Additional Reading: The Nuclear Age On the 6th of August, 1945, weeks before the end of the World War II, an atomic bomb code-named "Little Boy" was detonated over the Japanese city of Hiroshima. Three days later, a second bomb, code-named "Fat Man", was dropped on the city of Nagasaki. The death and destruction wrought by these weapons were unprecedented, claiming approximately 200,000 lives and obliterating nearly every single structure within a 1.6km radius around the drop sites. While the bombings of Hiroshima and Nagasaki may have contributed to Japan's surrender, the ethicality of the use of nuclear weapons remains a hugely contentious topic today.
What is certain, however, is that the events of 1945 marked the start of the nuclear age for mankind. Nuclear energy has been heralded as one of the cleanest source of energy in terms of carbon emissions. Today, nuclear power plants provide about 6% of the world's energy and 13– 14% of the world's electricity. electricity. However, the pursuit of nuclear power is not without its costs. The Chernobyl disaster (1986), the Three Mile Island accident (1979) and the Fukushima Daiichi nuclear disaster (2011) are all reminders of the risks and hazards that nuclear power entail. Furthermore, the nuclear arms race between the United States and the Soviet Union during the Cold War period caused the number of nuclear warheads to multiply so much so that any use of the weapon in actual warfare would lead to Mutual Assured Destruction. Even in the relative peace of today, the possibility of nuclear weapons falling into the wrong hands, such as rogue states or terrorists, remains a threat to global peace and stability. In this chapter, we shall explore the science behind nuclear weapons and find out why atomic bombs are so devastatingly powerful.
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Atomic Bombs and Nuclear Weapons To understand how nuclear energy works, we shall revisit the topic on isotopes that we covered earlier. Radioactive isotopes are used to produce large amounts of energy in nuclear fission. This can be done in a controlled way in a nuclei reactor. One common fuel used is an isotope of uranium, uranium-235. In the reactor, the uranium atoms are bombarded with neutrons. When the neutron hits a uranium nucleus, the nucleus breaks up into two smaller nuclei. This is called nuclear fission. An exampl exa mple e is i s show s hown. n.
Mass Defect and Binding energy The mass of the nucleus is about 1 percent smaller than the mass of its individual protons and neutrons. This difference is called the mass defect. defect. The mass defect arises from the energy released when the nucleons (protons and neutrons) bind together to form the nucleus. This energy is called the binding energy. energy. The binding energy determines which nuclei are stable and how much energy is released in a nuclear reaction. The hydrogen-2 nucleus, for example, composed of one proton and one neutron, can be separated completely by supplying 2.23 million electron volts (MeV)* of energy. Conversely, when a slowly moving neutron and proton combine to form a hydrogen-2 nucleus, 2.23 MeV are liberated. *1eV = 1.602!10
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Einstein's formula: E = mc 2 The mass defect and binding energy are related by the formula E = mc 2. In 1905, Albert Einstein developed the special theory of relativity. One of the implications of this theory was that matter and energy are interchangeable with one another. This equation states, a mass (m) can be converted into an amount of energy (E), where c is the speed of light. #
Because the speed of light is a large number and thus c2 is huge, a small amount of matter can be converted into a tremendous amount of energy. energy . This equation is the key to the power of nuclear weapons and nuclear reactors. During fission, more neutrons are produced. These neutrons cause fission in other uranium atoms. This is repeated over and over again. This repeated process is called a chain reaction. A lot of heat energy en ergy is produced p roduced in a nuclear nu clear fission fissio n chain reaction. In a nuclear reactor, this heat energy is used to produce steam which is then used to drive a turbine and dynamo to generate electricity. When the chain reaction in nuclear fission is allowed to get out of control, an explosion can occur. This is done deliberately in explosions produced by nuclear weapons. The explosion is produced by uncontrolled fission of uranium-235 or plutonium-239. Consequences of Nuclear Weapon As we see earlier, a small amount of matter can be converted converte d into a tremendous tremend ous amount of energy in a nuclear reaction. Therefore nuclear weapon is far more powerful than any conventional weapon. The atomic bomb dropped on Hiroshima, the “Little Boy”, released between 54 and 75 TJ (Tera- = 1012) of energy, which is equivalent to 13 to 18 kilotons of TNT. The modern nuclear weapon is even more devastating, as a weapon weighing a little more than 1,100kg is capable of releasing energy equivalent to more than 1.2 Megatons of TNT. Health Risks Most of the immediate damage caused by nuclear weapons is due to the energy released. This takes the form of intense heat as well as shock waves which destroys both living things and structures. There are many long-term health effects of nuclear weapons as well. Radiation and radioactive fallout affect those cells in the body that actively divide (hair, intestine, bone marrow, reproductive organs). Some of the resulting health conditions include: • • • •
Nausea, vomiting and diarrhea Cataracts Hair loss Loss of blood cells
These conditions often increase the risk of leukemia, cancer, infertility infertility and birth defects.
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References http://www.atomicarchive.com/Phys http://www.atomicarchive.com/Physics/Physics1.s ics/Physics1.shtml html http://energyfromthorium.com/2010/08/06/loveswu1/ http://science.howstuffworks.com/nucl http://science.howstuffworks.com/nuclear-bomb8.htm ear-bomb8.htm http://en.wikipedia.org/wiki/Nuclear_weapon Picture references en.wikipedia.org (3), p3 archives.govt.nz, p3 en.wikipedia.org, p15 craighill.net, craighill.net, p41
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