The great science behind the terrifying history of the atomic bomb

As much of the world celebrates the opening of the Rio Olympic Games, this weekend also marks a much darker anniversary of the moment when man used atomic science against fellow man.

It’s the 71st anniversary of the Hiroshima and Nagasaki bombings - a feat that changed the history of the world. The devastation and tragic aftermath are well known to many, but the history of how this terrifying weapon came to be is also interwoven with great scientific achievements.

Here are some facts you may not know about the Manhattan project - one of the largest scientific collaborations of the 20th century.

 

The discovery of nuclear fission was not motivated by bombs
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Nuclear fission refers to the process when the nucleus of an atom splits into smaller parts, releasing large amounts of energy. Theoretically discussed in the 1920s, it wasn’t until late 1938 when German scientists Otto Hahn and Fritz Strassmann experimented on the heavy element uranium and got unexpected results.

“Within weeks, Austrian physicist Lise Meitner and her nephew Otto Frisch explained that Hahn and Strassmann's results had resulted from the "fission" of the uranium-235 nucleus in 1939. Frisch and Meitner conducted additional experiments showing that the fission of uranium-235 resulted in a great deal of energy, making a chain reaction possible,” reads the Atomic Heritage Foundation website.

One man patented nuclear chain reactions before scientists knew how to achieve them
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Hungarian physicist Leo Szilard was struck with the notion of a nuclear chain reaction in 1933, several years before Hahn and Strassmann’s results. He went on to file a patent involving this concept in 1934.

As science historian Alex Wellerstein writes on his blog: “He had a germ of a good idea, but not the whole picture. But when the missing element came along, he was uniquely ready to see how it would complete his original idea. That’s the real story here, the real accomplishment: Szilard didn’t have to play catch-up when fission was announced, because he’d already thought a lot of this through.”

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Plutonium was discovered after the Manhattan project began
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Over the course of his career American chemist Glenn Seaborg discovered or co-discovered ten chemical elements, the first of which was plutonium, or element 94. He and his team found plutonium through bombarding uranium with deuterons - the nuclei of a hydrogen isotope called deuterium. This took place in the labs of the University of California in early 1941.

Subsequent research in the same year revealed that a version of plutonium could fission, and therefore be used as fuel for the atomic bomb. Seaborg joined the Manhattan project’s chemistry team in 1942 to help figure out a way to produce enough plutonium for a weapon.

These days, plutonium is used in the nuclear batteries of space probes, such as Pioneer and Voyager.

They built an overkill casing for the first bomb ever tested
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On 16 July, 1945, scientists successfully blew up “Gadget”, the first nuclear device ever detonated. It annihilated nearly all of the 30-metre-tall tower it was dropped from, but curiously, another item at the site survived the nuclear explosion.

This device was “Jumbo”, a huge steel cylinder over 3 metres in diameter, and more than 7 metres long. It was originally built to contain the Gadget in case it failed and the precious plutonium could then be retrieved, but ended up unused as scientists grew confident of the success of the test.

General Groves was concerned that Congress would criticise him for spending $12 million on what was essentially a white elephant, so he ordered Jumbo destroyed. However, eight 500-pound bombs only succeeded in blowing the ends of it. The remains of Jumbo can still be seen at the Trinity site,” reads the Atomic Heritage Foundation website.

 


 

For a fictional take on the famous project, check out the period drama series Manhattan on SBS On Demand.

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The two atomic bombs used were completely different
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The two bombs deployed in the fateful days of August 1945 both used nuclear fission, but were built very differently.

Little Boy was a so-called gun type bomb that housed two pieces of uranium-235 which had to be smashed into each other to combine their masses and create a chain reaction. To do this, the bomb housed some conventional explosives inside, which allowed for a quick combination of the two pieces of uranium. If this happened too slowly, the bomb wouldn’t explode, as the uranium would just slowly “fizzle”.

Fat Man was powered by synthetically made plutonium, which was not perfectly pure, and therefore didn’t allow for the ‘gun type’ design - two pieces of plutonium would start to slowly fission before smashed together, taking energy away from an actual explosion. So instead, the researchers used a mass of plutonium surrounded by conventional explosives for an ‘implosion’ method. When detonated, these would rapidly squeeze the plutonium together, causing it to reach a critical mass and fission rapidly, releasing devastating force.

Nuclear science is mostly used for good
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Nuclear technology came onto the world’s stage through the horrors of World War II, but since then scientists have harnessed their understanding of the atom for many less destructive purposes.

Amongst these the best known is the generation of electricity through nuclear power, a method that uses the same fission involved in bombs, but done in a highly controlled manner.

Understanding radioactivity - the process by which nuclei of atoms lose energy - has also helped to develop nuclear medicine, which involves not just imaging such as radiology, but also radiation treatments for diseases such as thyroid cancer.

There are also many industrial applications for radioactive atoms, including irradiation technology for preserving food, and devices that measure and analyse air pollution. Since 1957 the United Nations’ International Atomic Energy Agency has been continuously working to promote “safe, secure, and peaceful uses of nuclear science and technology.” 


Watch "The Bomb", a documentary on the history of nuclear weapons, on SBS - Monday 15th August 7.30pm.

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