How can boron trifluoride help a Geiger counter detect neutrons?

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

A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — boron group element Modern version of the periodic table of the elements (printable).

Boron trifluoride ( $B F_{3}$ ) is used in proportional counters to detect slow neutrons by serving as both the target material and the counting gas.1

When an incident neutron interacts with the boron-10 isotope present in the $B F_{3}$ gas, it triggers a nuclear reaction:
$^{10} B + n \to^{7} Li + α$

This reaction releases charged particles (a lithium nucleus and an alpha particle) with a combined kinetic energy of 2.3 MeV. As these highly ionizing particles travel through the gas, they create a trail of ion pairs. This ionization produces an electrical pulse within the tube, which is then recorded by the detector. Because $B F_{3}$ functions effectively as a proportional gas only at pressures below one atmosphere, the detection efficiency is limited by the density of the boron nuclei within the tube.1