α-, β-, and γ-radiation are types of ionizing radiation. That means that when an α- or β-particle or γ-radiation strikes a molecule, electrons can be knocked out of their chemical bonds. The harmful effects of α-radiation are approximately 20 times greater than for β- or γ-radiation.
Expulsion of the electron leads to bond breakage within the molecule, and the formation of chemically reactive intermediates: radicals. The chance of two such radical fragments finding each other again and recombining to form an unreactive compound is relatively slight. Instead, the radicals react with other biological molecules and prevent them from functioning properly.
One particular event brought about by ionizing radiation is DNA strand cleavage, which also disrupts the organism’s genetic coding. When relatively little of this damage takes place, most of it can be remedied by DNA repair enzymes. However, irreversible damage can take place, such as in the case of leukemia when entire sections of DNA are clipped off from one chromosome and transferred to another. Increasing levels of nuclear radiation can both overwhelm the capabilities of the repair enzymes and increase the likelihood that an irreparable alteration will occur in the DNA.
Even if γ-radiation can be only poorly shielded, it should be pointed out that the uptake of radioactive isotopes into food is always a serious problem, no matter what type of radiation they emit. The uptake of radioactive isotopes followed by their incorporation into the body’s tissues means that the body will be subjected to radiation for a period of days or years.