NEUTRONIC ANALYSES

Although these effects are small, they affect not only the covalent X-H bond lengths, but also the H - A hydrogen-bond lengths. For very high-precision low-temperature neutron diffraction analyses [186, 187], they have to be taken into account. An adequate way to do this, without the complexity of a complete anhar-monic thermal motion analysis, is to use the experimentally determined anisotropic temperature factors. As shown by comparisons between experimental and theoretical X-H values from low temperature neutron analyses and theoretical ab-initio molecular orbital calculations, one can assume that the motion of the two... 

The cyclic oligosaccharides, a-, and y-cyclodextrins crystallize well. A large number of X-ray structure analyses and three neutron analyses of the hydrates and inclusion complexes of these molecules have been reported. These interesting structures, which are midway between biological small molecules and macromolecules, are discussed separately in Part III, Chapter 18. 

The neutronic analyses of these disrupted cores show that the reactivity changes from separation processes dominate those from compaction. Both compaction and separation lead to the highest reactivity increases in the U-free core. For this latter cote, a criticality problem is identified and can be more pronounced at high temperature if PuN decomposition is assumed. In the case of complete decomposition and Pu-pure configurations, the masses leading to criticality ate reduced by a frictor of two. 

The Monte Carlo N-Particle (MCNP) (version 4C2) code was used for most of the neutronics analyses by both organizations. 

Updated neutronics analyses were performed at SNL to better match the reference AHTR geometry and fliel/coolant fractions. As before, the fuel type was TRISO-coated particle fuel with a particle packing fraction of 30% in the fuel compacts. All of the calculations were performed with 1200 K neutron cross-sections, and the thermal scattering function, S(a,P), was also used at 1200 K for the carbon in the fuel compacts and prismatic matrix. 

Core dimensions and fuel volume fraction from the core neutronics analyses ... 

The resonance absorbers provide negative feedback because of Doppler broadening of the resonances. As mentioned above, the resonance absorbers may be tungsten, dysprosium, iridium, europium, erbium, and other rare earth metals with resonances in the eV to tens of eV range. Specific neutronic analyses performed to obtain the temperature coefficient of reactivity and quantities needed in the fuel alloy are under way for several of the candidate resonance absorbers. 

The maximum reactivity worth of a CR cluster depends on the loading pattern of the fuel assemblies and the CR pattern. Any limitation of the loading pattern or any interlock of the CR pattern, like the rod worth minimizer of BWRs, is not considered conservatively. From core neutronics analyses, the highest reactivity worth of a CR cluster under all the considerable loading patterns and CR patterns is estimated as 1.05%dk/k at the normal operating condition and 2.8%dk/k at the hot... 

The investigation into the sabotage of Pan Am Flight 103, which left 269 dead, indicated that the explosive used was Semtex H, a plasticized mixture of hexahydro-l,3,5-trinitro-s-triazine and pentaerythritol tetranitrate, and that the amount used was half the quantity that the fledgling technique of Thermal Neutron Analysis (TNA) was designed to detect. Although the placement of the explosive device was fortuitous (from the terrorists point of view) and the suitcase had not been screened by TNA, this event killed the TNA prototype program. 

M. J. Hurwitz, W. P. Noronba, T. A. Atwell, Airport Testing of a New Thermal Neutron Analysis Explosives Detection System, Proceedings of the First International Symposium on Explosive Detection Technology, pp. 388—395, 13—15 November 1991. US Department of Transportation, February 1992. 

D. R. Brown, Cargo Inspection System Based on Pulsed Fast Neutron Analysis An Update, SPIE Vol. 2276, Cargo Inspection Technologies (1994) 449. 

D. R. Brown, T. Gozani, R. Loveman, J. Bendahan, P. Ryge,J. Stevenson, F. Liu, M. Sivakumar, Application of Pulsed Fast Neutrons Analysis to Cargo Inspection, Nuclear Instruments and... 

Terrorism and Drug Trafficking Testing Status and Views on Operational Viabihty of Pulsed Fast Neutron Analysis Technology, Report to the Subcommittee on Treasury and General Government, Committee on Appropriations, US Senate, GAO/GGD-99-54, April 1999. 

The 1985 tragedy of Air India Flight 182, which exploded off Ireland en route from Montreal to London, stimulated an intensified effort to thwart terrorists. The International Security and Development Act of 1985 provided for air marshals and expanded FAA s R D for airport security. Thermal neutron analysis (TNA) and a number of sniffer technologies for trace explosives detection, which had been developed under FAA sponsorship, were accelerated toward commercial production. 

N(5) is apparently H bonded to the keto 0 (6) of an adjacent molecule. The H s on N(4> bond this atom to three Cl ions. The remaining short approaches are apparently not due to H-bonding. A neutron analysis of this structure would be very advantageous. 

Most reliable are the data on neutron fluxes which are determined by the plasma power density, reactor geometry and structural parameters. Most of the conceptual power reactor design studies contain a detailed neutronics analysis giving the energy as well as the spatial distribution of neutron fluxes. 

One of the most developed of these methods is the technique usually referred to as pulsed fast neutron analysis (PENA) [3,11-13], The operation is illustrated in Fig. 7 [11], Neutrons in the range of 8 MeV are generated by an accelerator (not shown) by the reaction D(d,n)He. The accelerator is pulsed with a 1 ns pulse width to produce 1 ns pulses of neutrons with a repetition rate of 1 MHz. Gamma rays are detected in a series of scintillation detectors. The time difference between the accelerator pulse and the... 

Fig. 5. Spectra from pulsed neutron analysis of coal.

Fig. 14. Geometry for fast neutron analysis showing single source and single detector.

Fig. 15. Variation of sensitivity with position for fast neutron analysis. Distances in centimeters.

Even assuming that these limitations are acceptable, the most appropriate and promising techniques for security applications are based on nanosecond neutron analysis (not only in API) therefore, the use of HPGe with its intrinsically slow signal (timing resolutions of tens of nanoseconds at best) and low-rate capability is highly undesirable. The use of HPGe in this application with 14-MeV neutron sources has been described in the literature for more than 15 years with little evidence that such detectors improve real-world system performance and much evidence that they do not. 

API, associated particle interogation FNA, fast neutron analysis PFNA, pulsed fast neutron analysis TNA, thermal neutron analysis. 

W.C. Lee, D.B. Mahood, P. Ryge, P. Shea and T. Gozani, Thermal neutron analysis (TNA) explosive detection based on electronic neutron generators, Nucl. Instrum. Methods Phys. Res. Sec. B, 99(1 1) (1995) 739-742. 

Panel on Assessment of the Practicality of Pulsed Fast Neutron Analysis for Aviation Security, National Research Council, Assessment of the Practicality of Pulsed Fast Neutron Analysis for Aviation Security, National Academies Press, Washington (2002)... 

P.C. Womble, G. Vourvopoulos, J. Paschal and P.A. Dokhale, Multi-element analysis utilizing pulsed fast/thermal neutron analysis for contraband detection, Proc. SPIE, 3769 (1999) 189-195. 

As indicated above, in evaluating < >res> the averaging was performed only between 39.9 kJ/mol and 9.75 MJ/mol since the majority of the interactions involving transplutonium nuclides occur in this interval further, it was a sub-grouping readily available to us from the complete reactor neutronic analysis. 

Three-center bonds can be symmetrical with r3 r2, 0 02 and asymmetrical, in which rt and r2 differ by as much as 1.0 A, 0t is close to 180° and 02 is close to 90°. Examples of these have been well established by the neutron diffraction studies of the amino acids [60, 74] and the pyranose sugars [58]. A case where the decision between two- and three-centered bonding is difficult is illustrated from the neutron analysis of erythritol [77], shown in Fig. 2.3. Although one bond is much longer than the other, both are primarily electrostatic. It is difficult to refer to one as a hydrogen bond and the other as an electrostatic attraction. In this monograph, we call these the major and minor component of a three-center bond. 

Thble 9.3. Intramolecular inter-residue OH - O hydrogen bonds in disaccharides. These hydrogen bonds are frequently three-centered. When one of the components is intermolecular, the distance is indicated bya. With the exception of the neutron analysis, (N), the O-H covalent bond lengths have been normalized to 0.97 A... 

Table 14.1. REFCODES for crystal structure analyses of commonly occurring amino acids and their hydrochlorides and hydrates (n = neutron analysis)... 

Neutron analysis of a five-coordinate H (/u. -H) atom has also been reported, located in two sqnare pyramidal positions of the [H2Rhi3(CO)24] metal cluster anion. As in the case of the Co-H series, a similar trend was noticed in Rh-H distances increasing as a function of the number of metal atoms around the H atom. 

In principle the reaction could conceivably proceed four ways two different ways of cis addition of D and OD, and two ways of transaddition, leading to four potential products. The results of our neutron analysis, which was carried out... 

Water Extraction by ion-exchange dissolution in low oxygen solvent irradiation Delayed neutron analysis (total uranium) 0.4 pg/L No data Zielinski and McKown 1984... 

Zielinski RA, McKown DM. 1984. Determination of uranium concentration in water by liquid anion-exchange-delayed-neutron analysis. J Radioanal Nucl Chem 84 207-212. 

The homogeneity has been checked at three occasions once prior to the intercomparison work and the first part of the certification, once after the ampouling prior to the second part of the certification, and once at the stage of the F and Cl certification. The first series of tests were carried out by instrumental neutron analysis (INAA). Samples were irradiated with thermal neutrons in a tube container for 10 min, or for 40 h when mounted on a turntable. In the first case the neutron flux was kept constant. 

Nuclear or thermal neutron analysis One application uses californium (a radioactive element) to excite explosive material to release gamma rays that can be detected. Another application excites hydrogen in an explosive that releases neutrons that can be detected. Early in development. Has a small footprint. Hydrogen sensors are not effective in moist soil. 

Advanced sensor technologies with application to detection and clearance can be grouped as follows infrared sensors, ground-penetrating radars, microwave, photon backscatter, nuclear or thermal neutron analysis, and lasers. Their characteristics were summarized in Table 12.1. 

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