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A neutron in a reactor makes an elastic head-on collision with a carbon atom that is initially at rest. (The mass of the carbon nucleus is about 12 times that of the neutron.) (a) What fraction of the neutron’s kinetic energy is transferred to the carbon nucleus? (b) If the neutron’s initial kinetic energy is 1.6 3 10213 J, find its final kinetic energy and the kinetic energy of the carbon nucleus after the collision.

Short Answer

Expert verified
About 64% of the neutron's kinetic energy is transferred to the carbon nucleus during the collision. The final kinetic energy of the neutron is \(0.576 \times 10^{-13}\) J, while the kinetic energy of the carbon nucleus after the collision is \(1.024 \times 10^{-13}\) J.

Step by step solution

01

Understand the Principles Guiding the Collision

In an elastic collision, two important quantities are conserved: total kinetic energy and total momentum. The aim is to work with these principles to solve the problem. The given mass of the carbon atom is 12, and that of the neutron can be taken as 1. Applying the law of conservation of energy and the law of conservation of momentum gives two foundational equations. First, \(v_1 = \frac{(m_1 - m_2)}{(m_1 + m_2)} u_1\), where u and v are the initial and final velocities respectively, and m stands for the mass. The subscripts 1 and 2 refer to the neutron and the carbon atom respectively. Since the carbon atom starts at rest, u2 = 0, and this simplifies to \(v_1 = \frac{(1 - 12)}{(1 + 12)} u_1\), which gives \(v_1 = - 0.846 u_1\). This negative sign signifies that the neutron has been deflected backwards.
02

Find the Fraction of Kinetic Energy Transferred

The initial kinetic energy of the neutron is \(KE_{initial} = \frac{1}{2} m_1 u_1^2\), while its final kinetic energy is \(KE_{final} = \frac{1}{2} m_1 v_1^2\). Expressing \(v_1\) in terms of \(u_1\) from the previous step, the final kinetic energy becomes \(KE_{final} = \frac{1}{2} m_1 (- 0.846 u_1)^2 \approx 0.36 KE_{initial}\). The energy transferred is thus simply \(KE_{initial} - KE_{final} \approx 0.64 KE_{initial}\). This means that approximately 64% of the kinetic energy of the neutron is transferred to the carbon atom.
03

Calculate the Final Kinetic Energies

The initial kinetic energy of the neutron is given as \(1.6 \times 10^{-13}\) J. From the results of the last step, the final kinetic energy of the neutron is \(0.36 KE_{initial} = 0.36 \times 1.6 \times 10^{-13} \approx 0.576 \times 10^{-13}\) J. On the other hand, the carbon atom receives approximately 64% of the kinetic energy of the neutron, which implies that its kinetic energy after the collision is \(0.64 KE_{initial} = 0.64 \times 1.6 \times 10^{-13} = 1.024 \times 10^{-13}\) J.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Kinetic Energy Transfer
In a collision, particularly an elastic one, kinetic energy transfer is a key concept. When objects collide, they exchange energy and momentum, depending on their masses and velocities. The fundamental characteristic of an elastic collision is that the total kinetic energy is the same before and after the collision.

In the case of a neutron colliding with a carbon atom, a significant part of the neutron's kinetic energy is transferred to the carbon atom. The transfer is determined by the relative masses of the neutron and the carbon atom. Since the carbon atom is about 12 times heavier than the neutron, a substantial portion of kinetic energy is transferred.

In this exercise, around 64% of the neutron's kinetic energy is transferred to the carbon atom, which tells us how much of its original energy the neutron lost. Understanding how kinetic energy is split helps explain how particles interact in atomic and subatomic processes.
Conservation of Momentum
Momentum, just like energy, is a conserved quantity in the universe. In any physical process, especially in collisions, the total momentum before and after the event remains constant. This principle simplifies the analysis and solutions of collision problems because we can set up equations based on momentum conservation.

The momentum of an object is the product of its mass and velocity. Thus, when a neutron collides with a carbon atom at rest, the combined momentum before and after the collision should be the same.

  • Before collision: The neutron has momentum as the product of its mass and velocity, while the carbon atom has zero momentum as it is at rest.
  • After collision: Both the neutron and the carbon atom have their velocities affected, but their total momentum remains unchanged.
This law assists in deriving equations that describe how velocities and subsequently, energy are shared between the neutron and carbon atom post-collision.
Conservation of Energy
The principle of conservation of energy states that in any isolated system, the total energy before and after a process remains unchanged. In the context of an elastic collision, this means that the kinetic energy of the colliding bodies is preserved overall, even though it gets redistributed between them.

When applying this principle to a neutron-carbon collision, the goal is to calculate how much kinetic energy each participant has after the collision occurs. The initial kinetic energy possessed by the neutron is partly retained by it and partly transferred to the carbon atom.

  • Initial Total Energy: Only the neutron has kinetic energy as it moves towards the stationary carbon atom.
  • Final Total Energy: Both the neutron and carbon atom have kinetic energy, but their combined total is unchanged from the initial total.
Understanding the conservation of energy allows us to compute the final kinetic energies of both particles, ensuring that no energy is lost in the process.
Neutron-Carbon Collision
In the world of atomic physics, a neutron-carbon collision is an important interaction to study. Such interactions are fundamental in nuclear reactors and in the understanding of atomic behavior. Neutrons are uncharged particles, making them excellent candidates for experiments involving nuclear reactions, as they do not easily interact with electrons or other charged particles.

During an elastic head-on collision with a carbon atom, the neutron impacts the structure of the carbon nucleus, causing energy transfer and momentum changes. The results of these collisions help scientists understand nuclear forces and behaviors of atoms under various conditions.

The neutron's lack of charge allows it to penetrate materials and initiate nuclear reactions without being repelled, unlike charged particles. Studying how energy and momentum are conserved during these specific collisions improves our insight into atomic-scale physics and the design and operation of nuclear reactors.

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Most popular questions from this chapter

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