Neutron measurement

The density and thermal neutron cross-section values in Table 6 pertain to the thermal neutron attenuation gauging process. In this method, advantage is taken of the large thermal neutron scattering cross-section of hydrogen as compared to most other elements. In its simplest form, when a beam of thermal neutrons of intensity IQ traverses a sample of thickness x, the intensity 1 of neutrons measured by a thermal neutron detector will be... 

Figure 5. Comparison of phonon DoS neutron measurements [34] (symbols) with PC spectra for NbB2 and TaB2 [33] after subtraction of the rising background (solid curves). The dotted curve in the left panel shows the PC spectrum of ZrB2 [33] for comparison.

These revolutionary ideas lead to further neutron measurements of the structure of zeolite A, which have confirmed the correctness of the traditional 4 0 ordering scheme.58 59 Neutron diffraction traces for several samples of a dehydrated Na zeolite A with Si to A1 ratios of 1.03, 1.09 and 1.12 failed to show any rhombohedral distortions similar to those reported in ref. 57, and in each case the data was consistent with a cubic structure.58 Neutron diffraction experiments on a T1 exchanged sample of the same Na zeolite that had shown the rhombohedral distortion in ref. 57 showed that the crystals now had cubic symmetry59 60 and therefore the distortion that had been measured for the Na zeolite A must be very sensitive to the identity of the exchangeable cations. Profile refinement of this neutron data56 57 also showed a pronounced bimodal distribution of the bond lengths as would be predicted by the 4 0 model. In conclusion it appears that the chemical shifts observed in the n.m.r. experiments can be influenced by factors such as local strain, as well as by the local environment of each Si atom. 

Korff, S. A., Danforth, W. E., Neutron Measurements with Boron-Tri-... 

The structural correlations are strongly enhanced in the under-cooled state as the temperature is reduced towaids the metastable limit of -40°C (to D2O) and various thermoph ical properties exhibit diverged behaviour [8]. The exact nature of this anomaly is still the subject of some controversy. However, the difiraction pattern indicates that the stmcture is evolving towards that of amorphous ice which is characterised as a continuous random networit of tetrahedral hydrogen-bonds [9]. Recent neutron measurements on amorphous ice [10] have re-infor the earlier conjectures tuid shown that the structure is similar to that of hyper-quenched glassy water produced by rapid cooling of micron-sized water droplets. It can now be realised that the CRN mo l for the disordered phase of ice is effectively the limiting stmcture of water at low temperatures. 

In this article, we have presented a series of LD and MD simulations for ice Ih using a variety of water potentials and the results were compared with INS measured DOS. Neutron measurements were shown to provide unique information on the fundamental intramolecular and intermolecular modes, some of which cannot be obtained from the standard IR and Raman techniques. A full knowledge of the intermolecular vibrations as modulated by the molecule s environment in the lattice systems is necessary for a complete analysis of the dynamics of these ice structures. Equipped with the precise knowledge of the structural information obtained by the diffraction measurements [81,82], one can model the system rigorously with suitable force fields or potential functions. The extensive simulation results show that classic pair-wise potentials were unsuccessful in reproducing the measured DOS for ice Ih. 

Highly sensitive He-3 detectors and fission chambers with moderator. Neutron measurements. 

Nuclear and pion related 7-rays provide important information about the spectra of protons and ions accelerated in solar flares [e.g. Hua and Lingen-felter, 1987 Murphy et al., 1987 Lockwood et al., 1997 Hua et al., 2002], However, nuclear 7-ray lines probe the proton spectrum only up to 40 MeV, while 7-rays from pion decays are only observed in the most intense flares. In addition, any spectral break in the proton spectrum is likely to he below the pion production threshold. Neutrons produced at the solar surface over a wide range of energies may provide important information from the 50-300 MeV regime, complementing 7-ray observations. Due to the long neutron thermal-ization time ( 100 s) the 2.223 MeV neutron capture line is only a limited measure of neutron production. The spectrum of accelerated and interacting protons can be deduced more reliably from direct neutron measurements. 

Stable set-up and accurate incident intensity monitoring. The data are normalized by incident intensity. It is important that the incident beam and detector characteristics do not change in an uncontrolled way during the experiment, or that this can be corrected, e.g. by monitoring the incident beam intensity as is done at synchrotron X-ray and spallation neutron measurements. 

For neutron measurements, the requirement of short-wavelength really limits experiments to time-of-flight spallation neutron sources. Reactor sources with hot moderators would give good quality data for PDF studies, but are in short supply. The requirements for a spallation neutron powder diffractometer are laid out in the list of experimental requirements above. Normal t-o-f powder... 

SAHAGIA, M., et al., The standardization of "Lu and its use in nuclear medicine, neutron measurements evaluation and apphcations , paper presented at NEMEA 2, EC-JRC-IRMM Conf, Bucharest, 2004. 

Phys. Chem., 96, 22-24. Neutron inelastic scattering spectrum of footballene C6o-R.L. Capjjelletti, J.R.D. Copley, W.A. Kamitakahara, F. Li, J.S. Lannin, D. Ramage (1991). Phys. Rev. Lett., 66, 3261-3264. Neutron measurements of intramolecular vibrational modes in Cjo-... 

From the distribution of the intensity in the reciprocal space (2kp planes), the polarization of this modulation is found to have two components a longitudinal component in chain direction and a transvBrsB component in c" direction which corresponds to the direction of tilt of the molecules. Inelastic neutron measurements reveal, in thB samB temperature range, an anomaly in the transverse modB with main polarization along c" (figure 3). It is this fluctuation which diverges at the Peierls transition at 54 K. 

Phase 3. Carry out neutron measurements on a working 4-stack PEM fuel cell to define the operating parameters of the new setup and test the limits of achievable spatial and temporal resolution of water distribution and flow dynamics inside a working fuel cell. 

The factor k /ko present in (8.9) arises from the fact that the flux of neutrons measured at the detector depends on the velocity of the neutrons. Equation (8.10) can be derived from equation (8.9) by letting k = ko, by eliminating the time dependence of r/f), and by recognizing that... 

Two source effects are discussed in this section absorption of particles in the source, and the effect of the backing material that supports the source. Both effects are always important in measurements of charged particles. In some cases, however, they may also be significant in X-ray or thermal-neutron measurements. 

From the mass yield curve in Figure 14.9 we leant that conqjlementary fission products (i.e. the two products Aj and A2 with identical yield values symmetrically located around the minimum) add up to about 234, not 236. Direct neutron measurements reveal that on the average 2.5 neutrons are emitted in fission of U by thermal neutrons. This number increases as the Z of the tarcet and as the bombarding energy increases. 

CP or T violation divide into (a) those that involve weak interactions or parity violation, and (b) those that involve processes otherwise allowed by the strong or electromagnetic interactions. In class (a) the most sensitive are probably the searches for an electric dipole moment of the neutron, measured to be < 1.0 X 10 e cm, and the electron (—0.18 0.16) x 10 e cm. A nonzero value requires both P and T violation. Class (b) includes the search for C violation in r] decay, believed to be an electromagnetic process, e.g., as measured by r( 7 all) < 5 x 10 , and searches for T... 

Interdiffusion between a pair of polymers is a demonstration of their thermodynamic miscibility. The adhesion between contacted rubber sheets parallels the extent of any interdiffusion of the polymer chains (Roland and Bohm, 1985). If the contacted sheets are comprised of immiscible rubbers, no interdiffusion occurs. Natural rubber (NR) and 1,2-polybutadiene (1,2-BR) are miscible even at high molecular weights (Roland, 1988a Roland, 1987). When NR is brought into contact with 1,2-BR, they interdiffuse spontaneously. When some form of scattering contrast exists between the materials, interdiffusion will enhance the scattering intensity (either X-ray or neutron) measured from the plied sheets. A variety of spectroscopic methods (Klein, 1981 ... 

Neutron measurements (pulses and wide range current)... 

The only other American scientist at the meeting besides Briggs was Mohler. He may have concurred with Roberts, but Roberts had the necessary fast-neutron measurements. 

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