Internal organs are generally protected from external β radiation, but exposed organs such as eyes are sensitive to damage. The slower rate of energy loss enables β particles to travel several meters through air and several centimeters through human tissue. Given their lower mass of approximately 5.5×10 −4 amu (9.130×l0 −24 g), interactions between β particles and the atoms of pass-through materials are much less frequent than α particle interactions: fewer than 200 ion pairs are typically formed in each centimeter of passage through air. Collisions between α particles and the atoms and molecules of human tissue may cause disorder of the chemical or biological structure of the tissue.īeta radiation is a stream of electrons emitted at a velocity approaching the speed of light, with kinetic energy between 0.2 MeV and 3.2 MeV. A health hazard occurs when material contaminated with α-emitting radionuclides is eaten or inhaled, or otherwise absorbed inside the body, so that organs and tissues more sensitive than skin are exposed to α radiation. 1 External radiation by α particles presents no direct health hazard because even the most energetic are stopped by the epidermal layer of skin and rarely reach more sensitive layers. α particles thus have a mass of about 4 amu (6.642×10 −4 g) each and a positive charge of 2. Controlled measurement of alpha (α), beta (β), and gamma (γ) radiationĪlpha radiation has been identified as helium nuclei that have been stripped of their planetary electrons, and each consists of two protons and two neutrons.
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