Apparatus for determining number of neutrons emitted by fissile material during induced fissile

An apparatus for determining the number of neutrons respectively emitted as the result of induced fissions in a fissile material during first and second predetermined time intervals, comprising:

• first and second blocks of hydrogenated material arranged with said fissile material therebetween;
• a neutron source displaceably arranged in said first block of hydrogenated material;
• means for displacing said neutron source between first and second positions, said first position being sufficiently close to said fissile material that fissions are induced therein by neutrons emitted by said source, and said second position being sufficiently distant from said fissile material that a negligible number of fissions are induced therein by neutrons emitted by said source;
• first neutron detecting means arranged inside said first block of hydrogenated material in proximity to said first position;
• second neutron detecting means arranged inside said second block of hydrogenated material sufficiently distant from said first position that substantially no neutrons emitted by said source when in said first position reach said second neutron detecting means;
• thermal neutron stopping means surrounding said second block of hydrogenated material;
• and
• processing means for processing the outputs of said first and second neutron detecting means during a first period of time when said source is maintained at said first position and during a second period of time when said source is maintained at said second position, said processing means utilizing said outputs to determine the number of prompt neutrons produced during said first time period and the number of delayed neutrons produced during said second time period as the result of fissions induced in said fissile material by neutrons emitted by said source during said first time period.