Major Stebbins.

Mr. ROBACK. Major Stebbins, can you tell us when the revised "Effects" handbook will be published and available?

Major STEBBINS. It is in its final draft form now. For the past 6 or 8 months we have been actively engaged in preparing it under the editorship of Dr. Samuel Glasstone. It has been fully coordinated with technical people not only in the AEC, but in many of the Government laboratories and other contractors that have knowledge in this area.

The final draft has been submitted for the ultimate coordination between the administrative people in the Department of Defense and the AEC. I anticipate that it will be presented to the Commissioners of the AEC shortly.

Mr. ROBACK. The AEC has the editorial responsibility, do they? Major STEBBINS. Dr. Samuel Glasstone is the editor of the docu

ment.

Mr. ROBACK. Does he work for the AEC under contract?

Major STEBBINS. He is contractor to the AEC, and has been working very closely with us in the Defense Atomic Support Agency in the actual physical preparation of the material.

Mr. ROBACK. Now, do you regard the material in this handbook as the essence of authoritative information in regard to nuclear weapons effects?

Major STEBBINS. I think

Mr. ROBACK. Let me ask you, why do you put out this handbook? Major STEBBINS. It is a document which the Government makes available to all people who are interested in weapons effects.

Mr. ROBACK. And what does it purport to convey to those people? Major STEBBINS. The goal of the document is to make available, to anyone who wants to know, blast effects, radiation effects, and other effects from weapons of different types and which burst under different conditions. It suggests what might happen to targets and people in the vicinity of targets. It gives the users many factors-for instance, they could estimate what possible levels of radiation might be distributed on the ground from weapons of various sizes, and what kinds of shielding materials they might be able to use to protect themselves. The book suffers from some defects because it attempts to be allinclusive and addresses itself to everyone.

There is probably in the 600 short pages available in the document the best single collection of weapons effects information that the Government is able to put together. It is a technical book by comparison to other documents that the lay public might pick up on this particular subject.

Yet, on the other hand, for some technical people it is inadequate, because it does not go into all the details as fully as possible.

RADIATION DECAY RATE

Mr. ROBACK. Does the Defense Atomic Support Agency have an analysis of the decay rates from radiation which is different from estimates that other agencies have?

Major STEBBINS. There have been many estimates of decay rates from radioactive fallout.

Mr. ROBACK. What would be the civil defense implications if one group estimates that radiation decays more quickly than the other? It might make a lot of difference, might it not?

Major STEBBINS. Yes, it certainly would.

Mr. ROBACK. So what does-what will the weapons effects handbook say about this problem?

Major STEBBINS. It has an extensive section on this particular problem. It attempts, without going into all the background, to present an estimate of the manner in which fallout materials will decay, which is sufficiently accurate during the times of interest, namely, when the radiation rates are high, to allow people to plan the kinds of programs necessary to provide protection from this radiation.

Mr. ROBACK. Is this the same information that was in the unrevised edition?

Major STEBBINS. It has been brought up to date. The basic concept of the rates of decay has not changed, in that, for planning purposes, the expression that the radiation levels at any time after the bomb has burst are equal to some value measured at unit time after the bomb has burst, times a power of the time that is of interest. This is the so-called t-1.2 rule.

Mr. ROBACK. That relationship has been used, has been cited for many years, and still is. You say that basically the same information is used today, you haven't modified that?

MEASUREMENT OF ACTUAL DECAY RATE ESSENTIAL

Major STEBBINS. For planning purposes, this is probably the single best, simple, numerical relationship available. The new handbook will give figures which are very closely related to that particular power law.

For planning purposes it is probably good for several hundred days after the bomb bursts.

Now, actually real fallout, as experienced in many of our tests in the past, and as we might expect to get in the future, can depart from this particular relationship rather radically. But if we try to characterize the different fallout fields that we have studied, and try to average them into one particular law which will give you something to plan with, then this is the rule to use. In the real situation one would be foolish to use the planning rule. The only way you can tell what you are actually getting is to measure it. And it is a very important part of, not only civil defense but also defense within the military, to have instruments available to actually measure the radiation rates that one is receiving at any one particular time, and to keep track of these rates over the whole period of time that one is exposed to it.

Mr. ROBACK. Are you making the point that it is important to have actual measurements because the physical law or the physical relationship that you cited may not be accurate enough to predict for protection purposes; that is, the prediction has to be squared with what happens?

Major STEBBINS. That is right. And this rule is the best planning guide that one has available today. It represents the wide variety of different conditions which have prevailed in the past. When you go

into a fallout field or take samples from it and make measurements over periods of time extending up to 200 days, as we have done in the past, we find that if you plot activity from this fallout material on a graph and attempt to fit a curve to this plot, it can often be expressed as a power law fairly accurately. Sometimes the power law is t-0.9. Sometimes it is t-2.0. It depends upon the circumstances under which the bomb was burst. It depends upon the meteorological conditions. It depends upon the soil that the bomb was burst on. There are many factors which can change the radiochemical proportions in any particular area of a fallout field. And it varies from place to place in one field from one bomb.

Mr. ROBACK. And depending on which relationship you might select and I understand there have been several different analysesit might make a difference in seeking the protection factor you might want, might it not?

Major STEBBINS. As far as the rule that you use to decide how you are going to protect yourself, I don't think that this would affect it particularly.

Mr. ROBACK. Suppose you get under one formula a much higher predicted concentration the first day than you get under another. Obviously, wouldn't that raise a question as to whether you needed a larger protection factor?

Major STEBBINS. To the extent that the formula that you use is a better representation of what you are actually going to get, then that is true, it might affect your planning in this area.

Mr. ROBACK. More important, it might determine how long you might stay in the new shelter, might it not?

Major STEBBINS. In the absence of any measurements at the time, it could influence how long you would stay in the shelter. But, of course, you really have to know how much you are getting when you first go in, or when the fallout arrives. And if you have no measurement at all, then you may be in serious trouble.

Mr. ROBACK. And it also might give you a different concept of what the residual or longtime hazard was; that is, long time in the sense that radiation persists for a long time. One prediction might show you a blank, and the other lingering radiation over a long period of time, isn't that the case?

Major STEBBINS. Any departure that one rule has from another will certainly influence it.

OCDM USE OF t-1.2 RULE

Mr. ROBACK. Mr. Brewer, does the OCDM have an official formula which it uses to advise civil defense planners as far as the decay rates of radiation are concerned?

Mr. BREWER. We use the same one.

Mr. ROBACK. The same one as whom?

Mr. BREWER. The t-1.2 rule is the planning guide available to all agencies, including the OCDM.

Mr. ROBACK. Has not OCDM made calculations which show rather marked divergence from the t-1.2?

Mr. BREWER. We are guided by the same technical data as the Defense Atomic Support Agency. And we are aware of the variations

that one will find in any measurement of a fallout field. planning purposes we use that t-1.2 rule.

But for

Mr. ROBACK. Does the Defense Atomic Support Agency have a formula which is different from that t-1.2 rule?

DEVELOPMENT OF t-1.2 RULE

Major STEBBINS. Before I answer let me attempt to summarize a little bit of the data that we have, and how one goes about attacking this particular problem.

Some years ago Way and Wigner developed a rule which attempted to define how the radiation levels from mixed fission products decays over a period of time. I believe it was in about 1942 or 1943, before a bomb had even been exploded. At that time they came up with this t-1.2 rule. The fact that it came out as a power relationship was based on a standard analytical procedure. They had some data which showed at early times there were very high rates, and at later times there were very low rates. An easy way to display their data was to put it on logarithmic paper. And as a first approximation, if you have two points on logarithmic paper and draw a line between those two points and measure the slope of the line this automatically gives a power rule; t-1.2 was their estimate at that time.

Later, when we had some actual bursts, sure enough, there were many cases where t-12 gave results which were compatible with the rate at which the radiation levels fell off in those fields. However, there were other fields and samples for which it didn't work too well. If you put the high dose rates at early times and the low dose rates at later times from these fields on logarithmic paper and draw a straight line between the points, you would say, well, it decayed at t−0.9

or t-2.0.

So we had this experimental data, and it wasn't too satisfactory in the sense that it provided an envelope much like the envelope that we heard mentioned today in discussing other matters. But we were trying to find a simple expression which would be good for planning purposes under many conditions of burst, including those we hadn't actually tested.

The Naval Radiological Defense Laboratory in San Francisco has for a long time studied the behavior of mixed fission products. In their studies they have developed rates of dosage one would expect to get from a certain kind of mixed fission products spread out on the ground in a uniform manner and over, say, a hard smooth plane, to a person 3 feet above this hard smooth plane, at certain times after the burst.

It was evident from this theoretical approach, using the known half life of various materials and the known gamma ray energies from these various materials, that the dose did not follow the t-1.2 rule, but it did diminish in time. Sometimes it was above this line, and sometimes below this line.

In the Defense Atomic Support Agency we refined this particular analytical approach by taking into account possible fractionation of the debris. By that I mean that as fallout comes down in different places it is not representative of the radioactive members of the debris

as they were originally distributed within the fireball. There are several physical phenomena which cause fractionation. As a rule in local fallout, it appears that we get a diminished amount of materials which have rare gas precursors, or which have low melting points and are consequently condensed on smaller particles that fall out farther away from the close-in fallout.

An attempt was made to subtract out these elements which might not appear in local fallout in as great a fraction as they do elsewhere in fallout, say in a worldwide fallout.

In addition, the original NRDL analysis was based on thermal fission of uranium 235. For the larger weapons the megaton weapons, it may be more appropriate to use fast fission of U238. And in addition, you will get induced activities in uranium 238 that captures the neutron without fission but rather becomes neptunium or plutonium, or uranium 237-one neutron goes in and two neutrons come out.

Major Dolan in our organization went through an analysis of this particular situation. We made available to the committee last year the results of Major Dolan's work in a paper prepared by Lieutenant Moreland which appears on page 561 of the previous hearing.

(The following additional information subsequently was received:) The analysis performed by Lieutenant Moreland was summarized by Dr. York and appears on page 521 of the previous (1960) hearings. In this summary Dr. York states: "*** The t-1,2 rule is sufficiently accurate for almost all prediction problems from less than 1 hour to approximately 100 days after the shot * * *. In any real situation one would measure the fallout field in order to establish the actual value at that time *** after a few days or weeks, it is extremely conjectural to attempt prediction of dose rates because rain, snow, wind, and other weathering effects will in almost all conceivable cases alter the decay rate* * *”

In order to improve on their previous work, NRDL prepared an additional theoretical study on the possible decay rate in a fallout field. This study used fission spectrum neutrons to produce additional fissions in U238 and took into account fractionation factors. The results of this study, along with the induced activities calculated by Major Dolan, were used in the preparation of the final decay curve which is to be presented in the revision of the "Effects of Nuclear Weapons." This final curve is remarkably close to the t-12 rule throughout the period from the 1 minute to 200 days. The difference between the two is no more than 25 percent for short periods. After 200 days, which is longer by far than the period of major concern in which lethal acute doses can be delivered, the theoretical decay rate diminishes faster than the t-12 rule. This has the effect of altering the infinity dose but not the dose of greatest significance.

To answer the original question, DASA has used several different approaches in evaluating the problem of predicting the levels of activity in a fallout field as these levels diminish through radioactive decay. Each approach has produced slightly different curves but the more refined curves differ little from the original t-1,2 rule during the times of interest.

It should be emphasized that substantial departure from the above rule should be expected in a real situation and the actual decay rates and accumulated doses should be verified by actual instrument measurements as frequently as possible.

Mr. ROBACK. In the light of these several different possibilities and several estimates by formulas, is it wise, or does it make sense, on a practical basis for the Department of Defense or the Atomic Energy Commission, or whoever has the responsibility, to lay down what are