Before revision: When purchased new a typical 252Cf neutron source emits 107 to 109 neutrons per second ; but with a half-life of 2.6 years, neutron output drops by half in 2.6 years.
After revision: Awhen new typical 252Cf neutron source emits 107 to 109 neutrons per second ; but with a half-life of 2.6 years, neutron output drops by half in 2.6 years.