An ionization smoke detector contains a material which ionizes the air in the sensing chamber, thus rendering it conductive and permitting a current to flow between two charged electrodes. This gives the sensing chamber an effective electrical conductance. When smoke particles enter the ionization area, they decrease the conductance of the air by attaching themselves to the ions, causing a reduction in mobility. When the conductance is less than a predetermined level, the detector responds. What material ionizes the air in the sensing chamber?
A. a small amount of magnesium
B. a small amount of radioactive material
C. a small amount of copper material
D. a small amount of hydrogen gas
Answer: B. a small amount of radioactive material
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