The Dawn of the Nuclear Age- Part Two

Tomorrow marks the 80th anniversary of the dropping of an atomic bomb on the Japanese city of Nagasaki. Here is both a historical and scientific look back at the dawning of the nuclear age.

Tomorrow marks the anniversary day that a second atomic bomb was exploded over an urban area. The first part of this presentation presented the physics of nuclear fission and moral implications inferred from such destructive discovery. This second part describes the engineering and consequences involved in these historical events.

Explosive Designs

To design the bombs, Robert Oppenheimer gathered a talented team of researchers and technicians at Los Alamos, New Mexico. After determining that linear acceleration would fail, they innovated an implosive lens from separate chemical explosives to simultaneously compress a sub-critical sphere of Pu-239 for achieving criticality.

Two resulting designs produced an elongated cylinder called “Little Boy” that housed uranium, and an egg-shaped spheroid called “Fat Man” that contained a plutonium ball surrounded by layers of explosives to form an implosion lens. Their respective outer casings are shown below.

Explosive yields have been quantified in metric tons of trinitrotoluene (C₆H₂(NO₂)₃CH₃), referred to as TNT. Originally used as a yellow dye, TNT also produces a shock-resistant explosive. Energy from explosions can be expressed in joules or calories, with mass measured in grams (one calorie denotes the energy to raise the temperature of one milliliter of liquid water by one degree Celsius).

In the presence of oxygen for stoichiometric reaction, the heat of combustion for TNT is 14.5 kilojoules-per-gram (kJ/g). Detonation reduces this energy release by more than half ranging between 2.673 – 6.702 kJ/g. For reference, the explosive energy from TNT is equivalent to 1.0 kcal/g or 4.184 kJ/g. A kiloton of TNT would fill a cube 27 feet 10 inches on a side.

Targeting Japan

Franklin Roosevelt initially sought to use this new weapon against Nazi Germany, but no such device was ready prior to his death. Both former and modern Japanese capitals Kyoto and Tokyo were excluded by the Truman administration as potential targets based on their cultural and political significance. Instead, American planners selected targets deemed to have specific military value. Hiroshima, located on the southern coast and western extremity of the main island of Honshu and across the northern shore of Shikoku, and having an army headquarters, thus became the first target.

Planners then chose Kokura on the northern tip of Kyushu as the second target, but cloud cover obscured the ground such that Nagasaki to the southwest on the western coast of the same island became the alternative. Niigata on Honshu north of Tokyo facing the Korea Strait served as a potential fourth target. The B-29 bombers that participated were based in Tinian, which is located among the Northern Mariana islands in the Pacific. A map shows the relative positions of these cities, along with their vectors from Tinian.

Explosive Yields

Little Boy had an estimated yield of 17 kilotonnes of TNT (71 terajoules), while Fat Man had an estimated yield of 21 kilotonnes (88 terajoules). These energies correspond to between two and three days of power produced by the Hoover dam (but released in ten micro-seconds). Later, thermonuclear explosives with nuclear fusion attained yields in the megatonne range. A rare color image below illustrates the devastation at Hiroshima.

Total destruction of these target cities extended between one and two miles in radius, as shown in the linked Reddit graphic. A survey map shows the fire (red fill) and blast damage (concentric circles) at Hiroshima.

Kokura was spared due to poor visibility, so Nagasaki received the plutonium-based Fat Man, so called because of the size of the explosive implosion geometry that was necessary to enable the fissionable material to reach critical mass. Such a complicated design had been unnecessary for the uranium-based Little Boy, but at the cost of considerably more fissile quantities being needed to achieve similar results.

Modern Muscle provides a detailed overview of the two missions and the geographies pertaining thereto. The two explosions over these urban areas extinguished an estimated one-hundred-thirty-thousand people with the initial blast. Over the next several months, radiation poisoning killed another eighty thousand persons.

Wings of Death

The Boeing B-29 Superfortress bomber that delivered both bombs also presented technological challenges. In fact, the B-29’s cost of development and production exceeded that of Project Manhattan by more than half. Featuring many innovations, the B-29 had an aerodynamically streamlined annular fuselage of 99 feet borne by thin wings stretching 141 feet and powered by a quartet of twin-row 18-piston-cylinder air-cooled radial supercharged engines.

With a range of 1,600 miles at 31,850 feet altitude, the B-29 flew at airspeeds up to 350 miles-per-hour with a bomb load of about three tons. The Wright cyclone engines delivering 2,200 horsepower each incorporated air compressors to concentrate the thin atmosphere at high altitude to augment performance.

For various reasons, a few of these aircraft had to make emergency landings in the Soviet Union. Its capabilities sufficiently impressed the Soviets to reverse engineer the B-29 design, which they designated the Tupolev Tu-4. The basic design led to a number of U.S. derivatives after the war, such as the C-97 Stratofreighter, commercial airliner Boeing 377 Stratocruiser and the KB-29 refueling tanker.

Geopolitical Aftermath

After Hiroshima’s destruction, Japanese leaders sought diplomatic intervention from the Soviets under their mutual non-aggression pact. Unbeknown to them, Stalin intended to break neutrality regarding territorial expansion for an August 15 launch by mobilizing one-and-a-half million soldiers along with tanks, artillery and aircraft to the Far East and Mongolia. The use of the first atomic bomb prompted Stalin to advance his schedule. Consequently, the Red Army invaded Japanese-held Manchuria only a few hours before “Bockscar” reached Nagasaki.

With the bomb, Japanese leadership was rudely introduced to a fiendishly destructive and previously unimagined weapon, which Roosevelt had previously warned them of, that could singly vaporize any urban area. At the same time, they had to face sudden and unexpected engagement by battle-hardened Russian troops unrenowned for their lack of mercy (with the Japanese now on the receiving end). The combined effects of devastating American technology coupled with Soviet military entry finally persuaded Emperor Hirohito to accept Allied terms, which was delivered on Sunday August 12. Despite his announcement, army leadership resisted capitulation, extolling the bitter extinction of their people in order to uphold their national honor.

Expected casualties under conventional American invasion of the home islands may have been obviated by a naval blockade that was designed to starve the empire into submission. But without imports of food and fuel, the entire populace would likely suffer.

Subsequent Research into Nuclear Synthesis

After the war, further analysis confirmed the concept of nuclear fusion of light elements, such as hydrogen into helium. This quickly led to the development of thermonuclear weapons, in which the explosive yield can be tailored and greatly increased. Further refinement of initiating mechanisms enabled volume and mass reduction to permit integration into long-range missiles, which exceeded defensive interception capabilities of target nations until only relatively recently.

In addition, greater understanding of the atomic nucleus from initial fission tests allowed astrophysics to reveal the creation of elements in the cosmos. A dozen years after the war’s conclusion, four astrophysicists introduced the “Synthesis of Elements in Stars” which explained the progression of protons and neutrons within gravitationally compressed plasma. These effects were further refined to produce the Periodic Table below, published in Science, showing the types of stars that produce specific elements.

We now know that all hydrogen and most helium atoms were formed in the Recombination aftermath of the Big Bang, and lighter elements beyond nitrogen are formed inside massive stars or from white dwarves. Heavier elements synthesize in merging neutron stars or in low mass stars, such as our sun.

Societal Implications

Humans are technological creatures. Some members conceive of new ideas, most of which fail rather miserably into dystopias for the bulk of humanity, resulting from either hubris in producing and distributing resources, or from narcissistic compulsion to command obedience in action and thought. For others who are less obsessed with what other people believe and say, such control might tinker with more effective ways to kill or disarm hostile combatants.

Occasionally, balancing aggressive competitors leads to accommodation, albeit not so often. Otto von Bismarck (c. 1870) commented “A statesman … must wait… until he hears the steps of God sounding through events, then leap up and grasp the hem of his garment.” Maybe we’ll get lucky. But history suggests otherwise.

As humans are technological creatures, a few human denizens may invent devices to ease our toil and improve our lives, or else seek to discover how observations correlate to recognizable causations. Ultimately, scientists, engineers, mathematicians, technicians, and countless others – like Prometheus – gave mankind a new type of “fire” based on fundamental characteristics of matter and energy that God Himself created. Our species merely taps into that cornucopia as commanded (Genesis 1:28). In essence, we collectively rubbed Aladdin’s lamp, and now the nuclear genie can’t be withdrawn. Eventually, we’ll make do, or perhaps die trying.

Photo Credits- Wiki Commons, I-pinming. com, Nuclear Secrecy blog, CDN History. com, C8-Alamy. com, YouTube, Warfare History Network. com and Science. org.