plate. They can burn skin severely but cannot reach internal organs. Alpha particles have
low penetrating ability and cannot damage or penetrate skin. They can damage sensitive
internal tissue if inhaled, however. The high-energy gamma rays have great penetrating
power and severely damage both skin and internal organs. They travel at the speed of
light and can be stopped by thick layers of concrete or lead.
26-4 Radioactive Decay 1009TABLE 26-3 Common Types of Radioactive EmissionsType and Symbola Identity Mass (amu) Charge Velocity Penetrationbeta ( , ^01 , ^01 e) electron 0.00055 1 90% speed of light low to moderate,
depending on energy
positronb(^01 , ^01 e) positively charged 0.00055 1 90% speed of light low to moderate,
electron depending on energy
alpha ( ,^42 ,^42 He) helium nucleus 4.0026 2 10% speed of light low
proton (^11 p,^11 H) proton, hydrogen 1.0073 1 10% speed of light low to moderate,
nucleus depending on energy
neutron (^10 n) neutron 1.0087 0 10% speed of light very high
gamma (^00 ) ray high-energy electro- 0 0 speed of light high
magnetic radiation
such as X-rays
aThe number at the upper left of the symbol is the number of nucleons, and the number at the lower left is the number of positive charges.
bOn the average, a positron exists for only about a nanosecond (1 10 (^9) second) before colliding with an electron and being converted into the corresponding amount
of energy.
A technician cleans lead glass blocks that form part of the
giant OPAL particle detector at CERN, the European center
for particle physics near Geneva, Switzerland.
Robotics technology is used to manipulate
highly radioactive samples safely.