5) A mere eighty generations of fissioning atoms after this — which has all occurred in a “few millionths of a second”09 — X-rays from the fission fireball at the center of the primary (hotter than the center of the Sun!) have escaped beyond the assembled mass at the speed of light, and have traveled down the cylinder around the secondary and also shown over the entire interior surface of the casing. These x- rays caused the polyethylene lining to instantly heat to a plasma, which reflected the x-rays back on to the uranium casing of the secondary, which, course, liquified and vaporized the uranium as it was being driven inward by the sheer pressure of x-ray radiation;10
Simplified Schematic of a Three Stage Fission-Fusion-Fission Hydrogen Bomb first tested in the “Mike”
6) As this liquifying and vaporizing uranium is being crushed and relentlessly compressed around the cylinder of cryogenically cooled liquid deuterium, that deuterium itself begins to be intensely pressurized as its temperature rises within microseconds to fusion energies;11
7) All this extremely hot witches’ brew then further compresses around the uranium-238 fission booster, which, under the extreme pressures and radiations of x-rays and thermal neutrons, also fissions, spitting even more x-rays and neutrons into the whole recipe. These x-rays further heat the compressing deuterium, pushing its nuclei past the barriers of electrostatic repulsion and causing them to fuse together;12
8) At this juncture, according to hydrogen bomb historian Richard Rhodes, three different kinds of fusion reaction occurred, and here, we begin to observe the beginnings of a “problem”:
a) According to Rhodes, some of these deuterium nuclei “fused to form a helium nucleus — an alpha particle — with the release of a neutron, the alpha and the neutron sharing an energy of 3.27 MeV.”13 This neutron then shoots “through the mass of fusing deuterons”14 and escapes, while the positively charged alpha particle adds its own energy to the mass of heating deuterons, further heating it;15
b) But there is another reaction that occurs. Some deuterons fuse to form a tritium nucleus — that is, a hydrogen isotope’s nucleus consisting of one proton and two neutrons — releasing a free proton which in turn dumps its energy into the heating mass of deuterons, with “the triton and the proton sharing 4.03 MeV;”16
Simplified Schematic of a Three Stage Fission-Fusion-Fission Hydrogen Bomb first tested in the “Mike”
c) The third reaction that can occur is when a tritium nucleus fuses with one of deuterium to form yet another alpha particle — a helium nucleus of two protons and two neutrons — plus a thermal neutron that, among them, share an energy of 17.59 MeV;17
(We will return to the “problem” posed by this account in a moment. For the present, it suffices to note simply that there may be a problem here.)
9) The thermal neutron from the tritium-deuterium reaction described in point 8)a) above has an energy of 14 MeV, and this neutron then escapes the compressing deuterium plasma and collides with the uranium-238 “fission booster” in the secondary, which then itself begins to fission under this intense thermal or high energy neutron bombardment, and this of course floods even more intense x-ray radiation into the deuterium plasma.18 In effect, this means that the deuterium plasma is trapped “between two violent walls of heat and pressure.”19 This creates three further reactions:
a) As neutrons are banging around in this witches’ brew, some of the deuterium nuclei will capture them, transforming from deuterium (with one proton and one neutron) into tritium (with one proton and two neutrons). This tritium then fuses with other tritium, which produces a helium nucleus or an alpha particle (two protons and two neutrons) plus two free thermal neutrons, all of which share an energy of 11.27 MeV;20
b) Some of this deuterium-created helium then in turn fuses with deuterium and creates heavy helium (a helium nucleus with an extra neutron) plus a “highly energetic proton;”21
c) Some of the fusing deuterons breed tritium plus a proton, with further release of energy in the form of more radiation, and further fueling the force of “Mike’s” explosion.22
All of this led to a colossal detonation, the largest at that point in time that had ever been seen on the Earth:
Momentarily, the huge Mike fireball created every element that the universe had ever assembled and bred artificial elements as well. “In nanoseconds,” writes the physicist Philip Morrison, “uranium nuclei captured neutron upon neutron to form isotopes in measurable amounts all the way from 239U up to mass number 255. Those quickly decayed, to produce a swath of transuranic species from uranium up to element 100, first isolated from that bomb debris and named Fermium.”
Swirling and boiling, glowing purplish with gamma-ionized light, the expanding fireball began to rise, becoming a burning mushroom cloud balanced on a wide, dirty stem with a curtain of water around its base that slowly fell back into the sea. The wings of the B-36 orbiting fifteen miles from ground zero at forty thousand feet heated ninety-three degrees almost instantly. In a minute and a half, the enlarging fireball cloud reached 57,000 feet; in two and a half minutes… the cloud passed 100,000 feet. The shock wave announced itself with a sharp report followed by a long thunder of broken rumbling. After five minutes, the cloud splashed against the stratopause and began to spread out, its top cresting at twenty-seven miles, its stem eight miles across…
… The explosion vaporized and lifted into the air some eighty million tons of solid material that would fall out around the world… It stripped animals and vegetation from the surrounding islands and flashed birds to cinders in midair.23
That was not all:
Fireball measurements and subsequent radiochemistry put the Mike yield at 10.4 megatons — This, of course, is our small “problem,” for this, it will be recalled, was almost double the most likely predicted yield for the “device;” the scientific term for it would be: “Woops!”
— the first megaton-yield thermonuclear explosion on earth. Its neutron density was ten million times greater than a supernova, Cowan remarks, making it “more impressive in that respect than a star.” The Little Boy uranium gun that destroyed Hiroshima was a thousand times less powerful. Mike’s fireball alone would have engulfed Manhattan; its blast would have obliterated all New York City’s five boroughs. More than 75 percent of Mike’s yield, about eight megatons, came from the fission of the big U238 pusher around the secondary; in that sense it was less a thermonuclear than a big, dirty fission bomb.24
Our “little” problem has now grown into a monster, for where did all this extra energy –some four to six megatons over the predicted likely yield — come from?
One answer came immediately: it came simply from the efficiency of the reaction burns themselves.
As we shall see, this does not really solve the problem, but rather, only amplifies it, for as we shall now see, the problem only became more acute in the next series of thermonuclear “miscalculations…”
B. The Designs of “Shrimp” and “Runt”: The Second and Third “Woops!”
All this would not have been so bad, except for the fact that it happened again, and with a vengeance, during America’s first test of an actual deliverable hydrogen bomb, the “Castle Bravo” test of March 1, 1954, and for yet a third time during the “Castle Romeo” test a few days later, on March 27, 1954. Once again, the bombs, when fired, ran far away from their predicted pre-test yields.
As we saw in our survey of the “Mike” test, the actual device used liquid cooled deuterium as the fusion fuel in its secondary, making the device not only large, but giving it a weight of 62 tons, making it simply impractical as a deliverable weapon of any sort. The actual reason for the test was simply to determine if the various stages for a hydrogen bomb could actually be engineered to work in the sequence outlined in the previous pages. However, once the shot had proven that the basic design principles of staged reactions were sound — never mind that “little problem” that the actual yield almost doubled the likely predicted yield — design of a solid-fueled,
deliverable weapon began in earnest, and the first of these, a device named “Shrimp” was detonated during the “Castle Bravo” test of March 1, 1954, the test that soon became infamous around the world.
The “Shrimp” device used a mixture of lithium-6 and deuterium — lithium deuteride — as the main fusion fuel in its secondary. Approximately 40 percent of the lithium in in this lithium deuteride was composed of the lithium-6 isotope, while the other 60 percent was composed of the more common and stable lithium-7. The problem was, the predicted yield for the device was about 6 megatons, plus or minus 2 megatons. In other words, the expected yield was 4–8 megatons. Yet, when it was actually detonated, the explosion quickly went out of control, and ran away to 15 megatons, almost 4 times the low end of the predicted yield, and almost double the high end!25
The Castle Bravo Dry-Fueled Deliverable “Shrimp” Device, with a Human Silhouette Superimposed to show approximate size. Compare with the much larger “Mike” device on page 3.
This “slight miscalculation” was not without its consequences and repercussions, for
The Bravo test created the worst radiological disaster in US history. Due to failures in forecasting and analyzing weather patterns, failure to postpone the test following unfavorable changes in the weather, and combined with the unexpectedly high yield and the failure to conduct pre-test evacuations as a precaution, the Marshallese Islanders on Rongelap, Ailinginae, and Utirik atolls were blanketed with the fallout plume, as were U.S. servicemen stationed on Rongerik.
Within 15 minutes after the test radiation levels began climbing on Eneu Island, site of the test control bunker, which was supposed to be upwind from the test and thus immune to fallout. An hour after the shot the level had reached 40 (Rads per hour), and personnel had to retreat from the control room to the most heavily shielded room of the bunker until they could be rescued 11 hours later.
An hour after the shot Navy ships 30 miles south of Bikini found themselves being dusted with fallout with deck radiation levels rising to 5 (Rads per hour). Navy personnel were forced to retreat below decks and the ships retreated farther from the atoll.
As the fallout drifted east U.S. evacuation efforts lagged behind the plume. At Rongerik, 133 (nautical miles) from ground zero, 28 U.S. personnel manning a weather station were evacuated on 2 March but not before receiving significant exposures. Evacuations of the 154 Marshallese Islanders only 100 (Nautical miles) from the shot did not begin until the morning of 3 March. Radiation safety personnel computed that the islanders received a whole-body radiation dose of 175 rad on Rongelap, 69 rad on Ailininae, and 14 rad on Utirik.26
But that was not the end of the fallout — pun intended — from the event.
The Japanese fishing vessel Daigo Fukuryu (Fifth Lucky Dragon) was also heavily contaminated, with the 23 crewmen receiving exposures of 300 R, one of whom later died — apparently from complications. This incident created an international uproar, and a diplomatic crisis with Japan.27
One cannot blame the Japanese government for being more than a little angry, because the “Castle Bravo” shot meant, in effect, that it was the third time America had nuked Japan, and this time, the two countries were not even at war and the victims were innocent fishermen trying to make a living!
After the dramatic and completely unexpected yield of “Castle Bravo,” a yield at the minimum almost double of what was expected, the United States abandoned its fire control bunkers on Bikini atoll, opting in the future for distant remote control firing, and the exclusion zones around test areas was increased to 570,00 square miles, or a circle 850 miles across!28
The Castle Bravo Test From About Fifty Miles Away, approximately two and a half minutes after the explosion.
The fireball of the “Castle Bravo” test “expanded to nearly four miles in diameter. It engulfed its 7,500 foot diagnostic pipe array all the way out to the earth-banked instrument bunker, which barely survived. It trapped people in experiment bunkers well outside the expected limits of its effects and menaced task force ships far out at sea.”29 To put it mildly, the “Shrimp” bomb was a runaway monster, and left the physicists and engineers dumbfounded, even as they were staring at their visible bones in their hands, even through their tightly-shut and goggled eyes.
While the U.S. military were scrambling to rescue the islanders and service personnel endangered by the test shot, a red-faced State Department was trying to explain the “curious results” to the angry governments of the region, not the least of which was Japan. How could such a drastic miscalculation have happened? What had gone wrong, or from the weapons designers’ point of view, what had gone so incredibly right?
The crisis had barely abated, when on March 27, 1954, the United States once again rolled the thermonuclear dice in the “Castle Romeo” test, and once again achieved some rather unexpected results. Its original predicted yield, prior to the spectacular “Bravo” success (or, depending on how one wants to view it, failure), was for a yield of 4 megatons, with outside limits being 1.5 to 7 megatons.30 In the wake of the “Bravo” test, however, scientists quickly revised their yield predictions, and now calculated a yield of between 1.5 to 15 megatons with the likely yield being 8 megatons!31 When fired, the “Castle Romeo” device, a bomb codenamed “Runt I” once again “ran away,” yielding an explosion of 11 megatons. Of course, this fell well within the revised predicted yield, but only because the predicted yield was of such a wide margin of error, as compared with the pre-”Bravo” yield of 4 megatons with outer limits of 1.5–7 megatons!
Once again, our little problem has returned, the problem that began with “Mike,” and continued with “Runt I”: where was all this extra energy coming from?
1. An Interesting Story
More light can be shed on that question by a glance at the tables for the pre- and post-Bravo predicted yields for the Castle series of nuclear tests, for these tables tell an interesting story.
The Castle series of tests was to have consisted of eight shots, designated Bravo, Union, Yankee, Echo, Nectar, Romeo, and Koon, respectively. The following table gives the names of the tests, the name of the device tested, and the pre-Bravo predicted yields expected for each:
Table of Pre-Bravo Predicted Yields for the Castle Series of Nuclear Tests32
But in the wake of the “Bravo” success as a firing, and its failure as an international incident, the figures for all remaining tests were re-calculated, and an explanation for its run-away success was found, but in that explanation, a new, and terrible, mystery surfaces, as we shall see.
2. The Standard Explanation for “Castle Bravo” and “Castle Romeo”
It will be recalled from our previous description of the “Bravo” test’s “Shrimp” device that approximately 60 percent of the lithium mixture of the lithium deuteride was ordinary, stable, everyday common lithium-7. And therein lay the explanation (at least, as far as we have been told):
The room-temperature Shrimp device used lithium enriched to 40 percent lithium 6; it weighed a relatively portable 23,500 pounds and had been designed to fit the bomb bay of a B-47 when it was weaponized. It was expected to yield about five megatons, but the group at Los Alamos that had measured lithium fusion cross sections had used a technique that missed an important fusion reaction in lithium 7, the other 60 percent of the Shrimp lithium fuel component. “They really didn’t know,” Harold Agnew explains, “that with lithium 7 there was an n, 2n reaction (i.e., one neutron entering a lithium nucleus knocked two neutrons out). They missed it entirely. That is why Shrimp went like gangbusters.” Bravo exploded with a yield of fifteen megatons, the largest-yield thermonuclear device the US ever tested.33
Woops.
Certainly the lithium-7 reactions do explain most of the reason why such an inordinately high yield was achieved, and do so within acceptable margins of error.
Or do they?
Let us do a bit of detective work concerning this lithium-7 explanation. We first observe that the explanation of the e
xtra energy achieved for those tests on the basis of the fusion of ordinary lithium-7 might be true in the cases of those tests, except for one important problem: the original H-bomb test, “Mike,” was not fueled by lithium reactions at all, but solely by the fusion of deuterium reactions along with the fission reactions in the primary and secondary. Nowhere in standard thermonuclear reactions is there a reaction that forms lithium-7 from various reactions of deuterium, either with itself or with other products within its family of reactions!34 So where did “Mike’s” extra energy come from?
We are told that the lithium-7 reaction accounted for this extra “boost” in the reaction yield, but as we have already seen, in the overwhelming case of lithium-7 reactions, the resulting products will allow only one component, tritium, to continue fusion reactions, and those reactions form a comparatively small percentage of normal fusion reactions.
To put it bluntly, and succinctly, though it would appear that while the lithium-7 explanation accounts for most of the extra yield of these two devices, it is unlikely that it accounts for all of it. Why are we reasonably confident of this? Because, once again, the original hydrogen bomb, “Mike,” contained no lithium-6 or lithium-7, and yet it too “ran away”! Its reactions would have been confined to reactions not involving lithium-7, and these would have had to have burned very efficiently to achieve its actual yield.
Grid of the Gods Page 4