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How It Works - The Atomic Bomb - Video học tiếng Anh
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How It Works - The Atomic Bomb
How It Works - The Atomic Bomb
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Субтитры (192)
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On August 6th, 1945, an American B-29 bomber flying low over the Japanese city of Hiroshima
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dropped the world’s first atomic bomb on the city’s unsuspecting inhabitants, immediately
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killing 80,000 innocent civilians.
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3 days later, a second bomb was dropped on the city of Nagasaki, killing a further 40,000
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men, women and children.
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In the aftermath of the bombs’ initial explosions, tens of thousands more people would die excruciatingly
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painful deaths due to radiation exposure.
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While the world may be familiar with the tragic story of the first use of the atomic bomb,
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we are less familiar with exactly how it works - the atomic bomb was a devastating act of
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cruelty, but also a technological marvel that would forever alter the face of war.
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The devastating bombing of Japan was enough to deter the use of nuclear weapons for at
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least a few decades, but after World War 2, increasing tension between the U.S. and Russia
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led to the Cold War, a nuclear arms race between the two world powers that saw both sides rushing
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to increase their stockpile of nuclear weapons, ostensibly as a means to deter war.
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People built bunkers in their backyards and stocked up on canned foods, schools ran nuclear
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war drills, and the world waited with bated breath for the outbreak of nuclear war and
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what felt like the imminent end of the world.
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But although the existence of nuclear weapons was common knowledge, and despite the widespread
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panic about nuclear war, few people truly understood just how an atomic bomb works.
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To understand how the atomic bomb works, we have to take a trip back to high school physics
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class to revisit the concepts of atomic structure and radioactivity.
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An atom is one of the smallest units of matter, and it is made up of 3 subatomic particles.
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The nucleus at the center of an atom is made up of protons, which are positively charged,
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and neutrons, which have a neutral charge.
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Negatively-charged electrons orbit the nucleus of an atom.
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When the ratio of protons to neutrons is 1-to-1, the atom as a whole will have a neutral charge.
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But, if the number of protons in an atom is changed, an entirely different element will
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be created.
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If the number of neutrons changes, you end up with an isotope.
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For example, the Carbon atom has 3 naturally occurring isotopes - in its common, stable
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form, Carbon-12 has 6 protons and 6 neutrons; Carbon-13 has 6 protons but 7 neutrons, and
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while rare, is still a stable element.
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Carbon-14, with its 6 protons and 8 neutrons, is both rare and unstable - or, radioactive.
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Radioactive nuclei emit particles called radiation through a process called radioactive decay,
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and it’s this process that scientists harnessed to create the powerful atomic bomb.
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There are a few different ways to destabilize a particle, but for understanding how nuclear
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bombs work, the most important processes to grasp are fission and fusion.
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Fission involves splitting the nucleus of an atom in 2, which scientists can do by bombarding
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it with free neutrons.
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As the nucleus splits, it ejects neutrons along with bursts of electromagnetic energy
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called gamma rays.
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Fusion, in contrast, involves bringing together the nucleus of two atoms to form a single
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larger one.
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This is actually the process by which our Sun produces energy.
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Through endless experimentation and a process of trial and error, scientists eventually
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discovered that uranium was the element that was most cooperative in inducing a fission
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reaction.
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The isotope Uranium-235 is one of the few materials that can be forced to undergo fission
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by bombarding its nucleus with neutrons, rather than waiting 700 million years for it to decay
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naturally.
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U-235’s nucleus will readily absorb the neutrons, become unstable and split, throwing
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off 2 or 3 new neutrons in the process.
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These new neutrons can then go on to collide with the nucleus of other U-235 atoms, starting
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a fission chain reaction.
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The splitting of the nucleus happens incredibly quickly - in the order of picoseconds, or
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0.000000000001 seconds - yepp, that’s 11 zeros!
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The scientific principles underlying the atomic bomb had been well known since Einstein’s
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days, but they wouldn’t be successfully applied and weaponized until the Second World
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War.
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In the 1930s Italian scientist Enrico Fermi successfully bombarded elements with neutrons,
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transforming them into new elements, and shortly thereafter German scientists Otto Hahn and
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Fritz Strassman were the first to fission uranium by bombarding it with neutrons, producing
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the radioactive barium isotope.
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These breakthroughs led the scientific community to wonder if it was possible to create a fission
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chain reaction that could release enormous amounts of energy that could be harnessed
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and weaponized - an idea that greatly intrigued the world’s governments, who were in the
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midst of fighting World War 2 at the time.
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In an effort to be the first to weaponize fission - and beat the Nazis to the punch
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- the U.S. government recruited the brightest minds in physics from all over the world and
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launched the secretive Manhattan Project with the goal of creating the world’s first functional
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atomic bomb.
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In 1941, scientists at Columbia University tried to initiate a chain reaction using uranium-235,
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but failed.
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Shortly thereafter, Fermi, now working for the U.S. at the University of Chicago, successfully
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achieved the world’s first controlled nuclear chain reaction in his lab underneath the school’s
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squash courts.
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Also in 1941, Berkley scientists discovered a new element - element 94 - with nuclear
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fuel potential, which they named plutonium.
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With these discoveries, the race to develop a nuclear bomb was on in earnest, and within
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just a few short years, the world’s first nuclear bombs would be used in war.
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Understanding the concept of fission was only part of the problem - figuring out how to
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weaponize it and constructing devices to harness atomic power was a whole other challenge.
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Critical mass is the minimum amount of material needed to sustain a chain reaction, so to
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harness nuclear power, the nuclear fuel has to be kept in separate subcritical masses
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that won’t support fission.
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When it’s time to detonate, the subcritical masses are brought together to form a supercritical
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mass, and free neutrons are introduced to jumpstart the fission process.
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A small pellet made of the elements polonium and beryllium serves as the neutron generator,
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and the entire reaction is confined within a dense material called a tamper, usually
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made of another uranium isotope, U-238, to reflect the neutrons back into the core and
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to slow the core’s expansion to ensure that as much fission as possible happens before
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the bomb explodes.
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Scientists developed 2 different trigger systems for the first atomic bombs.
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Little Boy, the bomb dropped on Hiroshima, was a gun-triggered bomb with a 14.5 kiloton
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yield, equal in power to 14,500 tons of TNT.
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Little Boy was 1.5% efficient, meaning that 1.5% of the material fissioned before the
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bomb exploded.
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In a gun-fired nuclear weapon, a bullet of U-235 is placed in one end of a long tube
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packed with explosives, which will fire the bullet down the tube where it collides with
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the neutron generator, initiating fission and starting the chain reaction that will
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lead to the bomb’s explosion.
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In contrast, Fat Man, the bomb that was dropped on Nagasaki, was an implosion device with
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a 23 kiloton yield and 17% efficiency - much more effective, but also much more complicated
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to make than Little Boy.
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Implosion bombs feature a sphere of radioactive U-235 as the tamper around a plutonium-239
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core.
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The entire sphere is surrounded by high explosives which, when detonated, create a shockwave
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that compresses the core and initiates the fission chain reaction.
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In the wake of World War 2, scientists recognized that fission bombs were wildly inefficient,
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and turned their attention to fusion next.
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Fusion bombs, also called thermonuclear or hydrogen bombs, rely on the hydrogen isotopes
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deuterium and tritium as fuel, and can yield up to 10,000 kilotons, making them up to 700
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times more powerful than the Little Boy fission bomb.
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Hydrogen bombs combine fission and fusion to achieve a more powerful and more efficient
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explosion.
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Within the bomb’s casing is a tamper made of U-238, which is packed with hydrogen isotope
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fuel, and surrounds a hollow rod of plutonium-239 at the core.
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An implosion fission device detonates first, compressing the fuel and causing the plutonium
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core to fission.
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The fissioning rod in turn gives off heat and pressure, which initiates fusion in the
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hydrogen isotopes and causes the bomb to explode.
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The entire process takes just 600 billionths of a second.
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Not only have the bombs themselves improved drastically, but the delivery methods have
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come a long way since World War 2.
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Philip Morrison, a former member of the Manhattan project, told Scientific American in 1995
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that "All three bombs of 1945 - the [Trinity] test bomb and the two bombs dropped on Japan
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- were more nearly improvised pieces of complex laboratory equipment than they were reliable
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weaponry."
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Today, nuclear weapons come in many forms, from ballistic missiles that can exit the
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atmosphere and travel thousands of miles before reentering and detonating; to cruise missiles,
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shorter range missiles with smaller warheads that are harder to detect and intercept; to
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a range of tactical nuclear weapons like artillery shells and land mines that can target a smaller
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area.
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Nuclear weapons are terrifying because of their immense destructive power relative to
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their size.
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The most severe damage happens at the blast’s hypocenter, or ground zero, where everything
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is immediately vaporized.
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Outward from the center, most of the damage is the result of flying debris, intense heat,
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a powerful shockwave and acute exposure to high radiation.
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Beyond the immediate blast area, death and injury can result from heat and resulting
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fires, as well as from radiation.
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The physical destruction caused by a nuclear bomb is no doubt catastrophic, but the most
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dangerous part of a nuclear bomb is the radiation and radioactive fallout.
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After the initial explosion, clouds of fine dust made of radioactive particles are carried
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away by the wind and fall back to the ground, poisoning the water supply and getting ingested
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and inhaled by people even miles away from the blast.
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We now know that radiation affects the cells in our body that readily divide, like hair
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and gut cells, bone marrow and reproductive organs, leading to nausea, vomiting and diarrhea,
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and long-term health consequences like cataracts, hair loss, loss of blood cells, and an increased
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risk of leukemia, cancer, infertility and birth defects.
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At the height of the cold war in the 1980s, scientists warned about the danger of a nuclear
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winter.
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In a worst case scenario, so many nuclear bombs could explode that great clouds of radioactive
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dust could travel high into the atmosphere, blocking out sunlight and lowering surface
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temperatures.
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This could lead to major disruptions in the food chain and mass extinctions of species
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- including humans.
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The Cold War may be over, but the threat of nuclear war is by no means gone.
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Countries around the world have signed treaties agreeing to limit their stockpile of nuclear
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weapons and prohibiting them from using them against other countries, but still, the number
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of nuclear weapons around the world continues to grow - and not all countries have agreed
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to use them responsibly.
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At least 9 countries currently have ballistic nuclear weapons, and 3 of those countries
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- the U.S., Russia and China - have weapons powerful enough to hit any target anywhere
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in the world.
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Then there’s North Korea - in 2009, they tested a nuclear bomb as powerful as the bomb
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dropped on Hiroshima, and the underground test explosion caused a magnitude 4.5 earthquake.
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There’s no doubt that nuclear warfare still presents a huge threat to world peace - not
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to mention the continuation of our species!
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If you thought this video was fascinating, be sure and check out our other videos, like
12:03
this one called “Scientists Discover 2 Billion Year Old Nuclear Reactor”, or perhaps you’ll
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like this other video.
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