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Science of Nuclear Weapons

Introduction

Nuclear weapons are commonly referred to as the most powerful weapon known to and used by humans. The use, proliferation, and subsequent anti-proliferation treaties of nuclear weapons are frequently debated topics. One aspect of nuclear weapons that is not frequently debated would be the fundamental science of these weapons. It is known to many that nuclear weapons, in practice, use radioactive materials to create a large fireball for the purpose of destruction. What is unknown to many is how the fireball is generated.

Pre-History of Nuclear Weapons

Before the 1900s, it was theorized that not all elements hold the same intrinsic properties and that some hold wildly different properties than other elements. One element drew much attention to itself because of its unique properties, Uranium. Marie Curie managed to discover and study a new element, Radium, when studying uranium. This discovery was perplexing, as it indicated that atoms could decompose into new elements. This would continue to puzzle scientists for nearly the following 30 years.

In the early 1930's, it had been established that heavier elements such as uranium had the potential to decay into two lighter elements, an alpha particle, and a significant amount of energy. The new goal of scientists was to determine if this decay could be initiated. In 1933, Enrico Fermi determined that this could be initiated by firing a neutron into an atom of uranium, which would push the atom over the figurative edge to force a decay. The new question was whether the initiation of one decay would lead to another, in a sort of chain reaction.

In 1939, it was known that a chain reaction was possible. Notable scientists such as Enrico Fermi, a pioneer in nuclear weapons research, agreed that such an event was indeed possible. This meant that if enough Uranium was gathered, then it is conceivable that the initiation of one decay would set off numerous other decays in the sample of Uranium. This would lead to a significant amount of energy being released in a short manner of time, leading to an explosion.

First Practical Application

After determining that a chain reaction was possible, the route to building a functioning weapon started with acquiring enough Uranium to achieve a Critical mass. A critical mass is the amount of Uranium that must be collected into a single object such that a chain reaction can sustain itself. Not any isotope of Uranium was acceptable, as it needed to be Uranium-235 in a concentration of at least 70% for a chain reaction to be self-sustaining. This is due to the fact that of the two most common isotopes of Uranium, Uranium-235 and Uranium-238, only Uranium 235 was capable of achieving a chain reaction. The problem then arose of acquiring enough Uranium 235, as it only occurs in a percentage of 0.7% naturally occurring Uranium. To acquire an amount of Uranium necessary for a critical mass, methods such as mass spectroscopy and gas diffusion were used to separate the lighter Uranium 235 from its counterpart Uranium 238. These methods were slow and expensive, costing the equivalent of billions of United States dollars in the year 2021. Once the critical mass had been gathered, the primary method for creating a functioning bomb was to fire a Uranium 235 "slug" into a receiving sphere of Uranium 235 to instantaneously create a critical mass.

An alternative route was also considered for acquiring a critical mass. This method involved using Plutonium, a byproduct of producing Uranium, as the new material to be made into a critical mass. This method was comparatively faster than the mass spectroscopy and gas diffusion methods but was just as expensive. It was possible for a weapon to be made from Plutonium in a fraction of the time that it would take to gather enough Uranium 235 to make a Uranium weapon. The drawback to this method is that for a critical mass to be achieved, the plutonium could not simply be brought together into one piece. Instead, this method involved compressing a sphere of Plutonium into a small enough space to initiate a chain reaction. The compression was initiated by the simultaneous detonation of explosives surrounding a Plutonium core.

Of the two routes to making a functioning weapon, the scientists developing the weapon were certain of the success of the Uranium weapon but were unsure of the success of the Plutonium weapon. This led to the testing of the first nuclear weapon.

Testing

The first nuclear test to occur was performed on July 4th, 1945. This test was the detonation of what was known as "The Gadget", a plutonium core nuclear weapon. The test was meant to determine if the implosion design of the Plutonium bomb would work in practice. A concern in this test was whether the bomb in question had the potential to ignite the atmosphere itself on fire. Extensive calculations and findings on the potential chemistry of a nuclear reaction in the air and the energy it would release were found and the scientists at the test site were confident that the atmosphere was safe from ignition. The test proceeded, yielded the largest explosion ever known to man at the time. With this, the nuclear bomb had become a reality.

Fission to Fusion

Years after the testing and use of nuclear weapons by the United States against Japan, nuclear weapon technology had stemmed out into a new branch of nuclear physics. The previous bomb types relied on the splitting of heavier atoms to release energy; a process known as Fission. As science progressed and technology improved, the possibility of a new type of nuclear weapon was conceived, one that relies on Nuclear fusion. The process of fusion involves combining two light elements such as hydrogen to produce a single heavier element such a helium. This process also releases energy as the binding forces within and between atoms are overcome. This type of weapon would involve a traditional Plutonium or Uranium core and would then encase the core in a chamber of hydrogen. As the Uranium or Plutonium is detonated, the temperatures reached would mimic that of a star such as the sun, allowing the hydrogen atoms to break the nuclear bonds keeping them separate and would fuse. This would add dramatically to the power of a nuclear weapon, and this new power does not have a conceivable limit. As the hydrogen increases the yield of the nuclear weapon, the process of adding layers of hydrogen to the nuclear weapon could theoretically be repeated indefinitely. The only limits on the size of such a nuclear bomb would be available resources and the ability to transport such a weapon.