Neutrons, from nuclear reactors

C. Rietveld performs crystal structure refinement and quantitative phase analysis using powder diffraction data and the Rietveld method. Combining refinement programs and advanced modeling tools allows a faster route to determining the structures of both inorganic and molecular crystals. An effective way to know the atomic structure is by means of diffraction techniques using neutrons from nuclear reactors and particle accelerators or X-rays from... 

Early studies (1936-1950) of neutron scattering used radium-beryllium neutron sources but their low neutron flux prevented exploitation of neutron scattering as a spectroscopic technique [4]. Today neutrons are either extracted from a nuclear reactor or generated at a pulsed, accelerator-based spallation source. The exploitation of neutrons from nuclear reactors in structural studies and spectroscopy dates from the 1950s and from pulsed sources from the 1970s. A useful summary of the development of neutron sources is given in [5]. 

Production-Scale Processing. The tritium produced by neutron irradiation of Li must be recovered and purified after target elements are discharged from nuclear reactors. The targets contain tritium and He as direct products of the nuclear reaction, a small amount of He from decay of the tritium and a small amount of other hydrogen isotopes present as surface or metal contaminants. 

The products of nuclear fission reactions are radioactive and disintegrate according to their own time scales. Often disintegration leads to other radioactive products. A few of these secondary products emit neutrons that add to the pool of neutrons produced by nuclear fission. Very importantly, neutrons from nuclear fission occur before those from radioactive decay. The neutrons from nuclear fission are termed prompt. Those from radioacth e decay arc termed delayed. A nuclear bomb must function on only prompt neutrons and in so doing requires nearly 100 percent pure (or Pu) fuel. Although reactor... 

Neutron depth profiling technique (NDP) [13]. NDP is a speeial method for depth profiling of few light elements, namely He, Li, B and N in any solid material. The method makes use of speeifie nuelear reaetions of these elements with thermal neutrons. The samples are plaeed in the neutron beam from nuclear reactor and the charged products of the neutron indueed reactions (protons or alpha particles) are registered using a standard multiehannel spectrometer. From the measured energy spectra the depth profiles of above mentioned elements can be deduced by a simple computational procedure. 

NEPTUNIUM. [CAS 7439-99-8]. Chemical element, symbol Np, at. no, 93, at. wt, 237,0482 (predominant isotope), radioactive metal of the Actinide series, also one of the Transuranium elements. Neptunium was the first of [he Transuranium elements [o be discovered and was first produced by McMillan and Abelson (1940) at the University of California at Berkeley. This was accomplished by bombarding uranium with neutrons. Neptunium is produced as a by-pruduct from nuclear reactors. 237Np is the most stable isotope, with a half-life of 2.20 x 106 years, The only other very long-lived isotope is that of mass number 236. with a half-life of 5 x 10- years. 

Although thermal (slow) neutrons derived from nuclear reactors are the most practical source of particles for nuclear excitation and generally provide the more useful reaction, other excitation sources, such as 14-MeV (fast) neutrons from commercially available accelerators or generators, have also been applied to coal analysis. 

Wieczorek, H. 1988. Method of reprocessing boron carbide irradiated with neutrons from trim of shut-down elements from nuclear reactors. U.S. Patent 4793983. 

Neutron beams may be extracted from nuclear reactors, and samples may be inserted into the beam outside the reactor, where the background radiation is sufficiently reduced to allow measurement of the activity generated in the sample to be made during irradiation. 

As laid out in the Equation 21.1 definition of /c-effective, the basic neutron balance relationship is between fission neutron production and neutron loss mechanisms, the two neutron loss mechanisms being neutron absorption and neutron leakage. Nuclear reactors, for which criticality must be created and maintained for extended periods, tend to be large devices—both for neutron balance reasons and because of the large fuel inventory required to deliver substantial amounts of power for long periods of time. The result of this, from the point of view of the A -effective equation, is that neutron leakage is a relatively unimportant neutron... 

Highlights. Treatment of the radioactive waste from nuclear reactors is one of the points that receive wide public attention and the disposal and burial of HLW in particular is a contentious issue due to the concerns about leakage to the environment. The technical solutions that are currently used to treat the waste that were listed earlier (concentrate-and-contain, dilute-and-disperse, and delay-and-decay) are not suitable for HLW, where safer solutions like vitrification or Synroc are sought. The characterization of the LLW and MLW waste is not as complicated as that of spent fuel but stiU greatly more complex than analysis of fresh fuel. Some of the procedures and methods used in other parts of the NFC are suitable for LLW and MLW. The composition of HLW must be determined in order to estimate the decay rate of the radioactivity and to classify the required protective measures that depend on the radionuclides and their products (emitters of alpha, beta, gamma, and neutrons). 

Fission fragments, the waste products from nuclear reactors, emit j3 particles, neutrons, and y radiation and will remain lethal for at least 500 years. 

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