31. Even comparatively low speed thermal neutrons cause neutron activation ( in fact, they cause it more efficiently ). 32. The HB-2 thermal neutron beam tube is situated radially relative to the reactor core, looking directly at the fuel. 33. White neutron beams also have some measure of uncertainty in their energy spectrum, often with high thermal neutron content. 34. "Cold neutrons " are thermal neutrons that have been equilibrated in a very cold substance such as liquid deuterium. 35. The need for fluorine arose from the need to separate the thermal neutrons ), whereas the latter is not. 36. This means that it can be split into two or three fragments ( fission products ) by thermal neutrons . 37. This leads to buildup of heavier actinides and lowers the number of thermal neutrons available to continue the chain reaction. 38. Plutonium is fissionable with both fast and thermal neutrons , which make it ideal for either nuclear reactors or nuclear bombs. 39. It has significant thermal neutron cross section for fission, but is more likely to capture a neutron and become Pu-239. 40. This discussion focuses on thermal neutron imaging, though much of this information applies to cold and epithermal imaging as well.
