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Kabir Punjwani

The Science Behind the First Nuclear Weapon

The Manhattan project was designed to create the first nuclear weapon in all of history.

The project included many great scientists and it was headed by Robert Oppenheimer.

Two bombs were being prepared – a uranium-based bomb called 'Little Boy’ and a plutonium-based bomb called ‘The Fat Man’.


Nuclear weapons are based on the concept of nuclear fission. Nuclear fission is the division of a nucleus of an atom (usually a large nucleus) with the bombardment of neutrons on that atom. It’s when an unstable atom splits into 2 or more atoms which are more stable in nature.

In the making of the atomic bomb, uranium with the atomic weight of 235 is used and not 238 because uranium-235 is a more fissile element. Meaning uranium-238 can undergo the nuclear fission only when fast moving neutrons are bombarded at them however, uranium-235 can undergo the fission even with slow moving neutrons.


When uranium-235 is bombarded with 1 neutron with a mass of 1 a.m.u and no charge, it changes into uranium-236, which then splits into barium-144 and krypton-89 and releases 3 neutrons and a tremendous amount of energy.


We have already learnt about the fission of uranium-235 but now let’s calculate how much energy is actually released.


The difference in the mass of the products and the original reactants is 0.20 a.m.u.

The mass lost is released as energy which we come to know from Einstein’s general relativity theorem. According to General relativity theorem ( e=mc2 ), 1 atomic mass unit = 931 Mega electron volt.

Therefore, the total energy released is 931 x 0.20 = 190 MeV.

Thus, in the fission of 1 uranium-235 nucleus nearly 190 MeV energy is released.

However, when the uranium-235 undergoes nuclear fission, the neutrons released by it can cause fission in the other uranium nucleus also. This leads to a chain of nuclear fission. However, this chain reaction is uncontrolled and it can release a huge amount of energy which can be very harmful. This uncontrolled chain reaction of uranium-235 was used in the making of the atomic bomb.


Nuclear weapons are very harmful and their impact affects a large part of land for many years. For those along with their families who survive the initial blast, it is a reminder of the tragedy as they are often affected for generations due to the sheer amount of radiation given out by an atomic bomb. As of now, The United Nations Treaty on the Prohibition of Nuclear Weapons (TPNW) makes it unlawful to possess, develop, deploy, test, use or threaten to use nuclear weapons.


'Little Boy'

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