Fatman Vs Little Boy?

Little Boy (The Hiroshima bomb)

Used 141 lb (64 kg) of uranium with an average enrichment of around 80%, or 112 lb (51 kg) of U-235, just about the bare-metal critical mass. (See Little Boy article for a detailed drawing.) When assembled inside its tamper/reflector of tungsten carbide, the 141 lb (64 kg) was more than twice critical mass. Before the detonation, the uranium-235 was formed into two sub-critical pieces, one of which was later fired down a gun barrel to join the other, starting the atomic explosion.

About 1% of the uranium underwent fission; the remainder, representing most of the entire wartime output of the giant factories at Oak Ridge, scattered uselessly. The inefficiency was caused by the speed with which the uncompressed fissioning uranium expanded and became sub-critical by virtue of decreased density. Despite its inefficiency, this design, because of its shape, was adapted for use in small-diameter, cylindrical artillery shells (a gun-type warhead fired from the barrel of a much larger gun). Such warheads were deployed by the United States until 1992, accounting for a significant fraction of the U-235 in the arsenal, and were some of the first weapons dismantled to comply with treaties limiting warhead numbers. The rationale for this decision was undoubtedly a combination of the lower yield and grave safety issues associated with the gun-type design.

Fat Man (The Nagasaki bomb)

Used 13.6 lb (6.2 kg, about 12 fluid ounces or 350 ml in volume) of Pu-239, which is only 39% of bare-sphere critical mass. (See Fat Man article for a detailed drawing.) Surrounded by a U-238 reflector/tamper, the pit was brought close to critical mass by the neutron-reflecting properties of the U-238. During detonation, criticality was achieved by implosion. The plutonium pit was squeezed to increase its density by simultaneous detonation of the conventional explosives placed uniformly around the pit. The explosives were detonated by multiple exploding-bridgewire detonators. It is estimated that only about 20% of the plutonium underwent fission; the rest, about 11 lb (5.0 kg), was scattered.

An implosion shock wave might be of such short duration that only a fraction of the pit is compressed at any instant as the wave passes through it.

Flash X-Ray images of the converging shock waves formed during a test of the high explosive lens system.

A pusher shell made out of low density metal—such as aluminum, beryllium, or an alloy of the two metals (aluminum being easier and safer to shape and beryllium for its high-neutron-reflective capability) —may be needed. The pusher is located between the explosive lens and the tamper. It works by reflecting some of the shock wave backwards, thereby having the effect of lengthening its duration. Fat Man used an aluminum pusher.

The key to Fat Man's greater efficiency was the inward momentum of the massive U-238 tamper (which did not undergo fission). Once the chain reaction started in the plutonium, the momentum of the implosion had to be reversed before expansion could stop the fission. By holding everything together for a few hundred nanoseconds more, the efficiency was increased.

Nuclear Weapon Design

The first nuclear weapons, though large, cumbersome and inefficient, provided the basic design building blocks of all future weapons. Here the Gadget device is prepared for the first nuclear test: Trinity.

Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three basic design types. In all three, the explosive energy of deployed devices has been derived primarily from nuclear fission, not fusion.

• Pure fission weapons were the first nuclear weapons built and have so far been the only type ever used in warfare. The active material is fissile uranium (U-235) or plutonium (Pu-239), explosively assembled into a chain-reacting critical mass by one of two methods:
• Gun assembly, in which one piece of fissile uranium is fired at a fissile uranium target at the end of the weapon, similar to firing a bullet down a gun barrel, achieving critical mass when combined.
• Implosion, in which a fissile mass of either material (U-235, Pu-239, or a combination) is surrounded by high explosives that compress the mass, resulting in criticality.

The implosion method can use either uranium or plutonium as fuel. The gun method only uses uranium. Plutonium is considered impractical for the gun method because of early triggering due to Pu-240 contamination and due to its time constant for prompt critical fission being much shorter than that of U-235.

• Fusion-boosted fission weapons improve on the implosion design. The high pressure and temperature environment at the center of an exploding fission weapon compresses and heats a mixture of tritium and deuterium gas (heavy isotopes of hydrogen). The hydrogen fuses to form helium and free neutrons. The energy release from this fusion reaction is relatively negligible, but each neutron starts a new fission chain reaction, speeding up the fission and greatly reducing the amount of fissile material that would otherwise be wasted when expansion of the fissile material stops the chain reaction. Boosting can more than double the weapon's fission energy release.

• Two-stage thermonuclear weapons are essentially a chain of fission-boosted fusion weapons, usually with only two stages in the chain. The second stage, called the "secondary," is imploded by x-ray energy from the first stage, called the "primary." This radiation implosion is much more effective than the high-explosive implosion of the primary. Consequently, the secondary can be many times more powerful than the primary, without being bigger. The secondary can be designed to maximize fusion energy release, but in most designs fusion is employed only to drive or enhance fission, as it is in the primary. More stages could be added, but the result would be a multi-megaton weapon too powerful to serve any plausible purpose. (The United States briefly deployed a three-stage 25-megaton bomb, the B41, starting in 1961. Also in 1961, the Soviet Union tested, but did not deploy, a three-stage 50–100 megaton device, Tsar Bomba.)

Pure fission weapons historically have been the first type to be built by a nation state. Large industrial states with well-developed nuclear arsenals have two-stage thermonuclear weapons, which are the most compact, scalable, and cost effective option once the necessary industrial infrastructure is built.

Most known innovations in nuclear weapon design originated in the United States, although some were later developed independently by other states; the following descriptions feature U.S. designs.

In early news accounts, pure fission weapons were called atomic bombs or A-bombs, a misnomer since the energy comes only from the nucleus of the atom. Weapons involving fusion were called hydrogen bombs or H-bombs, also a misnomer since their destructive energy comes mostly from fission. Insiders favored the terms nuclear and thermonuclear, respectively.

The term thermonuclear refers to the high temperatures required to initiate fusion. It ignores the equally important factor of pressure, which was considered secret at the time the term became current. Many nuclear weapon terms are similarly inaccurate because of their origin in a classified environment. Some are nonsense code words such as "alarm clock".

Thought Of The Day 1.0 (cont')

Type of Nuclear Weapon

There are two basic types of nuclear weapon :

The first type produces its explosive energy through nuclear fission reactions alone. Such fission weapons are commonly referred to as atomic bombs or atom bombs (abbreviated as A-bombs), though their energy comes specifically from the nucleus of the atom.

In fission weapons, a mass of fissile material (enriched uranium or plutonium) is assembled into a supercritical mass—the amount of material needed to start an exponentially growing nuclear chain reaction—either by shooting one piece of sub-critical material into another (the "gun" method) or by compressing a sub-critical sphere of material using chemical explosives to many times its original density (the "implosion" method). The latter approach is considered more sophisticated than the former and only the latter approach can be used if the fissile material is plutonium.

A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range from the equivalent of less than a ton of TNT upwards of 500,000 tons (500 kilotons) of TNT.

The second basic type of nuclear weapon produces a large amount of its energy through nuclear fusion reactions. Such fusion weapons are generally referred to as thermonuclear weapons or more colloquially as hydrogen bombs (abbreviated as H-bombs), as they rely on fusion reactions between isotopes of hydrogen (deuterium and tritium). However, all such weapons derive a significant portion, and sometimes a majority, of their energy from fission (including fission induced by neutrons from fusion reactions). Unlike fission weapons, there are no inherent limits on the energy released by thermonuclear weapons. Only six countries—United States, Russia, United Kingdom, People's Republic of China, France and India—have conducted thermonuclear weapon tests. (Whether India has detonated a "true", multi-staged thermonuclear weapon is controversial.) 

The basics of the Teller–Ulam design for a hydrogen bomb: a fission bomb uses radiation to compress and heat a separate section of fusion fuel.

Thermonuclear bombs work by using the energy of a fission bomb to compress and heat fusion fuel. In the Teller-Ulam design, which accounts for all multi-megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel (tritium, deuterium, or lithium deuteride) in proximity within a special, radiation-reflecting container. When the fission bomb is detonated, gamma and X-rays emitted first compress the fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-speed neutrons, which can then induce fission in materials not normally prone to it, such as depleted uranium.

Each of these components is known as a "stage", with the fission bomb as the "primary" and the fusion capsule as the "secondary". In large hydrogen bombs, about half of the yield, and much of the resulting nuclear fallout, comes from the final fissioning of depleted uranium.

By chaining together numerous stages with increasing amounts of fusion fuel, thermonuclear weapons can be made to an almost arbitrary yield; the largest ever detonated (the Tsar Bomba of the USSR) released an energy equivalent of over 50 million tons (50 megatons) of TNT. Most thermonuclear weapons are considerably smaller than this, due to practical constraints arising from the space and weight requirements of missile warheads.

There are other types of nuclear weapons as well. For example, a boosted fission weapon is a fission bomb which increases its explosive yield through a small amount of fusion reactions, but it is not a fusion bomb. In the boosted bomb, the neutrons produced by the fusion reactions serve primarily to increase the efficiency of the fission bomb. Some weapons are designed for special purposes; a neutron bomb is a thermonuclear weapon that yields a relatively small explosion but a relatively large amount of neutron radiation; such a device could theoretically be used to cause massive casualties while leaving infrastructure mostly intact and creating a minimal amount of fallout.

The detonation of any nuclear weapon is accompanied by a blast of neutron radiation. Surrounding a nuclear weapon with suitable materials (such as cobalt or gold) creates a weapon known as a salted bomb. This device can produce exceptionally large quantities of radioactive contamination.

Most variation in nuclear weapon design is for the purpose of achieving different yields for different situations, and in manipulating design elements to attempt to minimize weapon size. 

Thought Of The Day 1.0

Nuclear Bomb

The mushroom cloud of the atomic bombing of Nagasaki, Japan on August 9, 1945 rose some 18 kilometers (11 miles) above the bomb's hypocenter.

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission ("atomic") bomb test released the same amount of energy as approximately 20,000 tons of TNT. The first thermonuclear ("hydrogen") bomb test released the same amount of energy as approximately 10,000,000 tons of TNT.

A modern thermonuclear weapon weighing little more than a thousand kilograms (2,200 pounds) can produce an explosion comparable to the detonation of more than a billion kilograms (2.2 billion pounds) of conventional high explosive. Thus, even single small nuclear devices no larger than traditional bombs can devastate an entire city by blast, fire and radiation. Nuclear weapons are considered weapons of mass destruction, and their use and control has been a major focus of international relations policy since their debut.

In the history of warfare, only two nuclear weapons have been detonated offensively, both near the end of World War II. The first was detonated on the morning of 6 August 1945, when the United States dropped a uranium gun-type device code-named "Little Boy" on the Japanese city of Hiroshima. The second was detonated three days later when the United States dropped a plutonium implosion-type device code-named "Fat Man" on the city of Nagasaki, Japan. These two bombings resulted in the deaths of approximately 200,000 Japanese people (mostly civilians) from acute injuries sustained from the explosion. There is current debate over the atomic bombings of Hiroshima and Nagasaki.

Since the Hiroshima and Nagasaki bombings, nuclear weapons have been detonated on over two thousand occasions for testing purposes and demonstration purposes. A few states have possessed such weapons or are suspected of seeking them. The only countries known to have detonated nuclear weapons—and that acknowledge possessing such weapons—are (chronologically) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, the People's Republic of China, India, Pakistan, and North Korea. Israel is also widely believed to possess nuclear weapons, though it does not acknowledge having them.

Attention to all Nuclear Fellowship~!

From today onwards, we will try our best to entertain our readers. Updates will be done daily and i will cover different topics regarding nuclear.


Monday- We will share what we have gained in our lecture class on this day. Since the lecture ends at 7:00 pm, posts and updates will be done thereafter.

Tuesday- Same as Monday

Wednesday- General info or topic about nuclear. Maybe myth about nuclear of some of you didnt know yet.

Thursday- This will be the "Nuclear for Malaysia" drive day as the other bloggers try to convince you why Malaysia should go for Nuclear~!

Friday- Summary of what we have done from Monday till Thursday.

We are sorry for any inconvenience or technical difficulties that occurred. Thanks to all for spending a little bit of your time to our blog~!