Interaction between Radiation and Matter

Question 0

Describe elasticitet and inelastic collisions of beta-particles

Answer 0

Elastic: collision with a nucleus or tightly bound electron without energy transfer but change of direktion of the beta-particle

Inelastic: Involves energy transfer to electrons leading to ionisation (High energy) or excitation (low energy)

Question 1

Which kinds of interactions can a beta- particle undergo?

Answer 1

Elastic and inelastic collisions
Bremsstrahlung
Cherenkov radiation
Annihilation for beta(+) particles

Question 2

Describe Bremsstrahlung

Answer 2

For beta-particles with energy higher than 1MeV
These beta-particles can be deflected when passing close by a nucleus under conversion of part of the kinetic energy to a photon

Question 3

Describe Cherenkov radiation

Answer 3

Applies when the velocity of an energy-rich beta-particle is higher that the velocity of light in that medium (There is a energy threshold).
The beta-particle gives off part of its energy as a photo n with short wave lenght (250-600nm)

Question 4

Which kind of interaction can alpha-particles undergo?

Answer 4

Exclusively inelastic collisions

Leading to ionisation, excitation (and emission of x-rays)

Question 5

Which kinds of interactions can a neutrons undergo?

What is the interaction dependent on?

Answer 5

Elastic collision
Inelastic collision (neutron capture)
Alternativly, the neutron decays to a proton, a beta(-)particle and a antineutrino.
The interaction is dependent on the velocity(energy) of the neutron.

Question 6

Neutron radiation is classified by velocity of the neutron. Give the four classes, the energy and the most probable interaction mechanism.

Answer 6

Slow or thermic neutrons (E20MeV). Disintegration

Question 7

Describe elasticitet collision of neutrons and explain moderation.

Answer 7

A neutron transfer a part of its kinetic energy to a nucleus and loses velocity (modreation).
Nucleuses with masses close to the neutrons mass (H-atom) will cause the greatest energy transfer.
Moderation: decrease of velocity causer by elasticitet collisions freenig H(+)ions.

Question 8

Describe inelastic collision of neutrons

Answer 8

A slow neutron os captured into the nucleus which becomes highly excited thus emitting alpha-, proton-, neutron-, or gamma-radiation.

Question 9

What kinds of interaction can photon-radiation undergo?

What determines the interaction mechanism?

Answer 9

Raleigh scattering
Photoelectric absorption
Compton absorption and diffusion
Pair production and annihilation

Depends on atomic number of the material and energy of the photon.

Question 10

Describe Raleigh scattering. When does it occur?

Answer 10

The photon interacts with the atom as a whole. Hardly any energy transfer, but the photon charges direction.
Occurs with protons of low energy.

Question 11

Describe photoelectric absorption. When does it occur?

Answer 11

A photon transfers all its energy to an electron (K- or L-shell, impulse transfer to nucleus) which is removed from the atom (=ionisation).
The photo electron can ionise other atoms and x-rays will be emitted when the electron is replased
Occurs with substances with high atomic number and up to a limited energy value

Question 12

Describe Compton effect. When does it occur?

Answer 12

Only part of the total amount of photon energy is transferred to an electron. The electron is freed and the rest of the energy continues as a photon of lower energy in another direction (Compton electron and scattered photon).
The Compton electron can ionise other atoms (if the energy is high enough) the scattered photon will continue to efter Compton processes until the energy is reduced below the limit and a photoelectric effect occur.
Occurs over a limiting energy value of the photoelectric process.

Question 13

Describe pair production and annihilation. When does it occur?

Answer 13

When high energic photons come close to a nucleus the energy can be transformed to mass (an electron and a positron) because of the Electric field of the nucleus. Both the electron and position will recieve 0.511MeV and the remainder energy will be divided as kinetic energy between the two. They both cause ionisation allonge their routes. When the positron bekomnes thermic it Uniteds with a neighbouring electron (= annihilation). The mass is converted into two photons emitted in an angle of 180 degrees.
Occurs with photon energies lagrer than 1.002MeV