Question

Define fission and write the reaction in which \(a^{235} \mathrm{U}\) nucleus is fissioned into typical products.

Short answer

Fission is the splitting of a nucleus; the reaction: \( ^{235} \text{U} + ^{1} \text{n} \rightarrow ^{141} \text{Ba} + ^{92} \text{Kr} + 3^{1} \text{n} \).

Step-by-step solution

Understanding Fission

Nuclear fission is a process where the nucleus of an atom splits into two or more smaller nuclei, along with the release of energy. This typically occurs when a heavy nucleus, such as Uranium-235, absorbs a neutron, becomes unstable, and subsequently splits.

Writing the Fission Reaction for Uranium-235

When a Uranium-235 (\( ^{235} \text{U} \)) nucleus absorbs a neutron (\( ^{1} \text{n} \)), it becomes unstable and splits into smaller nuclei, along with a few more neutrons and a large amount of energy. A typical reaction is:\[^{235}_{92} \text{U} + ^{1}_{0} \text{n} \rightarrow ^{141}_{56} \text{Ba} + ^{92}_{36} \text{Kr} + 3^{1}_{0} \text{n}\]Here, the Uranium-235 nucleus undergoes fission to produce Barium-141 (\( ^{141} \text{Ba} \)), Krypton-92 (\( ^{92} \text{Kr} \)), and three neutrons.

Analyzing the Reaction

In the reaction, the resulting nuclei (\( ^{141} \text{Ba} \) and \( ^{92} \text{Kr} \)) are called fission fragments, and the additional neutrons can go on to initiate further fission reactions. This is the basis of a chain reaction, which is exploited in nuclear reactors and atomic bombs.

Key concepts

Uranium-235: The Key to Fission

Uranium-235 is a highly significant isotope in the world of nuclear physics. It is a rare form of uranium, as most naturally occurring uranium is Uranium-238. What makes Uranium-235 special is its ability to undergo fission easily when it absorbs a neutron. This capability stems from its instability. Being a heavy nucleus, Uranium-235 is prone to splitting, especially when an extra neutron is added to it.

When a neutron collides with Uranium-235, it gets absorbed, transforming the nucleus into Uranium-236, a highly unstable isotope. This excess of energy and instability causes the uranium nucleus to split. The split results in smaller nuclei—these are typically elements like Barium and Krypton—and free neutrons. This fission process not only reshapes the nucleus but also releases a considerable amount of energy, which has practical applications in both nuclear reactors and weapons.

To summarize, Uranium-235's ability to split upon neutron absorption makes it crucial for nuclear fission. This property allows it to be harnessed as a powerful source of energy.

Understanding Fission Reactions

A fission reaction is a pivotal concept in nuclear chemistry, as it is when a heavy nucleus divides into lighter nuclei. This is not just a breakdown of particles—it's a powerful transformation accompanied by the release of energy. Let's delve into how this reaction works, using Uranium-235 as an example.

When Uranium-235 absorbs a neutron, it becomes Uranium-236, which is unstable. This instability leads the nucleus to split rapidly into smaller fragments. A typical fission reaction involving Uranium-235 is represented by the equation: \[^{235}_{92} \text{U} + ^{1}_{0} \text{n} \rightarrow ^{141}_{56} \text{Ba} + ^{92}_{36} \text{Kr} + 3^{1}_{0} \text{n}\]In this process, Uranium-236 destabilizes and splits into elements like Barium-141 and Krypton-92, along with three new neutrons. This pathway not only generates new elements but releases an enormous amount of energy due to the conversion of mass into energy, according to Einstein's equation \(E=mc^2\).

Fission reactions are the driving force behind nuclear power plants and nuclear weapons. By understanding the basic mechanics of these reactions, one can appreciate the immense energy potential stored within atomic nuclei.

Chain Reactions: A Self-Perpetuating Phenomenon

A chain reaction is a powerful sequence of events triggered by a single fission reaction, leading to a cascade of subsequent reactions. It is central to the operation of nuclear reactors and nuclear bombs. Once a Uranium-235 nucleus undergoes fission, it releases more neutrons, typically two or three. These newly liberated neutrons can strike other Uranium-235 nuclei, causing them to further split and release more neutrons and energy. This cycle of reactions continues, creating a chain reaction.

Here’s how it works:

• A neutron initiates the fission of Uranium-235.
• This fission releases additional neutrons.
• The released neutrons induce fission in other Uranium-235 nuclei.
• This process repeats, sustaining the reaction as long as sufficient fissile material is present.

The potential of a chain reaction to continue unhindered is what makes it so potent and sometimes dangerous. In a nuclear reactor, this reaction is carefully controlled to ensure a steady energy production, whereas in a nuclear weapon, it occurs in an uncontrolled and explosive manner.

The crucial factor in sustaining a chain reaction is the reproduction factor, "k," which measures how many subsequent reactions a single fission event can lead to. For a chain reaction to be sustained, the reproduction factor must be at least 1, meaning each reaction results in another one. Understanding and managing chain reactions is essential for harnessing the power of nuclear fission safely and effectively.