Mr. HOLIFIELD. Before you leave the fission products, could you describe the beta rays and the hazards, and the half life, then the gamma rays and their span of hazard and their half-life duration? You may want to bring in the strontium 90 in the thermonuclear field rather than in the fission field, but treat all of those and give the record some sort of an evaluation of the degree that we have to consider in building these shelters.

Dr. TOMPKINS. I will give myself 3 minutes and take a try and see if I can come close to succeeding.

We are interested in radioactive materials because of the nuclear radiation which is given off by them. There are more than 3 types actually given off but there are three major types of direct concern. First, the beta radiation which, for all practical purposes, has significance in two counts: It can cause a burn on the skin if the radio element is deposited on the skin. If the radioactive elements are taken inside of the body, they can cause somewhat higher intensity direct exposure to the sites very close to where they are deposited.

This is the origin of the problem with strontium 90 which deposits in the bone marrow and produces short-range beta radiation.

The second major cause of concern is the gamma exposure type, or gamma radiation type. For all practical purposes, gamma rays are, for purposes of this discussion at lease, the same as that which you would get from an X-ray machine. They travel large distances in air, they are capable of penetrating through and into dense matter. They are deleterious to the human body. It is the gamma radiation which is of primary concern to all emergency operations of civil defense. This threat of gamma radiation is the one which must be defeated because all other threats are secondary to it.

Mr. HOLIFIELD. Give us the half life of the beta and gamma, if

you can.

Dr. TOMPKINS. I was hoping to duck that question, Mr. Chairman. Mr. HOLIFIELD. I know you scientists want to be absolutely accurate but give us an approximation. A relative approximation, I mean. The beta is short-lived, we know that.

Dr. TOMPKINS. The half life by definition is the time it takes for any particular radio isotope to decrease in intensity to one-half of its so-called initial value. Every isotope has its own characteristic half life. This is independent of the nature of the radiation that it emits. With the fission product mixture the so-called half life is usually characterized by the T-1.2 rule.

I think the testimony at your Joint Committee summed this up by saying that every time you double the time you decrease the radiation intensity by approximately a factor of 7-do I have this right now?

Mr. SHEPHARD. Seven to a half.

Dr. THOMPKINS. Another way to put it, the half life of radioactive decay is roughly equal to the age. After 5 minutes the radiation intensity will decrease in the next 5 minutes to one-half of that value. This, then, gives you a starting time of 10 minutes after detonation. In the next 10 minutes, it will go down by another half.

The age is now 20 minutes and the next 20 minutes it will by another half, and so it goes.

go down

The significant point is that the rate of decay at early times after detonation is exceedingly fast. It is during this period that the intense radiation intensities are encountered.

So the greatest threat from fallout is always during the relatively early periods. This is why the massive doses are obtained in a matter of a few hours, to a few days.

Mr. HOLIFIELD. And this is why the shelter can render such a great service. The radiation shelter can render a great service even if it only amounts to a few hours or a couple or 3 days.

Dr. TOMPKINS. Yes, sir.

Mr. HOLIFIELD. It can give this fast decay a chance to perform its function of reducing the intensity of radiation before the human body comes outside to be exposed to it.

Dr. TOMPKINS. Yes, that is correct. But that is also why shielding is an absolute essential. There is no alternative to this as a basis of protection.

Mr. FASCELL. At the present time.

Dr. TOMPKINS. I will stick my neck out, sir, and say for some time

to come.

The reason for a shelter is for the same reason you put a shield around a reactor. In case you do not know it, you do not get intensities from reactors that are very much in excess from what you would get at peak intensities from fallout.

Mr. HOLIFIELD. Your beta contamination goes down very fast.
Dr. TOMPKINS. Yes, sir.

Mr. HOLIFIELD. It is over in just a few hours?

Dr. TOMPKINS. And so is the gamma.

Mr. HOLIFIELD. Your gamma is over in a short length of time. What is the general half life on that?

Dr. TOMPKINS. I would like to be sure to try to keep this straight, Mr. Holifield.

Both the beta and the gamma radiations decay approximately equally. Technically, in terms of pure science, this is not quite right but the rate of decay affects both types of radiation.

Mr. HOLIFIELD. But the penetrating quality is different, is it not? Dr. TOMPKINS. This is the point. At all times, the fallout mixture is emitting both beta radiation and gamma which means that if you are in the open and get the full brunt of the gamma radiation, you are getting penetration to the whole body. Also, if you get light shielding you are getting penetration through the whole body through the shield.

If you are exposed momentarily and get some of the fallout material on your hand, and then get under a shield and carry it with you, the beta radiation coming from the particles themselves are quite capable of causing a burn.

This was the cause of the burns which you saw on the natives because they were taken from the field prior to the time that the gamma radiation had had its major effect. They carried the fallout particles with them and there the short-range intensities or the beta particles superseded that of the gammas but you know that applied only to local skin burns and these things are present all the time.

It depends entirely on how you happen to brush up against them, what the relative significance becomes. That is why in radiological

protection so much is made of protective clothing. All this does is keep the particles off your body and thereby defeats the short-range beta hazard and reduces it to very managable proportions.

The gamma problem is not so easy to cope with. I would like to continue just a moment, if I may, in summarization.

The important characteristics of the fallout material are every bit as dependent upon the detonation medium as upon the nature of the weapon. Detonations in water create fallout material which are inherently soluble. Detonations on the ground, no matter what kind of ground, creates fallout materials much of which is relatively insoluble. This means it is not chemically available. These facts are minor in significance to the gamma radiation threat during early periods. They are tremendously significant to the process of subsequent removal, because water will stick to surfaces where big particles of dirt will not, but even more significantly, it is tremendously important in the later agricultural problem which is determined by the incorporation of these radioactive elements in the biological cycle and are taken up into food and ultimately wind up in the body.

Mr. HOLIFIELD. You are speaking now of the long-life deposits, strontium 90 and

Dr. TOMPKINS. Yes, and I am also speaking of the problems encountered in obtaining drinking water at relatively short times say the first month. Remember, the fission product mixtures contain barium and lanthanum isotopes which are as dangerous as strontium except for their half lives. They are present from the beginning to the end.

And the rate at which this material can become available to such things as drinking water sometimes becomes very, very significant in the ease with which you can handle them.

In summary, it is simply this: The fallout from water detonation is far more available biologically than fallout from land area. By a factor of about 2 to 5 in many cases. Fallout close in which creates the mammoth fallout threat which we have all heard discussed, is mostly large particles and is inherently insoluble.

Specifically, I am of the opinion that any land detonated fallout material which is inherently lethal will be associated with enough material to be visible and if any American citizen is worried that he will be killed by radiation from fallout and not know it is coming, I think they need not be worried simply because, from our mass activity relationships, we do not get that intense a fallout deposit in the absence of visible quantities of material.

Mr. HOLIFIELD. In other words, if the Japanese fishermen had realized what was falling on their ship and had washed it off and taken baths and washed their hair, there would have been a great deal of difference in the deleterious effects?

Dr. TOMPKINS. That is exactly correct and you need nothing but your eyes to tell you this. It was the fact that they did not recognize it was radioactive that got them into trouble.

I point these things out because it is this kind of information that we are pulling together specifically for the civil defense.

Mr. HOLFIELD. It would not apply to damage by neutrons?

Dr. TOMPKINS. No, sir.

In summary, I would say that fission materials are more dangerous than the induced radioactivities from neutrons created by fusion.

However, radioactivity is always present and quite often in quite significant quantities. The magnitude of the radioactivity problem can be changed markedly by the weapon design but it cannot be eliminated.

There is one characteristic of the fallout threat which I think should be incorporated in such a summary: The dangers are, exposure of the whole body to radiation from penetrating gamma, burn on the surface of the skin from material deposited on the skin coming from the beta radiation and, finally, the more delayed hazards of ingestion and so forth.

I do not want to go too deeply into this because Dr. Taylor will cover it far better than I, but in summary those are the three general classes of hazard.

The killer is the gamma, associated with close-in fallout. That is the major threat.

Mr. HOLIFIELD. Now, when you say close-in fallout, you put the meaning on that of the larger particles of debris which fall downwind from an explosion, usually, to distinguish that from the type of radiation that would go through the troposphere into the stratosphere.

Dr. TOMPKINS. Yes, sir.

Mr. HOLIFIELD. And it is this type of radiation primarily that we are concerned with in our protective shelters.

Dr. TOMPKINS. That is correct.

Mr. HOLIFIELD. I might go so far as to say that for all practical purposes it is the only one with which you are concerned, for protective shelters.

Dr. TOMPKINS. We can't do much about the other.

Mr. HOLIFIELD. They are relatively insignificant. If you properly defeat the gamma radiation from fallout, the others automatically take care of themselves.

The reverse is not true.

Mrs. GRIFFITHS. What does close-in mean in relation to a 20-megaton bomb?

Dr. TOMPKINS. This is strictly a line of demarcation between, I might say, worldwide fallout and so-called close-in. In the case of a 20-megaton weapon, it would extend to a distance of 350 miles. Mrs. GRIFFITHS. That is not very close.

Mr. HOLIFIELD. It is an important question you ask because if a 10-megaton weapon would contaminate 9,000 square miles, roughly speaking, downwind, a 20-megaton weapon would cover a greater area and this is why, when you disperse 150 weapons over the United States, you have a universal contamination, practically. There might be some areas that would escape some contamination and there would be many areas that would have light contamination, but there would also be a great many areas that would have much more than lethal and even overlapping. Instead of the lethal damage of four or five hundred roentgens, it might run as high as five or six thousand. Dr. TOMPKINS. That is correct.

Mr. HOLIFIELD. There are two features about the fallout patterns with which we are acquainted which have not been properly emphasized. The first feature is that the peak intensity never occurs at the crater. It occurs about 50 or 75 miles downwind from the crater.

It gets picked up, caught low on the wind and gets carried downwind. So the major intensity of the fallout threat that you are going to cope with is outside of the area of physical damage, and this is significant to all considerations of shelter, particularly where one considers relaxing the shelter requirement because of presumed distance from a potential target area.

And this is also, sir, why you start saving life close to the lip of the crater. By that I mean undoubtedly if it is a ground burst everything will be lost within the area of the crater, but very shortly outside of that crater, if you are underground, you do have an opportunity of saving life both from shock and heat as well as from radiation. One of the factors in that is that your peak intensity of radiation does not necessarily come near the lip of the crater but it may be carried to the first deposits of the heavier particles downwind. In layman's language that is roughly correct?

Dr. TOMPKINS. Yes, it certainly is. This is one point I did want to make, Mr. Holifield, because it is one which is certainly built into all the technical information we have but it has simply not been hauled out and stated quite as explicitly as I have stated it here. In other words, I am willing to stick my neck out and say the major residual radiation threat does not occur within the range of physical damage.

Mr. HOLIFIELD. From radioactivity.

Dr. TOMPKINS. Yes, sir.

Mr. HOLIFIELD. The life would be lost within the area of physical damage from heat and blast?

Dr. TOMPKINS. Well, this is significant, though, when it comes to shelter design criteria, this is the point I am making.

The second point I might make is that the long-range agricultural biological threat is quite different in its behavior from the penetrating gamma radiation threat.

Specifically after the deposit is all over, the contours defined by the external gamma radiation, with the customary roentgens per hour shrinks continuously with time.

Mr. HOLIFIELD. I think this is important enough to take an actual figure, if you can. Let us assume a very high intensity figure of 5,000 roentgens per hour for the first hour. Could you, without too much mathematical computation, tell me what the decline in that would be within a period of 10 hours?

Dr. TOMPKINS. From 5,000 per hour?

Mr. HOLIFIELD. Yes.

Dr. TOMPKINS. 10 hours, I think, is roughly a factor of 15.8, I believe. I would prefer to look it up for you, Mr. Holifield, you can pick it right off of the decay curves but I think it is better than a factor of 10 reduction.

Mr. HOLIFIELD. Wait a minute. Give us that in layman's language. It goes down from 5,000 to what?

Dr. TOMPKINS. In 10 hours I think it will go down to something on the order of 315.