Calculation and study of 14 MeV neutron attenuation coefficients in a double axis rotational system

The neutron attenuation coefficient is determined in a double axis rotational system. The difference between a fixed system and a double axis rotational system is shown and curves for the neutron attenuation coefficient for the last case are drawn. The attenuated flux inside the sample is also drawn.     

Comparison of experimental and computational neutron spectroscopy at a 14 MeV neutron generator facility

At any neutron production facility, the energy spectrum at any meaningful distance from the target will be modified. For the case of a facility used to provide reference irradiations of electronics and other devices at various target-to-device distances it is important to have knowledge of these spectral modifications. In addition, it is desirable to have the ability to generate near real-time measurement capability. Advances in neutron metrology have made it possible to determine neutron energy spectra in real time to high levels of accuracy. This paper outlines a series of experimental measurements and theoretical calculations designed to quantify the scattering effects for a 14 MeV neutron generator facility, and makes appropriate recommendations for near real-time measurements of these fields.     

On-stream nuclear activation of trace uranium and thorium using a 14 MeV neutron generator

A method for the continuous on-stream determination of trace concentrations of uranium and thorium in flowing streams is developed. The 14 MeV neutron generator was used for irradiation and the delayed neutron counting technique was employed in counting the induced neutron activity. The dependence of the minimum detectable concentration on the irradiation, decay and counting times, liquid flow-rate and the background was studied. At optimal conditions, uranium and thorium concentrations were determined down to 20 and 100 ppm, respectively. The interference of the neutron emitting nuclide^17m O was reduced to an insignificant level by optimizing the decay time.     

In situ high-throughput study of drug polymorphism under controlled temperature and humidity using FT-IR spectroscopic imaging

Fourier transform infrared (FT-IR) spectroscopic imaging in combination with a controlled humidity cell was applied to simultaneously monitor crystallisation of several binary mixtures of two drugs under identical environment. The effect of relative humidity was studied on samples of binary mixtures of nifedipine and nitrendipine with different molar ratios as well as on amorphous nitrendipine. All samples were arranged in array format on the surface of BaF₂ window for simultaneous imaging using an infrared focal plane array detector. The effect of sample thickness on the analysis of imaging results was addressed using novel approach to create images. The thickness-independent images have been obtained by plotting the distribution of the wavenumber corresponding to the peak maximum of the ν(NH) vibrational mode which is sensitive to the formation of the various crystalline polymorphs. The FT-IR spectroscopic imaging approach described in this work can be utilised in further high-throughput studies of many samples under controlled environment.     

Design and construction of a facility for neutron activation analysis using the 14 MeV neutron generator at HMS Sultan

The potential for using a small, sealed tube, DT neutron generator for neutron activation analysis has been well documented but not well demonstrated, except for 14 MeV activation analysis. This paper describes the design, construction and characterization of a neutron irradiation facility incorporating a small sealed tube DT neutron generator producing 14 MeV neutrons with fluence rates of 2·10⁸ s⁻¹ in 4π (steady state) and 10¹¹ s⁻¹ in 4π (pulsed). Monte Carlo modeling using MCNP4c and McBend9 has been used to optimize the design of this facility, including the location of a thermal irradiation facility for conventional neutron activation analysis. A significant factor in designing the facility has been the requirement to conform with Ionising Radiation Regulations and the design has been optimized to keep potential radiation doses to less that 1 μSv/h at the external walls of the facility. Activation of gold foils has been used for flux characterization and the experimental results agree well with the modeling.     

The photoreactions of recombinant phytochrome from the cyanobacterium Synechocystis: a low-temperature UV-Vis and FT-IR spectroscopic study

The interconvertible photoreactions of recombinant phytochrome from Synechocystis reconstituted with phycocyanobilin were investigated by light-induced optical and Fourier-transform infrared (FT-IR) difference spectroscopy at low temperatures for the first time. The photochemistry was found to be deferred below -100 degrees C for the transformation of red-absorbing form of phytochrome (Pr)-->far-red-absorbing form of phytochrome (Pfr), and no formation of an intermediate similar to the photoproduct of phytochrome A obtained at -140 degrees C (lumi-R) was observed. Two intermediates could be stabilized below -40 degrees C and between -40 and -20 degrees C, and were denoted as meta-Ra and meta-Rc, respectively. Above -20 degrees C Pfr was obtained. In the reverse reaction two intermediates could be stabilized below -60 degrees C (lumi-F) and between -60 and -40 degrees C (meta-F). The FT-IR difference spectra of the late Pr-->Pfr photoreaction show great similarities to the spectra obtained from oat phytochrome A suggesting similar conformation of the chromophore and interactions with its protein environment, whereas deviations in the spectra of meta-Ra were observed. A large band around 1700 cm-1 in the difference spectra between the intermediates and Pr which is tentatively assigned to the C19=O group of the prosthetic group indicates the Z,E isomerization around the C15=C16-methine bridge of the chromophore during the formation of meta-Ra. In the difference spectra of the parent states only small differences are observed in this region suggesting that the frequency of the carbonyl group is similar in Pr and Pfr. Since the FT-IR difference spectra between lumi-F and Pfr show great similarities to the spectra of the parent states, it is assumed that during the formation of lumi-F the chromophore largely returns into the primary Pr conformation. The FT-IR spectra recorded in a medium of 2H2O generally show a downshift of the significant bands due to the isotope effect. The appearance of a characteristic band around 935 cm-1 in all 2H2O spectra suggests an assignment to an N-2H bending vibration of the chromophore.     

Elemental analysis of geological samples by cyclic activation using a 14 MeV neutron generator and applying flux corrections

The solvent extraction of the rare earth elements, yttrium and scandium with trioctylphosphine oxide in the presence of strong complexing and various salting-out agents has been studied. As a result, a technique was developed for the extractionchromatography recovery of the rare earth elements and yttrium with simultaneous purification practically from all the elements, including scandium, usually present in the mineral samples.     

CO and NO adsorption on VO x /SBA-15 catalysts: an FT-IR spectroscopic study

The adsorption of CO and NO over VO _x -SBA-15 mesoporous materials with different vanadium content was investigated by FT-IR spectroscopy. Vanadium complexes were reduced in situ by hydrogen atmosphere at 450 °C for 3 h. Spectra of reduced samples show increasing in intensity of silanol groups, caused by dissociation of V–O(Si) bonds and formation of new H–O(Si) bonds. Reduction occurs with formation of water. The band corresponds to overtone of V=O stretching modes decreases in intensity because of oxygen withdrawing from V=O species. Presence of V⁴⁺ and V³⁺ species was observed. Inspection of CO adsorbed IR spectra evidenced existence at least two different type of V³⁺–CO complexes on the silica surface differing in both stretching frequencies and complex stabilities. We did not found principal difference between spectra of absorbed CO at ?196 °C on the samples with different concentration of vanadium, probably because of relative low degree of reduction. As well as heterogeneity of surface V³⁺ and V⁴⁺ species was evidenced by adsorption of NO. Both V³⁺ and V⁴⁺ ions possess two effective coordinative vacancies and as a result can adsorb two NO molecules forming dinitrosyls. A part of V³⁺ cations forms only mononitrosyls characterize by band at 1724 cm^?1. Results obtained after NO adsorption reveal existence of three different kinds of vanadium species. Probably two of them are isolated and associated vanadium sites. The third type of vanadium has different surrounding than other two types. It was demonstrated that NO is a better probe than CO for testing the oxidation and coordination state of reduced vanadium species.     

A switchable molecular rotator: neutron spectroscopy study on a polymeric spin-crossover compound

A quasielastic neutron scattering and solid-state (2)H NMR spectroscopy study of the polymeric spin-crossover compound {Fe(pyrazine)[Pt(CN)(4)]} shows that the switching of the rotation of a molecular fragment--the pyrazine ligand--occurs in association with the change of spin state. The rotation switching was examined on a wide time scale (10(-13)-10(-3) s) by both techniques, which clearly demonstrated the combination between molecular rotation and spin-crossover transition under external stimuli (temperature and chemical). The pyrazine rings are seen to perform a 4-fold jump motion about the coordinating nitrogen axis in the high-spin state. In the low-spin state, however, the motion is suppressed, while when the system incorporates benzene guest molecules, the movements of the system are even more restricted.     

Probing the molecular and electronic structure of capsaicin: a spectroscopic and quantum mechanical study

The conformational preferences of capsaicin were investigated by using the hybrid meta density functional theory (DFT) method MPWB1K. Its flexible, pendant side chain allows for a multitude of conformations only slightly different in energy. The distinctive vibrational features of the most stable conformers were characterized. To elucidate the most favorable reaction sites of capsaicin for radical scavenging, various homolytic bond-dissociation energies were also calculated. Of the possible radical intermediates, the allyl and benzyl radicals are energetically preferred. The filled and empty electronic structures of capsaicin were investigated by exploiting the photoelectron and electron-transmission spectra also of reference molecules and suitable quantum-mechanical calculations. On this basis, a reliable pattern of the vertical ionization energies and electron-attachment energies of capsaicin was proposed. The frontier pi molecular orbitals are concentrated over the vanillyl moiety, with a modest influence of the amidic-aliphatic chain. The (negative) first vertical electron affinity is predicted to be similar to that of benzene. The absorption spectrum of capsaicin and its change by conversion into a phenolic deprotonated anion (modest bathochromic displacement) or a phenoxyl neutral radical (from colorless to red) were interpreted with time-dependent DFT calculations. ESR measurements following chemical or electrochemical reduction of capsaicin did not lead to detection of the corresponding radical anion. The spectra show fragmentation of the original molecule and formation of a variety of radical species which are believed to have a semiquinonic structure.     

Self-assembly of a nonionic photoresponsive surfactant under varying irradiation conditions: a small-angle neutron scattering and cryo-TEM study

We have used small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM) to determine the structure of aggregates formed by the photoresponsive surfactants diethylene glycol mono(4',4-butyloxy, butyl-azobenzene) (C4AzoOC4E2) and diethylene glycol mono(4',4-hexyloxy, butyl-azobenzene) (C4AzoOC6E2) under different illumination conditions. At high concentrations, the self-assembly behavior of these surfactants changes remarkably in response to different radiation conditions. The trans isomers assemble into bilamellar (C4AzoOC4E2) and unilamellar (C4AzoOC6E2) vesicles, while the cis isomers (under UV light) form bicontinuous phases. These light-induced structural changes are attributed to a change in the sign of the Gaussian rigidity, which is the direct result of azobenzene photoisomerization.     

Solvent-dependent modulation of metal-metal electronic interactions in a dinuclear cyanoruthenate complex: a detailed electrochemical, spectroscopic and computational study

The dinuclear complex [{Ru(CN)(4)}(2)(μ-bppz)](4-) shows a strongly solvent-dependent metal-metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH(2)Cl(2). In CH(2)Cl(2) the separation between the successive Ru(ii)/Ru(iii) redox couples is 350 mV and the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mV and the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH(2)Cl(2) or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH(2)Cl(2) and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCT excited state, which is formulated as Ru(III)(bppz˙(-))Ru(II) and can therefore be considered as a mixed-valence Ru(ii)/Ru(iii) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(ii) and Ru(iii) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz˙(-) which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(ii)/Ru(ii), Ru(ii)/Ru(iii) and Ru(iii)/Ru(iii) calculations in both water and CH(2)Cl(2) well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN)(4)(μ-bppz)](2-) and [{Ru(CN)(4)}(2)(μ-bppz)](4-) very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH(2)Cl(2).     

Quasi-elastic neutron scattering study of dimethyl-sulfoxide-water mixtures: probing molecular mobility in a nonideal solution

The translational and rotational motions of water and dimethyl sulfoxide, [DMSO, (CH(3))(2)SO] have been investigated using quasi-elastic neutron scattering. Water-DMSO mixtures at five DMSO mole fractions, chi(DMSO), ranging from 0 to 0.75, were measured. Hydrogen-deuterium substitution was used to extract independently the water proton dynamics (d-DMSO-H(2)O), the DMSO methyl proton dynamics (h-DMSO-D(2)O) and to obtain background corrections (d-DMSO-D(2)O). The translational diffusion of water slows down significantly compared to bulk water at all chi(DMSO)>0. The rotational time constant for water exhibits a maximum at chi(DMSO)=0.33 that corresponds to the observed maximum of the viscosity of the mixture. Data for DMSO can be analyzed in terms of a relatively slow tumbling of the molecule about its center-of-mass in conjunction with random translational diffusion. The rotational time constant for this motion exhibits some dependence on chi(DMSO), while the translational diffusion constant shows no clear variation for chi(DMSO)>0. The results presented reinforce the idea that due to the stronger associative nature of DMSO, DMSO-water aggregates are formed over the whole composition range, disturbing the tetrahedral natural arrangement of the water molecules. As a consequence adding DMSO to water causes a drastic slowing down of the dynamics of the water molecule, and vice versa.     

Supercritical ammonia: a molecular dynamics simulation and vibrational spectroscopic investigation

Combining infrared spectroscopy and molecular dynamics simulations, we have investigated the structural and dynamical properties of ammonia from liquid state (T = 220 and 303 K) up to the supercritical domain along the isotherm T = 423 K. Infrared spectra show that the N-H stretching and bending modes are significantly perturbed which is interpreted as a signature of the change of the local environment. In order to compare the experimental spectra with those obtained using molecular dynamics simulation, we have used a flexible four sites model which allows to take into account the anharmonicity in all the vibration modes particularly that of the inversion mode of the molecule. A good agreement between our experimental and calculated spectra has been obtained hence validating the intermolecular potential used in this study to simulate supercritical ammonia. The detailed analysis of the molecular dynamics simulation results provides a quantitative insight of the relative importance of hydrogen bonding versus nonhydrogen bonded interactions that governs the structure of fluid ammonia.     

Maya blue: a computational and spectroscopic study

Maya Blue pigment, used in pre-Colombian America by the ancient Mayas, is a complex between the clay palygorskite and the indigo dye. The pigment can be manufactured by mixing palygorskite and indigo and heating to T > 120 degrees C. The most quoted hypothesis states that the dye molecules enter the microchannels which permeate the clay structure, thus creating a stable complex. Maya Blue shows a remarkable chemical stability, presumably caused by interactions formed between indigo and clay surfaces. This work aims at studying the nature of these interactions by means of computational and spectroscopic techniques. The encapsulation of indigo inside the clay framework was tested by means of molecular modeling techniques. The calculation of the reaction energies confirmed that the formation of the clay-organic complex can occur only if palygorskite is heated at temperatures well above the water desorption step, when the release of water is entropically favored. H-bonds between the clay framework and the indigo were detected by means of spectroscopic methods. FTIR spectroscopy on outgassed palygorskite and freshly synthesized Maya Blue samples showed that the presence of indigo modifies the spectroscopic features of both structural and zeolitic water, although no clear bands of the dye groups could be observed, presumably due to its very low concentration. The positions and intensities of delta(H2O) and nu(H2O) modes showed that part of the structural water molecules interact via a hydrogen bond with the C=O or N-H groups of indigo. Micro-Raman spectra clearly evidenced the presence of indigo both in original and in freshly synthesized Maya Blue. The nu(C=O) symmetric mode of Maya Blue red-shifts with respect to pure indigo, as the result of the formation of H-bonds with the nearest clay structural water. Ab initio quantum methods were applied on the indigo molecule, both isolated and linked through H-bonds with water, to calculate the magnitude of the expected vibrational shifts. Calculated and experimental vibrational shifts appeared to be in good agreement. The presence of a peak at 17.8 ppm and the shift of the N-H signal in the 1H MAS NMR spectrum of Maya Blue provide evidence of hydrogen bond interactions between indigo and palygorskite in agreement with IR and ab initio methods.     

Ion solvation and association in LiClO4/sulfolane solution: a vibrational spectroscopic and molecular orbital study

Solvation interaction and ion association in solutions of lithium perchlorate/sulfolane have been studied by using infrared and Raman spectra as a function of concentration of lithium perchlorate. The band changes of antisymmetric OSO stretch, antisymmetric CSC stretch, -SO2 wag and twist suggest that there is an interaction between Li+ and sulfolane molecules, and the site of solvation is the oxygen atom of -SO2 group. The molecular orbital calculation supports this suggestion. On the other hand, the apparent solvation number was calculated, and the band fitting for the ClO4- band reveals the presence of contact ion pair, solvent separated ion pair and free ClO4- anion in the concentrated solutions.     

FT-IR and FT-Raman vibrational spectra and molecular structure investigation of nicotinamide: A combined experimental and theoretical study

In this work, the experimental and theoretical spectra of nicotinamide (C₆H₆N₂O) are studied. FT-IR and FT-Raman spectra of title molecule in the liquid phase have been recorded in the region 4000–100 cm^?1. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree–Fock and density functional method (B3LYP) with the 6-31+G*(d, p) and 6-31++G* (d, p)basis set. The vibrational frequencies have been calculated and scaled values have been compared with the experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found in good agreement. The DFT-B3LYP/6-31++G (d, p) calculations have been found are more reliable than the ab initio HF/6-31+G (d, p) calculations for the vibrational study of nicotinamide. The optimized geometric parameters (bond lengths and bond angles) are compared with experimental values of the molecule. The alteration of vibrational bands due to the substitutions in the base molecule is also investigated from their characteristic region of linked spectrum.     

In vivo participation of artificial porphyrins in electron-transport chains: electrochemical and spectroscopic analyses of microbial metabolism

The effects of artificial porphyrins on the electron-transport chains of living microbes were investigated. The participation of porphyrins in the microbial electron-transport chains was demonstrated by spectroscopic and current-generation measurements. Large enhancement of the microbial current generation was accomplished by adding a cationic water-soluble manganese porphyrin as an electron mediator.     

Nitro-functionalized oligothiophenes as a novel type of electroactive molecular material: spectroscopic,electrochemical, and computational study

A novel series of terthiophenes bearing electron-donor and electron-acceptor groups at the end alpha-positions has been prepared. The analysis of the UV-vis, infrared, and Raman spectra, performed with the aid of density functional theory calculations, shows that the asymmetrically substituted nitro compounds PhT(3)NO(2) and BrT(3)NO(2) behave as push-pull systems and present an intense photoinduced charge transfer in the visible spectrum. The symmetrically substituted dinitro compound NO(2)T(3)NO(2) displays a highly delocalized structure with a low single-double bond length alternation and also displays a low-energy absorption band in the visible region. The novel nitroterthiophenes possess attractive electrochemical properties since they generate stable species both upon oxidation and reduction. Oxidation mainly involves changes in the oligothiophene backbone and leads to the formation of stable cations even for NO(2)T(3)NO(2). Reduction is mainly nitro-centered but also affects the conjugated structure. Radical anions and dianions are formed for PhT(3)NO(2) and BrT(3)NO(2). Dianions, not radical anions, and trianions are obtained for NO(2)T(3)NO(2). Nitro-functionalized terthiophenes are shown to be very promising as electroactive molecular materials since they behave as push-pull systems, present a very intense photoinduced charge transfer in the visible region, and could act as both n- and p-channel conductors in organic electronic transistors.     

Ultrasound measurements of skin thickness after UV exposure: a feasibility study

High-frequency ultrasound images were used to measure the thickness of the dermis and epidermis of four human subjects. These measurements were performed before and after a single exposure to ultraviolet radiation (UV). Doses ranging from 0.5 to 3 minimal erythema doses (MED) were delivered to the skin of the back of four human subjects, and thickness measurements were made over a period of 16 days. We found: (1) exposures > or = 2 MED caused a 10-30% increase in the thickness of the dermis-epidermis layer; (2) the thickening response was not always in direct proportion to the UV dose; (3) maximum thickening response time was 48 h for the 2.8-3.0 MED exposure levels; (4) "diffusion" or spreading of the thickening response to neighboring areas occurred in some cases, as far as 4 cm from the exposed region (center-to-center), with changes ranging from 12% to 17%; (5) decreased thickness of the dermis-epidermis layer of up to 12% was observed for 3 out of 4 of the subjects.