Final answer:
The key reason isotopes emitting alpha radiation are less dangerous outside the body is that alpha particles cannot penetrate skin, making them relatively harmless unless ingested or inhaled. Gamma radiation, however, poses a risk both inside and outside the body due to its high penetration power, which can deeply penetrate tissues and cause damage.
Step-by-step explanation:
Isotopes that emit α (alpha) radiation are relatively safe outside the body because alpha particles are easily blocked by materials like skin. On the other hand, γ (gamma) rays are hazardous both outside and inside the body due to their high penetrating ability, which allows them to pass through tissues and other materials. Gamma rays can be hazardous outside the body because they penetrate the body's external barriers, such as the skin, and can damage internal tissues and organs.
The reason that alpha-emitting isotopes are dangerous inside the body is that if they are ingested or inhaled, the internal tissues absorb all of their energy, leading to high levels of localized damage. Gamma rays are also hazardous inside the body since they can penetrate deeply and cause significant ionization and tissue damage.
Therefore, the correct answer to why isotopes that emit alpha radiation are relatively safe outside the body and exceptionally hazardous inside, while gamma emitters are hazardous both outside and inside, is: a) Alpha particles are easily blocked by skin; gamma rays penetrate tissues.