Here, I’ll just summarize the physics of the nuclear weapon/nuclear plant.

Let’s start with an atom. An atom is made of electrons surrounding a much smaller (about 100000 times smaller than the atom) positively charged center called the nucleus. The nucleus itself is made of smaller particles, namely protons (positively charged) and neutrons (neutral particles). All of the mass (weight) of the atom is mostly stored within the nucleus. Larger the number of protons and neutrons in the atom, heavier the atom is. So Hydrogen having only a single proton and no neutron is the lightest element and most abundant element in the universe too! This is why a block of Lead or Iron is heavier compared to a block of Aluminum. Uranium is a very heavy element with 92 protons.

Now, remember the famous energy-mass equivalence principle developed by Einstein: E = mc² . This meant that if all the mass inside the nuclei can be converted to energy, you can make a bomb.

How do you convert the mass into energy? By splitting the nucleus and reducing its mass! So if one splits Uranium’s nucleus, a huge energy is bound to be released.

The splitting of the nuclei can be done by bombarding the atom with a heavy particle. Proton is a good candidate, except for its positive charge that will be repelled by the positively charged nucleus and deflect. So the physicists decided to use the neutron bombardment, which is neutral and won’t be repelled by the positive charged nucleus.

Even with the neutron bombarding, a single atom will not give enough energy to make a bomb or get useful energy out of it. The physicists learnt that it has to be a chain reaction, which means that for every neutron bombardment, there must be more neutrons released by the nucleus and these released neutrons will bombard other nuclei creating more and more neutrons in the process. This chain reaction produces LOTS of energy by multiplying the number of neutrons, enough to make a nuclear weapon or a nuclear plant.

If this chain reaction is left uncontrolled, i.e. the neutrons released are always allowed to collide with a nucleus, we have an nuclear bomb.

On the other hand, if this chain reaction is controlled by blocking the neutrons released, usually using heavy water (Hydrogen with one proton and one neutron called “Deuterium” combined with oxygen: D_2O), we have a source of nuclear energy that can be used to run your computer, phones and everything useful to you.

This addresses the physics portion of the answer to “why do we have nuclear power and weapons” question. If this question was asked from a humanitarian/existential point of view, I don’t have an answer. But, may be reading this document could help you: please read here

Thank you for your question.

Obtaining efficient ways to create energy for humans to harness is a constant challenge for engineers and scientists. When radioactive elements were discovered in the early 1900s to release a lot of energy, scientists and engineers tried to understand the phenomena of atomic energy. Many scientists researched this field, the following are two examples of discoveries that were made. Irene Joliot-Curie and Frédéric Joliot were able to artificially create radioactive elements. Otto Hahn, was a key researcher in the discovery of fission which releases a large amount of energy. By creating a large amount of energy from radioactive materials, fission is used for power plants.

Why we have nuclear weapons is a difficult question to answer. I will do my best to stay out of the politics. Because energy from fission is so powerful, many world leaders during World War II wanted to create a very powerful weapon using fission. The engineering that was developed during World War led to nuclear weapons.

Your question does lead to an important point about research. As a scientist one must understand the social implications of one’s research.

If you are interested in the history of nuclear power I recommend exploring the Nobel Prize website for Hahn, and Irene Joliot-Curie and Frédéric Joliot as well as the Wikipedia page on nuclear power.

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