The predecessor group to the NNDC was founded in 1951 when a group known as the Brookhaven Neutron Cross Section Compilation Group was formed at the Brookhaven National Laboratory.
22.
1967 saw the two groups merge into the National Neutron Cross Section Center ( NNCSC ), with Dr . Sol Pearlstein as acting director, officially being appointed Director of the NNCSC in 1968.
23.
However, this simple model does not take into account so called neutron resonances, which strongly modify neutron cross section in energy range of 1 eV 10 keV, nor threshold energy of some nuclear reactions.
24.
On the other hand, for very high energy neutrons ( over 1 MeV ), \ lambda can be neglected, and neutron cross section is approximately constant, determined just by cross section of atomic nuclei.
25.
The isotopes neptunium-235,-236, and-237 are predicted to be fissile; Calculated values of the critical masses of neptunium-235,-236, and-237 respectively are 66.2 kg, 6.79 kg, and 63.6 kg : the neptunium-236 value is even lower than that of plutonium-239 . In particular 236 Np also has a low neutron cross section.
26.
Even though the thermal neutron cross section of 6 Li is low compared to 3 He ( 940 barns vs . 5330 barns ), the atom density of 6 Li in the fiber is fifty times greater, resulting in an advantage in effective capture density ratio of approximately 10 : 1.
27.
The Chart of the Nuclides, containing information such as masses, relative abundances, half-lives, neutron cross sections, and decay properties for more than 3, 100 nuclides and 580 isomers was developed at KAPL . This chart is a necessity for students and professionals in nuclear physics, chemistry, engineering, and medicine around the world.
28.
Although U-238 will not undergo fission by the neutrons released in fission, thermal neutrons can be captured by the nucleus to transmute the atom into Pu-239 . Pu-239 has a neutron cross section very similar to that of U-235, and most of the atoms created this way will undergo fission from the thermal neutrons.
29.
Walter Zinn did not want a woman involved in the dirty work of placing the graphite blocks, but Woods had plenty of work to do with the detectors and thermocouples, and used a small stack of graphite of her own to measure the effects of a radium-beryllium source on manganese foil to obtain a measure of the neutron cross section in order to calibrate the detectors.
