MEDRADSC 2X03 - Lecture 3 - Chemistry of Radiation Absorption in Cells

how are high energy neutrons produced?

they are produced in linear accelerators with energies of 10 MeV or higher, in which they are by-products of x-ray photons and electrons

what is different about matter interactions with high-energy neutrons compared to x-ray photons?

high-energy neutrons can undergo multiple scattering events

what are the two types of neutron interactions with matter?

elastic scattering and inelastic scattering

elastic scattering

a recoil proton is produced, and the total kinetic energy is conserved

inelastic scattering

some of the energy transferred is used to overcome binding forces, and results in spallation products, the total kinetic energy is not conserved

spallation products

nuclear fragments produced as a result of inelastic scattering

which level of energy is required for direct ionizing radiation effects?

high LET/high energy charged particles

examples of high LET radiation

alpha particles, protons and high energy electrons

what energy level is required for indirect ionizing radiation effects?

low LET/low energy uncharged particles

examples of low LET radiation

x-rays, gamma rays and neutrons

what are the two ways in which a cell is damaged by radiation?

direct action and indirect action

direct action damage

high LET radiation interacts and causes bond breakage within the critical target

indirect action damage

low LET radiation interacts with water in the cell and causes the formation of free radicals which interact with and cause bond breakage within the critical target

what type of interaction causes over 2/3's of radiation damage to cells?

indirect action

what are the three main types of free radicals formed from the ionization of water?

hydrogen radical, hydroxyl radical and hydroperoxyl radical

how is a hydrogen radical formed?

when water is ionized, the water molecule dissociates into a hydrogen radical and a hydroxyl ion

how is a hydroxyl radical formed?

when water is ionized, it results in a fast electron which can interact with another water molecule, which causes it to be unstable and dissociates into a hydrogen ion and a hydroxyl radical

how is a hydroperoxyl radical formed?

a resultant hydrogen radical can react with oxygen to form a hydroperoxyl radical

what is the cytotoxic compound formed when two hydroxyl radicals react together?

hydrogen peroxide

which of the three free radicals produced by the ionization of water accounts for 2/3's of damage to cells?

hydroxyl radical

what is the oxygen effect, and how can it be negatively impacting on cells in relation to free radicals?

the extremely short lifespan of free radicals is lengthened when oxygen is present by reducing the probability of free radicals recombining with water

what are the two outcomes of bond breakage due to radiation?

chemical bond repair or chemical bond breakage

what are the two cell responses to damage to the critical target?

enzymatic repair or no repair and chemical change resulting in biologic change

what are the two outcomes of irreparable damage to the DNA?

cell death or DNA mutation

what happens when there is mutation of DNA of germ cells?

hereditary effects

what happens when there is mutation of DNA of somatic cells?

induction of cancer