For thermal (slow-neutron) fission reactors, the typical prompt neutron lifetime is on the order of 10 seconds, and for fast fission reactors, the prompt neutron lifetime is on the order of 10 seconds. These extremely short lifetimes mean that in 1 second, 10,000 to 10,000,000 neutron lifetimes can pass. The average (also referred to as the adjoint unweighted) prompt neutron lifetime takes into account all prompt neutrons regardless of their importance in the reactor core ; the effective prompt neutron lifetime (referred to as the adjoint weighted over space, energy, and angle) refers to a neutron with average importance.