L 1: Physics and chemistry of Radiation Absorption Flashcards
Alpha/Beta ratios of various tissues
Planck’s constant
- Universal value that relates the energy of a photon and its frequency.
- E=hv
Carbon Ions
1) Have less lateral scattering ( so have sharper beams)
2) RBE is higher
3) OER is lower
4) Small tail post bragg peak.
5) Have an exit dose unlike protons.
UV Rays
- Type of electromagnetic radiation that induces formation of pyrimidine dimers in DNA but not ionizing form of radiation.
. - Thymine dimers -> Mutations -> Skin cancers
Xeroderma pigmentosa
- Have mutations in genes that repair UV rays caused DNA damage.
- Nucleotide Excision Repair gene mutation
- Due to this increase risk of skin cancers.
Neutrons
1) Have higher RBE
2) Have lower OER
3) Higher LET
4) Indirectly ionizing and lead to recoil protons, alpha particles and heavier nuclear fragments
Direct DNA Damage
- High LET forms predominantly cause DNA damage directly.
- Directly ionizing
Indirect DNA Damage
- 2/3 of Low LET is indirect and 1/3 is direct damage
- Indireclty ionizing are electromargnetic radiations; x-rays, gamma-rays
Ionization
- If the radiation has sufficient energy to eject one or more electrons from the atom or molecule the process is called ionization and that radiation is called ionizing radiation.
- Electromagnetic radiations are considered ionizing if they have a photon energy in excess of 124 eV, which corresponds to wavelength shorter than 10 to the power -6cm.
Energy release during ionzation event
33eV
Enough energy to break a strong chemical bond
Electromagnetic radiations
- x-rays and gamma-rays
- radio waves
- radar
- visible light
x-rays
- produced extranuclear.
- x-rays are produced in an electrical device.
- accelarates electrons to high energy and then stop abruptly by a target (tugsten/gold filament).
- Part of this kinetic energy is converted to x-rays
gamma-rays
- Produced intranuclear.
- They are emitted by radioactive isotopes.
- It is the excess energy that is given off as the unstable nucleas decays to reach a stable form.
Electrons
- Small, -ve charged particles.
- Can be accelarated to high energy by electrical device such a betatron/linac.
Protons
- +ve charged, very heavy (~2000 times more than electron).
- Cyclotrons are used to accelarate them to useful energy.
- Part of space radiation.
alpha particles
- Nuclei of He
- 2 protons + 2 neutrons
- Major source of background radiation
- High LET
Neutrons
- same mass as protons but no charge
- Since they do not have charge they cannot be accelarated to produce electrons.
- They are produced as a by product during heavy radioactive atoms undergoing nuclear fission.
- Part of space radiation
Heavy charged particles
- nuclei of elements such as carcbon ion, argon, neon, iron.
- needs to be accelarated to very very high energy to produce electrons.
- Major part of space radiation.
Radioprotective compounds
- Scavenge the free radicals
- Effective for x-rays and gamma-rays
- Little use for neutrons, alpha particles or heavier ions.
Low LET
X-rays
Gamma-rays
Protons
High LET
- Alpha particles, Carbon ion
- They are all directly ionizing.
- They have 0 to very less sublethal damage and most are DS DNA breaks
Pair Production
Board question
Least stable ionized compound
Ionized water molecule
free radical?
Has an unpaired electron in the outter most shell
Neutrons
MOST of them are hit by direct action
not all but most!
Glutathione peroxidase
Radio protectant.
Uses sulphadryl molecules attaches to the free radical and changes to reductase,
Radiation quantity
SI Units
Absorbed dose
Dose equivalent
Memorize these!!
