Production and Properties of Radiation

Question 1

Planck’s constant

Answer 1

h

6. 626×10^−34 J⋅Hz−1
7. 136×10^−15 eV⋅Hz−1

Question 2

Electromagnetic Spectrum

Answer 2

In order of increasing energy:

Radio waves - microwaves - infrared - rainbow colors, visible light - UV rays - extreme UV rays - x-rays, gamma rays and Cosmic rays.

Question 3

Particles

used in radiation therapy

Answer 3

Electrons, protons, alpha particles, carbon ions (and other ions), pions.

Question 4

Not a particle

for the purpose of radiation therapy

Answer 4

Photons

Question 5

Photon momentum

equation

Answer 5

p = hν/c = h/λ

ν : Frequency
λ : Wavelength
h : Planck constant
c : Speed of light

Question 6

Photon energy

equation

Answer 6

E = hν = hc/λ

ν : Frequency
λ : Wavelength
h : Planck constant
c : Speed of light

Question 7

Avogadro’s number:

Answer 7

N_A = 6.022 × 10^23

Question 8

Directly ionizing radiation

which particles, and how is energy deposited

Answer 8

Energy is deposits in the medium through direct Coulomb interactions between the directly ionizing charged particle and orbital electrons of atoms in the medium.

Question 9

Indirectly ionizing radiation

which particles, and how is energy deposited

Answer 9

Non charged particles (photons or neutrons) deposits energy in the medium through a two step process:

● In the first step a charged particle is released in the medium (photons release electrons or positrons, neutrons release protons or heavier ions);

● In the second step the released charged particles deposit energy to the medium through direct Coulomb interactions with orbital electrons of the atoms in the medium

Question 10

Minimum energy of ionizing radiation?

Maximum wavelength of electromagnetic ionizing radiation?

Answer 10

12.4 eV / 100 nm according Art. 2 Swiss RPO/StSV

Rydberg energy: E_R = 13.61 eV

Question 11

Speed of light

Answer 11

c = 299 792 458 m/s ≈ 3 × 10^8 m/s

Question 12

Specific charge of electron

Answer 12

e/me = 1.758 × 10^11 C/kg

Question 13

Electron charge

Answer 13

e = 1.602 × 10^–19 C

Question 14

Lower energy limit for X-rays

Answer 14

124 eV / 10 nm.

Arbitrary border between extreme UV and X-ray

Question 15

K shell binding energies for atoms with Z > 20

Answer 15

E_B(K) = E_R(Z-2)^2

E_R =

Question 16

Sources of photon radiation

Answer 16

γ-rays : resulting from nuclear transitions.

Characteristic x-rays: resulting from electron transitions between atomic shells / orbits.

Bremsstrahlung: resulting from electron–nucleus Coulomb interactions

Annihilation quanta: resulting from positron–electron annihilation. Two 0.511 MeV photons in opposite direction

Question 17

The components of an X-Ray tube.

Answer 17

• Evacuated chamber / Glass envelope
• Heated filament(s) (cathode)
• Focusing cup (negatively charged vs fillament)
• Rotating High-Z target (anode, tungsten)
• Rotor to turn anode
• External stator windings.
• Oil filled housing (oil for cooling and electrical insulation)
• Electrical connections for filament, anode, cathode, overheat sensor.
• Exit window.
• Filter for beam hardening (remove low energy photons which do not contribute to image quality but would add to patient dose and scattering)

Question 18

The production of Bremsstrahlung (in an x-ray tube or linac)

Answer 18

Electrons are produced: Cathode is heated, liberating electrons via thermionic emission.

Electrons are accelerated: high voltage electric field in a vacuum (x-ray tube, linear accelerator with multiple stages).

Electrons are Decelerated: electrons have their paths bent and slowed down by high Z material –> Bremstrahlung.

Z^2×z /m

z: charge of particle, m: mass of particle

Note: 99 % of the energy is converted to heat.