# I recently saw in my physics textbook a diagram of a positron and a

• Sofie1990
In summary, the conversation discusses the creation and movement of a positron and electron in pair production. The diagram described shows the particles moving in opposite directions before spiraling inwards, which suggests the influence of a magnetic field. However, the decrease in radius of curvature suggests that the particles are also losing energy and momentum due to interactions with the substance they are traveling through. This is further explained by the Bethe-Bloch equation, which accounts for the particles' spiral inward until they stop.
Sofie1990
i recently saw in my physics textbook a diagram of a positron and a electron being created in pair production. The diagram showed that as soon they where created, they moved in opposite directions and then they spiralled inwards a bit. Now i think the reason why they move in opposite directions is because of the magnetic field, however, if that is the case they why do they then spiral inwards? surely if it is the magnetic field, then shouldn't the electron and positron keep going in opposite directions and not be curling inwards?.
Any help would be appreciated.

Sofie1990 said:
why do they then spiral inwards?

The picture you saw was probably made using a bubble chamber. The particles are traveling through some substance (e.g. liquid hydrogen), and lose energy through interacting with the atoms of that substance. As they lose energy, they also lose momentum, and the radius of curvature decreases (assuming the strength of the magnetic field stays constant).

(Same as ltbell) See http://www.alternativephysics.org/book/MatterEnergy2.htm

When a positron and electron are created (by a photon) in the Coulomb field of a nucleus, they generally move away from the creation point with an opening angle between them. The angle is usually less than 90 degrees; never 180 degrees. If they were created in a magnetic field (like a bubble chamber), they would spiral in opposite directions. As they lose energy from ionization (Bethe-Bloch dE/dx) in the bubble chamber, they would spiral inward until they stop.

## 1. What is a positron and how does it differ from an electron?

A positron is a subatomic particle with the same mass as an electron but with a positive charge. This is in contrast to an electron, which has a negative charge. Positrons are the antiparticles of electrons and have the same spin and magnetic moment, but opposite charge.

## 2. How was the existence of positrons discovered?

Positrons were first theorized by physicist Paul Dirac in 1928. They were later discovered in 1932 by Carl Anderson in cloud chamber experiments, where they were observed as a new type of particle that curved in the opposite direction to electrons in a magnetic field.

## 3. What role do positrons play in particle physics?

Positrons are important in particle physics as they are one of the fundamental particles that make up the Standard Model of particle physics. They also play a role in antimatter research and have practical applications in medical imaging technology.

## 4. How are positrons produced in laboratory settings?

Positrons can be produced through various methods in laboratory settings, including the decay of radioactive elements, high-energy collisions of particles, and through the use of particle accelerators. They can also be generated through the annihilation of gamma rays with matter.

## 5. What potential impact could the study of positrons have on our understanding of the universe?

The study of positrons has the potential to greatly expand our understanding of the universe, as they provide valuable information about the behavior of antimatter and can shed light on the fundamental forces that govern our universe. They also play a role in the study of dark matter and the search for new physics beyond the Standard Model.

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