic energy for peaceful purposes, was the notion of using plutonium, of reprocessing and using plutonium, part of the original vision?

A: Yes.

Q: Therefore, if you're going forward with an atomic energy program just based on uranium-235, it's obviously finite. If you can make use of the plutonium that's created in reactors, it's bigger.

A: Yes. Well, of course, the reactors that were built to produce electricity then used uranium-235, enriched from the seven tenths of a percent (its natural abundance in uranium) to about three percent. And then it was possible to build reactors using water as the coolant and the heat transfer medium, that would go to the turbines to produce electricity. There was almost immediately, the possibility that it would be possible to use plutonium as an intermediate in what came to be known as a breeder reactor, that is, the uranium-235 chain reaction operating to produce neutrons that some of which could be absorbed in the uranium, abundant U-238, to form plutonium. And then that plutonium could be used as a fuel to continue the reaction. And if one could produce, as you were burning plutonium, more plutonium than you consumed, then you could continually replenish the core and have a reactor that was, in effect, using as a fuel the non-fissionable uranium-238, through the plutonium as an intermediate. We thought that that approach would be possible. We thought it would be a long-range matter. And as it turns out, it's longer range than even we thought. It's a very complicated approach.

Q: But if you can make use of that unfissionable U-238, the amount of fuel in the world is much bigger.

A: Yes. If we could develop the breeder reactor so that we could use the non-fissionable uranium-238 via the fissionable plutonium-239, then we would have hundreds of times more fuel. And not only that. [B]ecause of its abundance, it would be possible to use lower grade uranium in ores. It would be economically feasible to do that. So you'd have much larger supplies of uranium, enough to last, I don't know how long, thousands of years, probably, if the breeder reactor was developed.

Q: Now, in the '70s, during the Carter era, the decision was made that this country wouldn't reprocess nuclear fuel, spent fuel rods. How significant is that?

A: Yes. In the late '70s, the Carter administration, a fellow nuclear scientist, made the decision that the United States should stop the development of the breeder reactor, with the hope that this would serve as a model to the rest of the world that they wouldn't develop the breeder reactor. The idea being that in the development of the breeder reactor, you would produce a lot of plutonium, which might be thought would be used in nuclear weapons, and therefore could lead to the proliferation of nuclear weapons. President Carter thought that if he stopped the development of the breeder reactor in the United States, that would serve as an example and lead to the cessation of the development of breeder reactors throughout the world. And then that would have this adverse effect on nuclear proliferation.

But it didn't work out that way. The other countries didn't follow the lead, and they have gone ahead with the attempts to develop the breeder reactor, and of course, with nuclear power.

Q: Now, was he right in worrying about the proliferation aspect? Or was the fear that plutonium from commercial reactors could be turned into bombs, was that an exaggerated fear? How easy is it to do this?

A: Well, the plutonium is not in a good form for using in bombs, because it has too high a concentration of the other isotope, plutonium-240. But the real question is that this is a problem that has to be solved anyway. You don't solve it by trying to stop the development of any particular form of nuclear energy. Nuclear energy is a source of electricity that's very attractive to many countries in the world. And the natural result is that they went ahead and are going ahead in the development of this source of energy.

Q: So it was futile?

A: President Carter's idea of stopping proliferation through the stopping of the breeder reactor, no, it didn't work.

Q: Now, plutonium, this substance that you did your work on, has come to be demonized in our society, both for its proliferation potential, but also many environmentalists talk about it as "the most toxic substance in the world."

A: The number of (I guess you'd call them) environmentalists characterize plutonium as the most toxic substance in the world. That, of course, is nonsense. There are many toxins and viruses that are more toxic than plutonium, that lead to immediate death if taken in amounts equal to what they're talking about as the toxic amounts of plutonium. There have been scientists, as a result of accidents, dating clear back to the war, who have ingested plutonium up to the level of what is considered tolerable amounts. And some of those are still alive, 50 years later. Whereas, if they had ingested an equal amount of some viruses or toxins, they would have died immediately. So it's just nonsense to speak of plutonium as the most toxic substance in the world. It's not anywhere near it, not in the ballpark of being near that toxic a substance, when people who ingested it 50 years ago are still alive.

Q: Tell us something about plutonium. Most people have never seen it. What is it? A metal? Talk about its properties. If you were holding a piece now, what would it look like?

A: Well, plutonium is in a form of a metal. Of course, due to the radioactive decay, it's warm. I've only one time in my life held a chunk of plutonium in my hands. And I remember handling a chunk of it. And it is warm. But it just looks like any other metal. Not much different than a chunk of metallic iron, for example.

Q: What color is it?

A: Dark metallic color. Color, as I say, not much difference than a metallic iron. Pure iron, I mean. Not steel.

Q: Now, people talk about its radioactive properties. How does it compare with other radio-isotopes? (When we were at Idaho Falls, they had a little piece of plutonium, and we did the experiment with the piece of paper, where we showed you could shield that.)

A: Yes. Well, plutonium emits alpha particles, which only have a range, you know, about that far in air. And so it isn't like some radioactive substances, like say cobalt-60 or an isotope like that, that emits gamma rays that are much more penetrating. Plutonium emits a low level of gamma rays, but its radioactivity is mainly due to the emission of what we call alpha particles. That is, helium nuclei that don't travel very far, but that do cause all of their ionization in that very short distance. And therefore, as the alphas plow their way through the metal, the kinetic energy is changed into thermal energy. And that's what leads to the heating of a sample of plutonium metal.

Q: So the danger to somebody would not be holding plutonium in their hand. It would be ingesting it, would it?

A: No. If one holds a piece of plutonium in one's hands, it (as I say, it's coated so that the alpha particles ... can't come out and enter your hands) is not very dangerous. I mean, it emits a little bit of gamma radiation. I mean, if you held it there all day or something like that, you'd get some radiation.

Q: So the danger is in ingesting it, is it?

A: The danger is in the ingestion. And these alpha particles then goes to various parts of the body--the bones and the organs like the liver and so forth. And therefore, there is a certain level that's called a tolerance level, that you shouldn't exceed. But as I say, it, even in those cases, it's an adverse health effect that takes place over years of time, not like many poisons that act much faster.

Q: Now, talk about the half-life of plutonium. What is a half-life?

A: The half-life of plutonium is 24,000 years. That means every 24,000 years, half of the plutonium has decayed to its daughter. And by the way, in our very first experiment back in March of 1941, we estimated the half-life as 30,000 years. And that's what we reported in our report. So that's not a bad determination. And I like to say that we had the advantage that we had so many errors that they canceled each other. So we came out with a good value.

Also in the report that we finally sent to Washington in March of 1942, on the chemical properties, under the authorship of my graduate student, Arthur Wall and I, we proposed the name for plutonium. See, the uranium had been named after the planet Uranus, and neptunium after the plant Neptune. So we thought we would name plutonium after the planet Pluto. Now, we probably should have used the base "plut" and called it plutium. But we liked "plutonium" better, so we named it plutonium. And then the chemical symbol should have been Pl. See, plutonium, Pl. But we liked Pu better, so we gave it ... the symbol Pu. And we thought that we would be criticized for that after the war, when it could be published. But nobody said a word.

We almost made a mistake, a terrible mistake, because we thought we'd reached the very top of the periodic table, that nobody would ever go higher than atomic number 94. So we thought we should name it "extremium" or "ultimium", you know, the ultimate. Think how foolish we would have been if we had given such a name, now. Because after all, they've gone on and on, well, clear up to element 112 now. There are 20 elements beyond uranium now, 20 transuranium elements. And plutonium is only the second one. So we certainly would have been very foolish if we had done that.

Q: But is it true still to this day, it's only uranium-235 and plutonium-239 that are fissile? Are they unique?

A: There is another isotope like plutonium-239, produced in the bombardment of thorium with neutrons. And thorium-232 absorbs a neutron, becomes 233, and then there are couple of electrons emitted and goes to uranium-233. And that's also fissionable with slow neutrons. and disposition of plutonium, actually the honorary chairman and a participating member of the panel, appointed by the American Nuclear Society. And we came out with a report on the management and disposition of plutonium. And we recommended that it be burned as fuel in what they call "mox form". We are recommending that the plutonium be burned, that is, it be mixed with uranium in the oxide form. This is what's called mox, "m" standing for the metal and "ox" for oxygen. And the energy, of course, converted into electricity by burning it this way, rendering it unsuitable for nuclear weapons.

Q: You mean, using it in a commercial reactor?

A: In civilian reactors. And then of course there's a problem there. It has to be acceptable to the operators of civilian reactors and to some extent, the general public. But there are a number of operators of nuclear reactors who have volunteered to do this. And this renders the plutonium relatively unsuitable for use in nuclear weapons.

Another approach is to take the plutonium from the cores of nuclear weapons and bury it. And the suggestion has been made that it be buried along with radioactive fission products, so it would be hard to get at. But the problem with that approach is that no matter where you bury it, it's still there. And some time in the future, somebody can go down and get it and retrieve it. And we have to come up with a method of disposal that will be acceptable to the Russians as well. And they do not trust us to bury it, because they would think that it would be retrievable for us, for use in nuclear weapons. And they favor this mox approach, where you burn the stuff and make it relatively unsuitable for nuclear weapons.

There should be a decision on this made later this month, December of 1996, as to which method of disposal will be used. The groups I'm on are recommending very strongly that we use the mox approach to burn the plutonium. And maybe take only some of the plutonium scraps and so forth, and dispose of them in radioactive depositions with strongly radioactive fission products.

Q: Now, this recommendation is only for weapons-grade plutonium. It isn't for reactor plutonium.

A: Our recommendation is chiefly for weapons-grade plutonium. But it is also possible to do the same with plutonium that comes from reactors. Actually, there's more plutonium that is produced in reactors than there is weapons-grade plutonium. I think there's about a quarter of a ton per year of plutonium produced in a 1,000-megawatt reactor. So you can see how much plutonium is produced there. But that could also be reused in a mox form and rendered even more unsuitable for use in nuclear weapons.

Q: And in the rest of the world, they use that already, don't they? In France, for example, they already use the mox process.

A: Well, in France, of course, they do have this approach. And they are intending to use, burned plutonium in this manner. And this is, as I say, the way that Russia prefers to render unusable its stock of plutonium. This is a decision that needs to be made. We just have to make this plutonium unusable, essentially, for nuclear weapons.

Q: Does this country need nuclear energy? And does the world need nuclear energy?

A: Oh, I think the world definitely needs nuclear energy. As I said, about 17% of all the electricity in the whole world is produced from nuclear energy. And as time goes on, we're going to run out of fossil fuels. And other sources are really not going to be economic so that they can fill the gap. Actually, what I think is that we're going to have to develop all sources of energy: nuclear energy, clean up the fossil fuel approach, and develop so-called renewable sources of energy. In the future, the world's going to need all of these, particularly the developing countries.