Project Y: the Los Alamos Story - David Hawkins
David Hawkins - Project Y: the Los Alamos Story, p.89.
An example of theoretical influence on experimental design was the "Feynman experiment," which was never performed but whose principle was embodied in several experiments. This was the proposal to assemble near-critical or even supercritical amounts of material safely by putting a strong neutron absorber (the B-10 boron isotope) uniformly into the core and tamper. An absorber whose absorption cross section was inversely proportional to the velocity of the neutrons absorbed would decrease the multiplication rate in the system by an amount directly proportional to the absorber concentration. Thus a supercritical material could be made subcritical by adding boron. By measuring the rate at which the neutron died out in this system, one could calculate the rate at which it would increase if the boron were absent.
An example of theoretical influence on experimental design was the "Feynman experiment," which was never performed but whose principle was embodied in several experiments. This was the proposal to assemble near-critical or even supercritical amounts of material safely by putting a strong neutron absorber (the B-10 boron isotope) uniformly into the core and tamper. An absorber whose absorption cross section was inversely proportional to the velocity of the neutrons absorbed would decrease the multiplication rate in the system by an amount directly proportional to the absorber concentration. Thus a supercritical material could be made subcritical by adding boron. By measuring the rate at which the neutron died out in this system, one could calculate the rate at which it would increase if the boron were absent.