1.4 Particles and Anr

What is annihilation?

Annihilation is the process where a particle and its antiparticle collide and transform their mass into energy.

How does a PET scanner work?

1. A positron-emitting isotope is administered to the patient, reaching the brain via the blood system.

2. Each emitted positron travels a few millimetres before annihilating with an electron, producing two gamma photons.

3. These photons are sensed by detectors linked to computers, gradually building an image of the positron-emitting nuclei inside the brain

Antiparticle of a electron

positron

When is a positron emitted?

a proton changes into a neutron

What is emitted as a co product of positron emission?

neutrino

How are positron emitting isotopes manufactured?

a beam of protons is directed on a solid/liquid stable isotope

the nuclei absorb extra protons

Uses of PET scanners

brain imaging

What kind of radiation is detected in a PET scanner?

gamma

Who first predicted antimatter?

Dirac

Einstein said that the mass of a particle when it is stationary, its ____ _____ , corresponds to r____ ________ locked up as _____.

rest mass

rest energy

mass

Einstein’s equation for energy

E=mc²

Dirac's theory of antiparticles predicted that for every type of particle there is a corresponding antiparticle that:

1. annihilates the particle and itself if they meet, converting their total mass into photons

2. has exactly the same rest mass as the particle

3. has exactly opposite charge to the particle if the particle has a charge

When does pair production occur?

when a photon with sufficient energy passing near a nucleus or electron suddenly changes into a particle-antiparticle pair

1 MeV in J

1.63 × 10 ^-13

What is one electron volt?

energy transferred when one electron is moved through a pd of 1 V

What is the minimum energy of each photon produced during annihilation?

half the energy of both particle and antiparticle

How much energy does a photon need for pair production?

same energy as the particle-antiparticle pair

Pair production

a photon creates a particle and a corresponding antiparticle, and vanishes in the process

What is a cloud chamber used for?

To see the path of alpha and beta particles.

What does a cloud chamber contain?

Air saturated with vapor and made very cold.

What happens when ionizing particles pass through the air in a cloud chamber?

They leave a visible trail of liquid droplets.

Who discovered the first antiparticle using a cloud chamber?

Carl Anderson.

A positive particle would be deflected by the magnetic field in the opposite direction to a __ particle traveling in the same direction.

negative

What would happen to the trail of a slower particle in a magnetic field?

It would bend more.

In 1932, Carl Anderson was photographing trails produced by __ rays in a cloud chamber.

cosmic