delayed neutron
Technical term in nuclear physics: a neutron emitted by a fission product some time after the fission event, crucial for reactor control.
Delayed neutrons play an important role in nuclear reactor control.
即発中性子 (prompt neutron) is emitted immediately during fission, while 遅発中性子 is emitted later by fission products.
Compound of 遅発 (delayed emission) + 中性子 (neutron). The exact historical derivation is uncertain; the term is a modern technical coinage.