Ionizing radiation

Ionizing radiation are…

are capable to penetrate deep in the matter, they can produce ionization of the atoms and can break chemical bonds thus living organisms. They occur when an electron is ejected from the atom shell

Effectiveness of IR (2)

• Mass, energy, charge of incident ionizing particle

• Atomic characteristics of particle

Types of ionizing radiation

Direct IR & indirect IR

Direct IR

includes charged particles (α, β, e⁺, p), which ionize atoms by direct collision.

Indirect IR

photons with high energy; gamma-rays, roentgen rays, and neutrons. Interact with atoms by their electromagnetic field.

Characteristic of direct IR:

• Linear ionization (N_L): number of ion pairs produced by the ionizing energy during their passage through the unit path in matter

• Linear energy transmission (LET): locally transmitted energy by particles per unit path.

• Range (R): average depth in a certain substance at which intensity of radiation decrease to half.

Photon radiations interact with the matter by several processes -

Elastic scattering, Photoelectric absorption, compton effect, pair production

Photoelectric absorption

• Emission of electron when light exceeding the threshold frequency is shone onto a material. The photon of light interacts with any electron and causes emission. Pair of ions is produced. Energy of photon is given by E= h.f = ct + E_k 

  • ct = the work done required to tear the electron from the orbit

  • E_k = is the remaining energy as kinetic energy.

Compton effect (scattering)

Occurs when photon interacts with free electron/ weakly bonded electron from outer shells. Photon transfers part of the energy to electron and continues propagation with altered direction and energy.

Roentgen radiation (X-rays)

photons with high energy

X-Rays properties:

• Roentgen range includes wavelength from 3 pm – 10 nm.

• For medical applications X-Rays with 100 pm – x (few) pm

X-Ray Sources:

• Natural sources: cosmic rays, during radioactive decay of some elements like thulium (K-catch process)

• Industrial source: X-ray tube

X-ray tube

 a scheme of a cathode tube: thermo-cathode is heated up by separated electric energy to be ejected from metal lattice. Electron beam hits the anode an produce emission of X-Ray.

Types of X-rays - Characteristic roentgen radiation (CR):

result of atomic conversions after strike of accelerated electron beam with electrons within anode’s metal.

Types of X-rays - Braking roentgen radiation:

emission of photons from decelerating electrons entering anode.

Probability of photoelectric effect appearance is formulated in  following equation:

τ ~ ρ.Z⁴ / (hv)³

ρ - density

z - atomic number

hv - energy of incoming photon