Grid of the Gods (6 page)

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
²³⁹
U 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.