20-08-2012, 05:06 PM
Nuclear Technology & its Application
[attachment=32224]
DISCOVERY
On January 16, 1939, Niels Bohr of Copenhagen, Denmark, arrived in the United States to spend several months in Princeton, New Jersey, and was particularly anxious to discuss some abstract problems with Albert Einstein. (Four years later Bohr was to escape to Sweden from Nazi-occupied Denmark in a small boat, along with thousands of other Danish Jews, in large scale operation.) Just before Bohr left Denmark, two of his colleagues, Otto Robert Frisch and Lise Meitner (both refugees from Germany), had told him their guess that the absorption of a neutron by a uranium nucleus sometimes caused that nucleus to split into approximately equal parts with the release of enormous quantities of energy, a process that they dubbed "nuclear fission" (fission, as previously used up to this point, was a term which was borrowed from biology, where it was and is used to describe the splitting of one living cell into two).
NUCLEAR WEAPONS
A nuclear weapon is a weapon which derives its
destructive force from nuclear reactions of either
nuclear fission or the more powerful fusion. As a
result, even a nuclear weapon with a relatively small
yield is significantly more powerful than the largest
conventional explosives, and a single weapon is
capable of destroying an entire city.
In the history of warfare, nuclear weapons have
been used only twice, both during the closing days
of World War II. The first event occurred on the
morning of August 6, 1945, when the United States
dropped a uranium gun-type device code-named
"Little Boy" on the Japanese city of Hiroshima.
The second event occurred three days later when a
plutonium implosion-type device code-named
"Fat Man" was dropped on the city of Nagasaki. The use
of these weapons, which resulted in the immediate deaths
of around 100,000 to 200,000 individuals .
CRITICAL MASS
A mass of fissile material is called critical when it is capable of a sustained chain reaction, which depends upon the size, shape and purity of the material as well as what surrounds the material. A numerical measure of whether a mass is critical or not is available as the neutron multiplication factor, k, where
k = f − l
where f is the average number of neutrons released per fission event and l is the average number of neutrons lost by either leaving the system or being captured in a non-fission event. When k = 1 the mass is critical, k < 1 is subcritical and k > 1 is supercritical. A fission bomb works by rapidly changing a subcritical mass of fissile material into a supercritical assembly, causing a chain reaction which rapidly releases large amounts of energy.
Direct effects
Nuclear weapons emit large amounts of electromagnetic radiation as visible, infrared, and ultraviolet light. The chief hazards are burns and eye injuries. On clear days, these injuries can occur well beyond blast ranges. The light is so powerful that it can start fires that spread rapidly in the debris left by a blast. The range of thermal effects increases markedly with weapon yield. Thermal radiation accounts for between 35-45% of the energy released in the explosion, depending on the yield of the device.
[attachment=32224]
DISCOVERY
On January 16, 1939, Niels Bohr of Copenhagen, Denmark, arrived in the United States to spend several months in Princeton, New Jersey, and was particularly anxious to discuss some abstract problems with Albert Einstein. (Four years later Bohr was to escape to Sweden from Nazi-occupied Denmark in a small boat, along with thousands of other Danish Jews, in large scale operation.) Just before Bohr left Denmark, two of his colleagues, Otto Robert Frisch and Lise Meitner (both refugees from Germany), had told him their guess that the absorption of a neutron by a uranium nucleus sometimes caused that nucleus to split into approximately equal parts with the release of enormous quantities of energy, a process that they dubbed "nuclear fission" (fission, as previously used up to this point, was a term which was borrowed from biology, where it was and is used to describe the splitting of one living cell into two).
NUCLEAR WEAPONS
A nuclear weapon is a weapon which derives its
destructive force from nuclear reactions of either
nuclear fission or the more powerful fusion. As a
result, even a nuclear weapon with a relatively small
yield is significantly more powerful than the largest
conventional explosives, and a single weapon is
capable of destroying an entire city.
In the history of warfare, nuclear weapons have
been used only twice, both during the closing days
of World War II. The first event occurred on the
morning of August 6, 1945, when the United States
dropped a uranium gun-type device code-named
"Little Boy" on the Japanese city of Hiroshima.
The second event occurred three days later when a
plutonium implosion-type device code-named
"Fat Man" was dropped on the city of Nagasaki. The use
of these weapons, which resulted in the immediate deaths
of around 100,000 to 200,000 individuals .
CRITICAL MASS
A mass of fissile material is called critical when it is capable of a sustained chain reaction, which depends upon the size, shape and purity of the material as well as what surrounds the material. A numerical measure of whether a mass is critical or not is available as the neutron multiplication factor, k, where
k = f − l
where f is the average number of neutrons released per fission event and l is the average number of neutrons lost by either leaving the system or being captured in a non-fission event. When k = 1 the mass is critical, k < 1 is subcritical and k > 1 is supercritical. A fission bomb works by rapidly changing a subcritical mass of fissile material into a supercritical assembly, causing a chain reaction which rapidly releases large amounts of energy.
Direct effects
Nuclear weapons emit large amounts of electromagnetic radiation as visible, infrared, and ultraviolet light. The chief hazards are burns and eye injuries. On clear days, these injuries can occur well beyond blast ranges. The light is so powerful that it can start fires that spread rapidly in the debris left by a blast. The range of thermal effects increases markedly with weapon yield. Thermal radiation accounts for between 35-45% of the energy released in the explosion, depending on the yield of the device.