Figure 3 Neutral and ionized atoms

RADIOLOGICAL FUNDAMENTALS

DOE-HDBK-1079-94

Tritium Primer

Electrically charged atoms or molecules are called ions. Ions are either positively or negatively

charged, depending on the number of orbiting electrons relative to the number of protons in the

nucleus. As shown in Figure 3, ions with more electrons than protons are negatively charged,

while ions with more protons than electrons are positively charged. The process of breaking a

neutral atom or molecule into electrically charged parts is called ionization. This process

requires energy. Ionization removes electrons from the atom, or molecule, leaving an ion with

a positive charge. The negatively charged electron (which can attach itself to a neutral atom or

molecule) and the positively charged ion, are called an ion pair. Radiation that causes

ionization is called ionizing radiation.

Net

negative

Deficient

positive

Neutral

Excess

charge

electrons

charge

atom

electrons

Captured

electron

Free

electron

Figure 3 Neutral and ionized atoms

Types of Radiation

There are four basic types of ionizing radiation emitted from nuclei: alpha particles, beta

particles, gamma rays, and neutrons.

alpha particle ( )--consists of two protons and two neutrons and is the same as the

nucleus of a helium atom (4He) (Figure 4). Generally, only the heavy nuclides can emit

alpha particles.

A typical example of an -emitting nuclide is uranium-238:

238

+ 234 Th + energy .

The mass of an alpha particle is about four times the mass of a single neutron or proton, and

has a positive charge of +2 (it has no electrons). This positive charge causes the alpha particle

Tritium

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