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This is about science produced by the California Institute of Technology and originally broadcast by station KPP C. Pasadena California. The programs are made available to the station by national educational radio. This program is about fall out with host Dr. Robert McGregor Lee and his guest Dr. Melton Placide professor of engineering science. Here now is Dr. McGregor since the first public announcement of the development of nuclear devices the public has come to heard here the expression fallout. I wonder if we might start our conversation by a few remarks about what we mean by far out in the what is it composed. Well the plot is composed of. Radioactive materials which are produced as a result of the nuclear explosion and the ones which are important are relatively few in number. These are I
presume things that have been heard many times in the past. Substances such as Strontium 90 and cesium 137 and IDM 131. These are all fission products. The one of particular concern to the study that I've made recently is carbon 14 which is produced either by a fission process or by a fusion process. Are these materials and chemical species produced as a result of a nuclear event produced from the device itself or is it the effect of the device on the environment such as the atmosphere. The first ones I mentioned that is the strontium 90. And the cesium 137 and the high Dean 131 are produced as a result of the fission process itself while
the carbon 14 the radioactive carbon is produced as a result of the emission of neutrons which accompany the explosion into the atmosphere. And what way are these nuclear isotopes harmful to us I presume that this is really the implication of the thought question that some of these species can affect living things and what with us this damage take place. Well all of these radioactive materials produce biological damage and there are two classes of biological damage which they produce in general they're divided into somatic damage damage to genetic damage which is damage to the genetic material which is material that
perpetuates the right contains the information. Yes contain the genetic material that information which is passed on from generation to generation. You mentioned that a number of these isotopes were produced directly from the fission process itself or fragments of the products of the reactions. But you indicated that carbon was somewhat different that it was produced by the effect of the nuclear reactions on the environment. This is directly of the atmosphere. Yes the radioactive carbon are Carbon 14 is the consequence of a neutron. It is produced in a nuclear explosion being absorbed by a nitrogen nucleus in the atmosphere and becoming carbon 14. The same process occurs all the time. By the by means of cosmic ray neutrons which are coming into the earth's atmosphere from
outside the Earth. Where do these nuclear reaction products go. Are they by and large contained within the atmosphere itself to make it into this soil. What happens to them. Well this depends upon the level at which the nuclear explosion takes place. If it takes place completely underground then we don't have an escape of the radioactive material if it occurs right on the surface. A large fraction of the radioactivity is captured and locally and in the earth. Part of it going up into the atmosphere and if it occurs in the air as we call it an air burst then all of that goes into the atmosphere. And where in the atmosphere it goes depends on the size of the explosion. If it's a large explosion hundreds of. Look kilotons or megatons that say millions
of tons of TNT equivalent all of the activity is carried up into the stratosphere. The smaller explosions deposit their activity in the troposphere the lower part of the atmosphere. Does this influence the way in which these materials chemical species and isotopes are spread around and into other elements of our environment reservoirs of our environment if you have the radioactive material which is carried up into the stratosphere becomes worldwide in its distribution. Then it can move about quite freely on a global scale. Yes and it defuses and eventually diffused back into the troposphere or lower atmosphere from which it comes down to the earth primarily by means of rain. So that means and it gets into the ground and into the oceans bylined.
Yes by large into the oceans Yes. But what gets into the ground of course is still terribly important for the creatures that live on the land. Further what gets into the ocean. It would be quite diluted because of the shipment volume of the ocean. Yes the how does one determine what some of these products are that result from a nuclear process. Is this something that one can predict or is it something that you can do my analysis. It's something that is known as a result of observations on the fission process in the laboratory but beyond that measurement of air samples are made and subjected to micro chemical analyses which are very precise actually small differences in the chemical composition of radioactive products from an exploding nuclear explosion. Give
information regarding the kind of nuclear bomb which has been exploded. So this is in fact a new monitoring tool too. Yes it certainly is. The whole technique is highly developed and quite accurate. So we know what these constituencies are in great detail. And you indicated that your more recent work was concerned with the question of the carbon 14. Is this a new problem that is recent in our thoughts or is it a problem that we've been concerned about for many years. Radioactive effects of carbon 14 have been of concern ever since the first nuclear explosions because the radioactive carbon goes with ordinary carbon. And it's part of every living organism and it's also part of genetic material so that it could have serious
genetic effect. Even though the level of level of activity in radio carbon is quite low mostly because carbon 14 radio carbon has such a long half life and it lasts for fifty seven hundred years and still you have half of what was originally present. Right. Then we've known about this problem and been concerned with and grappling with it for some time. Are there any recent sources of interest in the subject that we knew to intensify in our own investigations. Well the radio carbon acts as a tracer for the exchange of carbon which is going on all the time between what we call the various reservoirs of the earth. And what might these be M..
Well the other end of the identifies reservoir is the first reservoir is the one in which the radio car radio carbon is formed that is the atmosphere. And this if one wishes can be divided into the stratosphere or upper atmosphere and the troposphere and there's an exchange between these two parts of the atmosphere then the there is the land biosphere an important reservoir for for us that is. Reservoir which consists of all living things on the land and they are of course exchanging carbon for carbon dioxide and food materials with the atmosphere all the time. Then there is an exchange between the atmosphere and the sea which is divided itself into two reservoirs or the top layer of the sea where most of the
living organisms of the sea are located. Skin in the ocean about a hundred feet and fitness. And then there is the deep sea which is the rest of the oceans crim hundred feet from 100 feet on down which is an enormous volume of material. What is the internet is the exchange between the atmosphere and the deep space as seen then an indirect one through the top layer. This is what was believed up until quite recently. It seemed reasonable that the exchange between the atmosphere and the oceans would first take place between the atmosphere and the top layer of the ocean they call it the next layer and then the exchange to the deep sea would be between the mixed layer and the deep sea. What's caused us to change our view about this. Well recent measurements by Geo for the oceanographers. Who have been analyzing the
radioactive content of the carbon in the oceans these recent measurements have shown that near the poles there is a much more rapid exchange than one would allow or conceive if it took place through the mixed layer so that now this intermediate system so that the and there is some other evidence also aside from this more or less trace or evidence that the deep sea breaks through the mixed layer at the poles and has direct contact with the atmosphere. How large of an exchange element of the exchange is this direct interaction. Well the surface of the deep sea which is exposed in the polar region is only about a quarter of the total surface of the of the ocean. But the exchange
conditions are much more favorable Lare per unit area because they're only exposed over exposed ocean. Yes because the ocean is rougher there. So the surface is more ruffled and the winds are stronger as more area in a sense because there was more area exposed and more and better contact so that it goes a long way toward compensating for this reduced area. So the effect can be quite large then yes the effect can be quite large. This change in our ideas about the physical reservoirs for carbon and the exchange which takes place between them has some importance as you might expect for the rate at which radio carbon would be withdrawn from the atmosphere or the
land biosphere. Well in your recent work on this subject you mentioned already that we've detected some of these variations and in fact have had something of a surprise about the presence of carbon and the effect of the deep sea interaction with the atmosphere the direct interaction. Has your work been experimental in this nature is it can theoretical methods be applied here. This work that we've done is entirely. Theoretical or analytical. And one adopts a reasonable mathematical description and then follows it through to the conclusion that one can get in this way. We have predictions of the rate at which an excess of radiocarbon such as would be produced by a nuclear explosion would be withdrawn from the atmosphere and the land
biosphere. And just to know how does one approach such a problem in a theoretical basis. You mean you mention a mathematical representation. This would be of the reservoirs and exchange processes between them. Yes we have measurements on the B. Specific activity as it's called or the fraction of carbon which is radioactive carbon in these various reservoirs and these are measurements not these are measurements and they're rather delicate ones because the amount of radioactive carbon carbon 14 is very small. And then we adopt a very simple and reasonable picture of a reservoir much like a black box out of which carbon comes and into which carbon goes and takes a very simple and let you get the amount of carbon which can come out of a reservoir just
proportional to the amount that's in there. And then one gets rather rather simple relations which can be solved and give. Prediction as to how a pulse and power increase in the amount of radio carbon would be reduced so that these exchange so that you can use a model then to predict what would happen to a burst as you say of some nuclear device which is maybe released which in turn produces a carbon 14 and then the model allows you to predict how this Carbon 14 is distributed and how it affects the concentration of different reservoirs over a period of years. More than emphasizing their weight it's distributed. We are interested in the details of the rate at which it changes with time. Within a given reservoir we don't try to examine
the distribution over that reservoir but rather how it leaves or enters a given reservoir and the ultimate thing of interest for this study is the rate at which it leaves the atmosphere and the land biosphere and goes into the deep sea where it essentially stays until it all disappears. I seen what sort of results can one get from such a study now you've indicated that you can determine the rate at which it disappears into the ocean and how does then one relate this to the question of the influence of the biosphere and eventually how to fix living things. What are we looking there for there. What we're concerned about aside from the problem is a physical exercise that our description of a global property of the earth and its reservoirs is the increase in genetic damage which would result from
depositing excess radio carbon say as a result of a nuclear explosion. And. To determine how much damage genetic damage is produced by a given amount of radio carbon is a very difficult process. And what we do instead is to compare it to the natural background of radio carbon sensors radio carbon being produced by cosmic rays we have a natural background that we know the one that we have survived and accommodated since the beginning of time. And one can compare what kind of explosion would give you something which would equal this. So you use the natural background as a sort of a yardstick that it's right as a quantity that we can relate these new and additional effects to a kind of quantitative result
as your study indicated today. So all these studies indicate that it actually takes a while what would seem like a fantastic amount of. Of nuclear explosive to match the natural background over the long period this is what is of significance for the race so the speak is what the long term genetic damage is following an increase as a result of nuclear explosion so that in a sense there is a slight courage meant that the as far as radio carbon goes and the genetic damage it requires a rather large amount of nuclear explosive to produce a significant effect. Could you indicate some magnitudes here.
Quelling using megatons as our unit of nuclear explosion. If we were to look at the three hundred years after the explosion if a total of sixteen hundred megatons were deposited this would give. An amount of radioactive damage from carbon 14 which would match the natural background so that it would have been just doubled and yes it would have been years doubled to get a yardstick again on the quantity of the sixteen hundred megatons how many tons of an effect have been exploded so far in the atmosphere by all the parties involved. Most of the nuclear explosions have been already carried out have been carried out by the United States and the USSR and up until the time that the test ban
went into effect this amounted to a five hundred megatons. Now as you know there are some there are some new developments which bring new attention to the problem. Following the explosions by the French and the Chinese. Yes and these are as yet relatively small compared with that amount and together the French and Chinese have exploded appreciably less than a megaton. These are relatively small values total amounts that are relatively small compared to the figures that you quoted and yams of what it would take to double the back right. So that from the. Then is it in the long term here for the carbon 14. Of course with such amounts that needed in the atmosphere and therefore available to the immediate reservoir of the atmosphere you would expect other isotopes which would be harmful to have already
had some introduction to our food supplies and so on. That is you're speaking now of the somatic damage which will be produced yet. These would be very intense over a relatively short period and would of course be quite harmful. That is the strontium 90 is similar to calcium deposits in the bone produces an increased chance of bone damage. Various kinds of cesium 137 which is also an abundant fission material is not perhaps so serious because it does not reside in the body for a very long period as does something like strontium deposit in the bone. I have seen rather serious material since it goes selectively to the thyroid but it has a very short life and.
Would it have like being only about eight days. You know it's so silly. I might say these fission products of the kind which I mentioned aside from carbon 14 became relatively rapidly in seven hours a week eight and half and so every seven hours you get a power of a half that goes a half a quarter and so on Bryant so the several thousand years half life of the carbon 14 then becomes of much of a long term interest to us and also because of the fact that it has on the organic molecules and materials of our bodies and food. Yes. And primarily it would be something of concern from the genetic point of view is that if the carbon radioactive carbon is picked up by an organic molecule such as DNA for example one what we've been hearing about there is important to genetic character. What is the nature of the damage or how might the damage proceed.
Well it would certainly proceed in the usual way. The carbon the radioactive carbon nucleus an electron or a Beta Ray which deposits energy in the material and thereby produces damage disrupting bombs atomic bombs right. There is also a possible second mechanism which has been discussed suggested since the carbon 14 when it emits an electron changes its chemical composition and becomes a nitrogen. All of the sudden the DNA chain finds and I don't know where it shouldn't be in a very peculiar spot where the problem that it was so that this presumably would be damaging in the sense that it destroys or affects the information content of them. Yes so this would make the carbon 14 in the DNA molecule more damaging than
an ordinary radioactive damage process would be this would be then the damage to a particular molecule but then I should think for a larger living system. That it would take a number of many such damages or damage molecules or altered molecules and I presume it would also be determined by where the molecule was and what function it performed. Yes and of course I think we must keep in mind that we talk about genetic damage and that many of these are very small and might not be detected. On the other hand if this is the kind that will propagate relatively easily and the more serious ones tend not to. Well thank you very much for your very interesting remarks and certainly the encouraging results of your investigation.
About science
About fallout
Producing Organization
California Institute of Technology
KPCC-FM (Radio station : Pasadena, Calif.)
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University of Maryland (College Park, Maryland)
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This program focuses on the definition of fallout. The guest for this program is Milton Plesset.
Interview series on variety of science-related subjects, produced by the California Institute of Technology. Features three Cal Tech faculty members: Dr. Peter Lissaman, Dr. Albert R. Hibbs, and Dr. Robert Meghreblian.
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Guest: Plesset, Milton S. (Milton Spinoza)
Host: Hibbs, Albert R.
Producing Organization: California Institute of Technology
Producing Organization: KPCC-FM (Radio station : Pasadena, Calif.)
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University of Maryland
Identifier: 66-40-36 (National Association of Educational Broadcasters)
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Duration: 00:27:32
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Chicago: “About science; About fallout,” 1967-05-12, University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC, accessed January 23, 2021,
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APA: About science; About fallout. Boston, MA: University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Retrieved from