High flux neutron facilities

The choice of the most appropriate scattering technique depends upon two main requirements the contrast factor and/or the need for time-resolved experiments. Presently, time-resolved experiments can be essentially carried out with X-rays thanks to the extremely high flux of photons delivered by synchrotron radiation facilities. In some high flux neutron facilities, such as ILL in Grenoble, some apparatuses allow one to do near-time-resolved experiments under certain experimental setup conditions (low sample-detector distances). 

Institut Laue-Langevin, Neutron Research Facilities at the High Flux Reactor, Institut... 

The very first nuclear reactor built, where the main objective was to perform condensed matter research, was the High Flux Beam Reactor (HFBR) at Brookhaven National Laboratory, Upton, NY. The first self-sustaining chain reaction at the HFBR took place on Halloween, 1965. For over 30 years, the HFBR was one of the premier beam reactors in the world, matched only by the ILL reactor in Grenoble, France. These reactor-based sources have been a continuous and reliable source of thermal neutrons for research in a wide range of different scientific fields from physics, chemistry, materials science, and biology to engineering and isotope emichment. The instrumentation that is in place at these sources has seen steady improvement from the days when Nobel laureates, Brockhouse and Shull, performed their pioneering work at these facilities. 

Neutron Beam Facilities at the high flux reactor, available to users. Institute Laue Langevin, Grenoble, France, (1994). 

The availability of high flux thermal neutron irradiation facilities and high resolution intrinsic Ge and lithium drifted germanium (Ge(Li)) or silicon (Si(Li)) detectors has made neutron activation a very attractive tool for determining trace elemental composition of petroleum and petroleum products. This analytical technique is generally referred to as instrumental neutron activation analysis (INAA) to distinguish it from neutron activation followed by radiochemical separations. INAA can be used as a multi-elemental method with high sensitivity for many trace elements (Table 3.IV), and it has been applied to various petroleum materials in recent years (45-55). In some instances as many as 30 trace elements have been identified and measured in crude oils by this technique (56, 57). 

Neutron sources include nuclear reactors, accelerators, and isotopic sources. Nuclear reactors are, by far, the most frequently used irradiation facilities. They provide high fluxes [upper limit 10 neutrons/(m s)] of mostly thermal neutrons E < I eV). Fast neutrons in the keV range are also available, but at lower flux levels. 

On the other hand, synchrotron X-rays have a distinct advantage, which is the relatively high flux density of radiation. Synchrotron X-ray beams can routinely deliver six orders of magnitude more (monochromatic) X-ray photons (per unit area per unit time) than the best neutron sources available at present. With the advent of free electron laser facilities, the flux difference is expected to grow even larger. 

The most practical neutron source for NAA is a nuclear reactor, which produces neutrons via the nuclear fission process (see Chap. 57 in Vol. 6). Many research reactors are equipped with irradiation facilities that provide a stable, well-tailored, isotropic neutron field with sufficiently high flux. Low-energy (thermal) neutrons comprise the most important part of the reactor spectrum hence the degree of moderation is an important parameter. The irradiation channels are usually created in moderator layers, such as a thermal column or a Be reflector blanket. 

For the reactor route, the saturation yield of Cu from the Zn(n,p) reaction at BOB is 4.14 0.37 GBq mg (112 10 pCi mg ) of Zn at position no. 5 in the High Flux Isotope Reactor (HFIR) hydraulic tube (reactor midplane). Production data and fast neutron fluxes available in irradiation facilities in HFIR and the High Flux Beam Reactor (HFBR, this reactor was permanently shut down in 1999) are summarized in Table 38.8. 

A method for determining the reactivity of highly sub-critical systems of fissile material, u ng neutron-noise power spectral densities in conjunction with a %f source, had previously been tested in two fast reactor critical assemblies (a mockup of the Fast Flux Test Facility reactor and unreflected enriched uranium metal assemblies ) and one thermal reactor (a light water moderated and reflected lattice of Oak Ridge Research Reactor ftiel elements. The last-mentkmed test demonstrated the effectiveness of the method in watermoderated systems and thereby prompted the prexnt study, of its application to facilities for fuel preparation, reprocessing, and storage. 

To illustrate other detrimental effects of low-dose irradiation, the results of some post-irradiation creep experiments performed in air at 550°C on 316L(N) steel specimen are presented in Ref. [44] (Fig. 17.15(b)). The irradiation was carried out in a high flux reactor at Petten s facilities. A neutron fluence of about 0.1 dpa was reached within 600 h. The consequent decrease of creep resistance is clearly visible in Fig. 17.15(b). Finally the question remains as to the relevance of the creep test on irradiated material as compared to creep test under irradiation. 

If high fast-neutron fluxes are available, the sensitivity of Be and B analysis using reactions (2) and (4) is good and, in the absence of facilities for charged particle activation, may be of value. However, the fast-neutron fluxes generally available at the rabbit irradiation positions of many small reactors is too low to be of use. 

Unlike X-rays, which can be produced in a laboratory, neutrons are only available in sufficient quantities at large facilities. Two main types of such facilities must be distinguished, reactor sources and spallation sources, because they have completely different characteristics in high-pressure experiments. The principle of reactor sources need not be described since they are by far the most common sources and have been used for several decades for solid-state studies. The flux from a reactor is usually continuous— the pulsed DUBNA source is an exception—and reactor fluxes are used mainly in the monochromatic angle dispersive mode (as ADXD) for X-ray diffraction. 

How do you find the distance between the hydrogens in these structures to determine if they are dihydrogen or hydride complexes The definitive method is neutron diffraction from a large crystal. Our structures were determined by Tom Koetzle and co-workers at Brookhaven at the high neutron flux reactor. There are only a few places left in the world to do this now that the Brookhaven National Laboratory facility has been closed. Typically dihydrogen ligands have large ther-... 

ITER is the result of a 1987 agreement, a joint research enterprise for the design of an experimental fusion reactor, supported by the EU, the USA, Japan and by the Community of Independent States. Before getting to this stage, it is firstly necessary to develop and test materials which can withstand a very high neutron flux, with the principal aim not to generate an excessive decay power (DeMarco, 2001). In order to cope with these needs, it has now been decided to build a dedicated experimental facility, the International Fusion Materials Irradiation Facility (IFMIF), based on the Li(d, n) reaction. 

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