Britannica Sources used in this answer

How can a Geiger counter containing boron trifluoride detect neutrons?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A labeled diagram of the periodic table entry for boron shows its atomic number 5, symbol B, electron configuration, atomic weight range, and classification as a solid, weakly acidic, other nonmetal with a rhombohedral crystal structure at room temperature. — boron Properties of boron.

A Geiger counter typically cannot detect neutrons directly because neutrons lack an electric charge. To enable detection, the counter's gas chamber is filled with boron trifluoride (BF $_{3}$ ) gas, which acts as a converter.12

When a neutron enters the chamber, it may be captured by a boron-10 nucleus. This nuclear reaction results in the emission of an alpha particle. Because alpha particles are charged, they ionize the gas within the chamber, leaving a trail of ion pairs that trigger a response in the counter. By recording these alpha particles, the device effectively registers the presence of the neutrons that initiated the reaction.12