Figure 4 Alpha particle (or nucleus of a helium atom)

Tritium Primer

DOE-HDBK-1079-94

RADIOLOGICAL FUNDAMENTALS

2 neutrons, 2 protons

no electrons

Figure 4 Alpha particle (or nucleus of a helium atom)

to ionize nearby atoms as it passes through body tissue. The strong positive charge and its

relatively slow speed (resulting from its large mass) causes the alpha particle to interact strongly

with orbiting electrons of atoms and molecules and to lose large amounts of energy in a short

distance. This limits the penetrating ability of the alpha particle, making it easy to stop. A few

centimeters of air, a sheet of paper, or the outer layer of skin stops alpha particles (Figure 5).

Paper or outer layer of skin

Figure 5 Alpha shielding

Alpha particles are not an external radiation hazard because they are easily stopped by protective

clothing or the outer layer of skin. However, if an alpha emitter is inhaled or ingested, it becomes

an internal radiation hazard. Because the source is in close contact with body tissue, the alpha

particle will dissipate its energy in a short distance of the tissue.

beta particle ( )--is equivalent to an electron except for its source. Beta-emitting

nuclides have too many neutrons. A neutron emits a particle, and the neutron is then

converted to a proton. Tritium decay provides a good example of this process:

+ 3He + energy .

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Tritium