How much radiation are you exposed to on a plane?

“If you use a classical dosimeter, it is measuring photons and electrons, but those account for less than 40% of the total dose aboard aircraft,” he says. “The difference comes from the fact that you have other particles like neutrons, and those represent most of what you receive in a dose aboard an airplane. They can’t be detected with classical dosimeter. You need very specific technology for that.”

Expensive, specialized dosimeters pick up the particles that are most common at flight altitudes. Normal, old dosimeters don’t. To McManis, that difference makes a lot of sense.

“I was using a personal alarm dosimeter that relies on ionizations to work, and neutrons don’t ionize things,” she says.

That last statement is a tad misleading. Neutrons are considered ionizing radiation. They just don’t register in dosimeters that rely on direct ionization through electrostatic interaction — neutrons are uncharged. Which means they penetrate and give a whole-body dose.

Neutrons can immediately ionize some things, like hydrogen — if you slam a high energy neutron into a proton (or other light nucleus), it will leave the electron behind, and both will be energetic and do damage to nearby molecules in the cell. Thermal neutrons typically do damage through absorption into a nucleus and causing it to become radioactive (neutron activation). The subsequent decay gives off ionizing radiation.