Maximum damage of DNA is caused by:
a. Alpha particle an electrically charged ( + ) particle emitted from the nucleus of some radioactive chemicals, cf. plutonium. It contains 2 protons and 2 neutrons, and is the largest of the atomic particles emitted by radioactive chemicals. It can cause ionisation.
b. Beta particle an electrically charged ( - ) particle emitted from some radioactive chemicals. It has the mass of an electron. Krypton 85, emitted from nuclear power plants, is a strong beta emitter. Beta Particles can cause ionisation.
c. Gamma ray short wave-length electromagnetic radiation released by some nuclear transformations. It is similar to X-ray and will penetrate through the human body. Iodine 131 emits gamma rays. Both gamma and X-rays cause ionisation
d. Radiations differ not only by their constituents (electrons, protons, neutrons, etc.) but also by their energy.
e. Radiations that cause dense ionization along their track (such as neutrons) are called high-linear-energy-transfer (high-LET) radiation, a physical parameter to describe average energy released per unit length of the track.
f. Low-LET radiations produce ionizations only sparsely along their track and, hence, almost homogeneously within a cell.
g. Radiation dose is the amount of energy per unit of biological material (e.g., number of ionizations per cell).
h. High-LET radiations are more destructive to biological material than low-LET radiations--such as X and gamma rays--because at the same dose, the low-LET radiations induce the same number of radicals more sparsely within a cell, whereas the high-LET radiations--such as neutrons and alpha particles--transfer most of their energy to a small region of the cell.