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A gamma ray (a high-energy photon) can produce an electron \(\left(\mathrm{e}^{-}\right)\) and a positron \(\left(\mathrm{e}^{+}\right)\) when it enters the electric field of a heavy nucleus: \(\gamma \rightarrow \mathrm{e}^{+}+\mathrm{e}^{-} .\) What minimum gamma-ray energy is required to accomplish this task? (Note: The masses of the electron and the positron are equal.)

Short Answer

Expert verified
The minimum gamma-ray energy required to create an electron and a positron is approximately \(1.64 \times 10^{-13}\) Joules.

Step by step solution

01

Understand the Mass of Particles

Before proceeding, it is important to understand that both electron and positron have the same mass. This mass (\(m\)) is approximately \(9.11 \times 10^{-31}\) kilograms.
02

Understand Einstein's Mass-Energy Equivalence

The principle that will be used to solve this problem is Einstein's mass-energy equivalence. This principle is mathematically represented by the formula \(E=mc^2\). It states that the energy (\(E\)) of an object is equal to the mass (\(m\)) of that object times the speed of light (\(c\) approximately \(3 \times 10^8\) m/s) squared.
03

Calculate Energy of Individual Particles

Using the Einstein's mass-energy equivalence formula, the energy (\(E\)) of a single electron or positron can be calculated by: \(E = m \times c^2\). Substituting the known values gives: \(E = 9.11 \times 10^{-31} \times (3 \times 10^8)^2\) joules.
04

Calculate Total Energy Required

The total energy required to create both an electron and a positron will be twice the energy calculated in the previous step. Hence, the minimum gamma ray energy required is: \(2 \times E = 2 \times (9.11 \times 10^{-31} \times (3 \times 10^8)^2)\) joules.

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Key Concepts

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

Electron-Positron Pair Production
Electron-positron pair production is a fascinating phenomenon that epitomizes the interplay between energy and matter. In this process, a single gamma ray, which is essentially a packet of pure energy, can transform into two particles – an electron (\( \text{e}^- \) ) and a positron (\( \text{e}^+ \) ), the latter being the antimatter counterpart of the electron. This conversion occurs in the vicinity of a heavy nucleus, which provides the necessary electric field for the gamma ray to materialize into matter.

According to the principles of quantum physics, the amount of energy required must be equivalent to the combined mass-energy of the electron and the positron. It's an example of matter and antimatter being born from energy, which perfectly illustrates one of the most intriguing aspects of fundamental particles physics. However, it is crucial that the incoming gamma ray possesses a minimum amount of energy to make this possible, otherwise, the production cannot occur.
Einstein's Mass-Energy Equivalence
Einstein’s mass-energy equivalence is a principle that has changed the way we understand the universe. Encapsulated in the iconic equation \( E=mc^2 \) , the principle asserts that mass (\( m \) ) can be transformed into energy (\( E \) ) and vice versa. Here, \( c \) represents the speed of light in a vacuum (\( 3 \times 10^8 \) m/s). It implies that a tiny amount of mass can be converted into a colossal amount of energy.

When it comes to pair production, this equivalence provides the calculation for the minimum energy a gamma ray must have to create an electron and a positron. The energy equivalence of the particles' rest mass is the threshold energy for the gamma ray. Through this remarkable concept, we grasp how the energy of a gamma ray gets converted into the mass of fundamental particles.
Speed of Light
The speed of light, denoted by \( c \) , is not merely a high velocity; it is a cornerstone of modern physics, acting as a cosmic speed limit for anything with mass. In a vacuum, it is precisely calculated to be approximately \( 3 \times 10^8 \) meters per second. This constant is not just pivotal in the calculation of energy in Einstein's mass-energy equivalence equation but is also central to the laws of relativity which govern the behavior of objects at high speeds.

Within the context of pair production, the speed of light squared (\( c^2 \) ) amplifies the mass of an electron and positron to obtain the energy required for their creation. The massive value of \( c^2 \) highlights the incredible energy contained within a small amount of mass, enabling processes like pair production to take place in high-energy astrophysical events.
Fundamental Particles Physics
Fundamental particles physics, a branch of physics focused on the smallest known building blocks of the universe, seeks to understand the behavior and interactions of particles that compose all matter. Electrons and positrons are among such particles - often depicted at the forefront of countless physics textbook illustrations and quantum theories.

The study of their properties and interactions, including processes like pair production, falls within the realm of quantum electrodynamics (QED), a theory that describes how light and matter interact. Phenomena like electron-positron pair production are significant because they exemplify how energy can give birth to matter, which is a mind-bending concept hailing from the depths of high-energy physics and helps in pushing the boundaries of our understanding of the material universe.

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Most popular questions from this chapter

An astronomer on Earth observes a meteoroid in the southern sky approaching the Earth at a speed of \(0.800 c\) At the time of its discovery the meteoroid is 20.0 ly from the Earth. Calculate (a) the time interval required for the meteoroid to reach the Earth as measured by the Earthbound astronomer, (b) this time interval as measured by a tourist on the meteoroid, and (c) the distance to the Earth as measured by the tourist.

The Principle of Galilean Relativity A \(2000-\mathrm{kg}\) car moving at \(20.0 \mathrm{m} / \mathrm{s}\) collides and locks together with a \(1500-\mathrm{kg}\) car at rest at a stop sign. Show that momentum is conserved in a reference frame moving at \(10.0 \mathrm{m} / \mathrm{s}\) in the direction of the moving car.

Two jets of material from the center of a radio galaxy are ejected in opposite directions. Both jets move at \(0.750 c\) relative to the galaxy. Determine the speed of one jet relative to the other.

In a laboratory frame of reference, an observer notes that Newton's second law is valid. Show that it is also valid for an observer moving at a constant speed, small compared with the speed of light, relative to the laboratory frame.

A rod of length \(L_{0}\) moving with a speed \(v\) along the horizontal direction makes an angle \(\theta_{0}\) with respect to the \(x^{\prime}\) axis. (a) Show that the length of the rod as measured by a stationary observer is \(L=L_{0}\left[1-\left(v^{2} / c^{2}\right) \cos ^{2} \theta_{0}\right]^{1 / 2}\) (b) Show that the angle that the rod makes with the \(x\) axis is given by \(\tan \theta=\gamma \tan \theta_{0} .\) These results show that the rod is both contracted and rotated. (Take the lower end of the rod to be at the origin of the primed coordinate system.)

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