21. In addition to the regular fuel assemblies, there are instrumented ones, containing neutron flux detectors in the central carrier. 22. The neutron flux involved may be on the order of 10 22 neutrons / ( cm 2 �second ). 23. The High Flux Isotope Reactor built in 1965 with the highest neutron flux of any reactor at the time. 24. The sources are therefore positioned so the neutron flux they produce is always detectable by the reactor monitoring instruments. 25. Historians can use accidental neutron activation to authenticate atomic artifacts and materials subjected to neutron fluxes from fission incidents. 26. The latter isotope is produced instead in a process where 239 Pu captures four neutrons under high neutron flux : 27. Within a nuclear fission reactor the neutron flux is primarily the form of measurement used to control the reaction inside. 28. The sample and a standard are then packaged and irradiated in a suitable reactor at a constant, known neutron flux . 29. Polonium may now be made in milligram amounts in this procedure which uses high neutron fluxes found in nuclear reactors. 30. These holes allow inserting special holders containing flux wires into the core, to obtain neutron flux maps of the core.
