Fission spectrum

Han, a. and Elkind, M.M. (1979). TVansformation of mouse C3H lOTl/2 cells by single fractionated doses of x rays and fission-spectrum neutrons, Cancer Res. 39,123. 

Hill, C.K., Han, A., and Elkind, M.M. (1984). Fission-spectrum neutrons at a low dose rate enhance neoplastic transformation in the linear, low dose region (0-10 cGy), Int. J. Radiat. BioL 46 11. 

In nuclear weapons effects studies the fission spectrum anticipated and the materials considered are such that the photoelectric and Compton effects are the most important. In both of these effects electrons are ejected with energies comparable to the energy of the inci-... 

Fig 25 The Effects of Gamma-Ray 235U Fission Spectrum Neutron, and Combined Gamma-Ray and Neutron Irradiation on Whole Crystals of Ammonium Perchlorate Thermally Decomposed at 227° (Ref 224)... 

Cannot be measured because of masking by 252 f spontaneous fission spectrum, e... 

The prior presence of " Pu, the only transura-nic nuclide known to have been present in the early solar system, can be inferred from its spontaneous-fission decay branch, through production of fission tracks and, more diagnostically, by production of fission xenon and krypton. The identification of " Pu as the fissioning nuclide present in meteorites is unambiguous, since the meteoritic fission spectrum is distinct from that of but consistent with that of artificial " Pu (Alexander et al, 1971). The demonstration of the existence of " Pu in the solar system reinforced the requirement (from the presence of I) of a relatively short time between stellar nucleosynthesis and solar-system formation and made it incontrovertible, since while it might be possible to make in some models of early solar system development, the rapid capture of multiple neutrons (the r-process) needed to synthesize Pu could not plausibly be supposed to have happened in the solar system. 

Fission yields of the stable and long-lived isotopes of xenon, cesium, barium, cerium, neodymium, samarium, krypton, rubidium, strontium, zirconium, molybdenum, ruthenium, have been measured mass spectro-metrically for the thermal neutron fission of U23B (40, 61, 90), U233 (4, SI, 61, 82, 100), and Pu239 (32, 61, 66, 124). In addition, the relative yields of the xenon and krypton isotopes produced in the fast neutron fission (fission spectrum neutrons) of U238 and Th232 (64, US) have been determined. 

The isotope is the only spontaneous fission (SF) source of neutrons easily available. It provides fission spectrum neutrons with an average of 2.3 MeV. The characteristics of isotopic neutron sources are given in Table 15.4. 

Effects of Gamma-Ray U Fission Spectrum Neutron, and Combined Gamma-Ray... 

The fission spectrum used by the program is common for all the fissile isotopes and incident energies. It is the Rosen-Cranberg fission spectrum. 

A neutron soure is used to begin the first stage or cycle of any calculation in normal use, the source neutrons are chosen at random from the fission spectrum. In other applications, a source of specified spectrum and angular distribution may be used to start every stage or in some cases the first stage or any stage which becomes extinct. 

The source energy distribution may be sampled from a fission spectrum or a set of energies defining equiprobable ranges. 

A. L. Pope and J. S. Story, Minigal Output from UK Nuclear Data Library—NDLI Thermal Cross-sections, Resonance Integrals and Fission Spectrum Averages, AEEW-M1191 (1973). 

Since the lethargy interval occupied by neutrons is so small, it is often a surprisingly good approximation to assume in fast reactors that all the neutrons have the same energy, Eq, This corresponds to assuming that both the fission spectrum and the kernels H and K are 8-functions in E ... 

Neutrons with energies greater than 0.1 MeV are called fast neutrons. The fission spectrum of a light-water-moderated reactor provides as many fast neutrons as thermal neutrons. Therefore, fast neutron activation of certain elements via (n,p) reactions is a very selective technique, complementary to thermal and epithermal NAA. A typical example is Fe, for which the Fe(n,p) Mn activation reaction produces a better gamma-ray emitter than the thermal capture reaction. 

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