Alpha radiation is harmless outside the body because alpha particles cannot penetrate the outer dead layer of human skin, but it becomes deadly if inhaled because inside the body, alpha particles can directly damage living cells and tissues.
Alpha particles are made up of two protons and two neutrons, making them relatively large and heavy compared to other types of radiation particles. This size and mass cause alpha particles to have very low penetration power. When alpha radiation encounters the outer layer of skin, which consists of dead cells, it cannot pass through. This means that external exposure to alpha radiation generally does not harm the body because the particles cannot reach the living cells beneath the skin surface.
However, the situation changes drastically if alpha-emitting substances are inhaled, ingested, or enter the body through wounds. Inside the body, alpha particles are emitted very close to or directly within living tissues. Because alpha particles carry a lot of energy but travel only a very short distance—typically just a few cell diameters—they deposit all their energy in a very small area. This intense, localized energy release can cause severe damage to the DNA and cellular structures of the surrounding living cells.
This cellular damage can lead to mutations, cell death, or uncontrolled cell growth, which increases the risk of cancer and other serious health effects. For example, inhaling alpha-emitting radioactive particles like radon gas or its decay products can cause lung tissue damage and significantly raise the risk of lung cancer. The alpha particles’ inability to travel far means their destructive power is concentrated where the radioactive material lodges inside the body, making internal exposure far more dangerous than external exposure.
In summary, alpha radiation’s harmlessness outside the body is due to its inability to penetrate the skin’s dead outer layer, while its deadly nature inside the body arises from its high energy deposition over a very short range within living tissues, causing significant cellular and genetic damage.
