Question

Identify the false statement about nuclear fission. (a) Nuclear fission is induced by bombarding a U-235 sample with beta particles. (b) Nuclear fission is the splitting of a heavy element into lighter elements. (c) Mass is converted to energy in nuclear fission. (d) Nuclear fission releases huge amounts of energy compared to chemical reactions. (c) Nudear fission can cause a chain reaction because additional neutrons are produced with each fission of a nucleus.

Short answer

Statement (a) is false.

Step-by-step solution

Understanding Nuclear Fission

Nuclear fission is a nuclear reaction where a heavy nucleus splits into smaller nuclei, along with free neutrons and other byproducts. It usually initiates through the absorption of a neutron, leading to a chain reaction if conditions allow.

Analyze Statement (a)

Statement (a) claims that nuclear fission is induced by beta particles. Beta particles are a form of radiation consisting of high-energy, high-speed electrons or positrons. Fission is actually induced by neutrons, not beta particles, so this statement is incorrect.

Analyze Statement (b)

Statement (b) describes fission as the splitting of a heavy element into lighter elements. This is a correct description of nuclear fission, as it involves breaking apart a heavy nucleus like U-235 into lighter fragments.

Analyze Statement (c)

Statement (c) suggests that mass is converted to energy during nuclear fission. According to Einstein's equation, E=mc², a small amount of mass is indeed converted into a large amount of energy during fission, making this statement true.

Analyze Statement (d)

Statement (d) claims that nuclear fission releases large amounts of energy compared to chemical reactions. This is true because nuclear reactions involve forces much stronger than those in chemical reactions, thus releasing significantly more energy.

Analyze Statement (e)

Statement (e) notes that nuclear fission causes a chain reaction due to neutron production. This is correct, as fission of a nucleus like U-235 releases more neutrons, which can induce fission in other nuclei, leading to a self-sustaining chain reaction.

Determine False Statement

Based on the analysis, statement (a) is false because it incorrectly states that fission is initiated by beta particles instead of neutrons.

Key concepts

Neutron-induced fission

Nuclear fission is initiated when a heavy nucleus, like uranium-235 or plutonium-239, absorbs a slow-moving neutron. This absorption destabilizes the nucleus, causing it to split into two or more smaller nuclei (often called fission fragments), along with a few additional neutrons and a significant amount of energy. Neutrons are particularly effective at inducing fission because they do not possess an electric charge. This means they can easily penetrate the strong electrostatic forces of repulsion from the protons in heavy nuclei. Unlike beta particles, which are high-speed electrons or positrons, neutrons can be absorbed directly, making them much more efficient in initiating fission reactions. This process is not only central to the operation of nuclear reactors but also critical for the continuation of a chain reaction, as we will discuss later.

Energy release in fission

The energy release in nuclear fission is a manifestation of the conservation of mass-energy, as proposed by Einstein's famous equation, \(E=mc^2\). During fission, the total mass of the resulting fragments is slightly less than the mass of the original nucleus. This small "loss" of mass is converted into energy.
The energy released per fission event is in the order of several million electron volts (MeV) — orders of magnitude higher than energy released in typical chemical reactions, which are usually measured in electron volts (eV).

• This energy is released in the form of kinetic energy of the fission fragments.
• Some energy is carried away by the emitted neutrons and gamma rays.
• The rest is released as heat and can be utilized to produce electricity in nuclear power plants.

The high energy output in fission reactions is what makes them so potent, especially when used for producing electricity or in the context of nuclear weapons.

Chain reactions in nuclear fission

Chain reactions are a defining feature of nuclear fission that allow it to produce continuous power or explosive power, depending on its control. Upon splitting, each fission event of a nucleus like uranium-235 releases additional neutrons. These free neutrons can collide with other fissionable nuclei in the vicinity, causing further fission events. If each fission leads to at least one more, a self-sustaining chain reaction can occur.

• In controlled environments, such as nuclear reactors, chain reactions are carefully managed to maintain a steady output of energy. This is achieved by using control rods that absorb excess neutrons and prevent the reaction from becoming too rapid.
• In uncontrolled environments, as in nuclear weapons, the chain reaction rapidly accelerates, releasing a massive amount of energy in a very short time period.

Understanding the balance and control in nuclear chain reactions is essential for both peaceful and military applications of nuclear technology.