Standard neutron field. 2-1

When the experiment and the theory are compared concerning neutron groups, simple comparison of interaction is meaningless without the establishment of neutron field as sufficient information source. As thermal neutron field, it is the easiest way to make the field of thermally equilibrated neutrons or presenting Maxwell distribution. The heavy water facility is the most excellent among several examples. As medium speed neutron or epithermal neutron field, 1/E region of the reactor spectrum is employed. In this case, thermal neutrons are usually cut with cadmium plates. For the standard field of fast neutrons, nuclear fission spectrum is the best. It is most stable as reference spectrum though there is slight difference according to the nuclides and the incident neutron energy. Though the cadmium filter for cutting thermal neutrons is well known, the neutron field using gadolinium filter also provides the field close to the standard by utilizing the difference between cross section energy. There are crystal monochromator and velocity selector is a sense of extracting the neutrons having a certain energy, which are a little different from the standard field concept. (Wakatsuki, Y.)