Nuclear probe techniques

Nuclei provide a large number of spectroscopic probes for the investigation of solid state reaction kinetics. At the same time these probes allow us to look into the atomic dynamics under in-situ conditions. However, the experimental and theoretical methods needed to obtain relevant results in chemical kinetics, and particularly in atomic dynamics, are rather laborious. Due to characteristic hyperfine interactions, nuclear spectroscopies can, in principle, identify atomic particles and furthermore distinguish between different SE s of the same chemical component on different lattice sites. In addition to the analytical aspect of these techniques, nuclear spectroscopy informs about the microscopic motion of the nuclear probes. In Table 16-2 the time windows for the different methods are outlined. 

Although the assumption that all apatite platelets are of equal thickness may not be well justified, it provides a useful approximation to the real situation. In fact, such assumption is inevitable for an ensemble technique like NMR. It is anticipated that HARDSHIP may be well suited to determine the relative thickness of apatite crystallites in different bone or dentin samples. We note in passing that C-REDOR, which is a hetero-nuclear recoupling technique with active suppression of homonuclear dipolar interaction,42 43 can be used to probe for the size of nanoparticles embedded in polymer matrix,44 provided that the nanoparticles do not... 

As discussed in Section II, the excited-state dynamics of polyatomic molecules is dictated by the coupled flow of both charge and energy within the molecule. As such, a probe technique that is sensitive to both nuclear (vibrational) and electronic configuration is required in order to elucidate the mechanisms of such processes. Photoelectron spectroscopy provides such a technique,... 

As demonstrated for CS2, the pump-and-probe technique with CMI is a promising tool for investigating how a nuclear wavepacket evolves in real time. Considering that few-cycle laser pulses are now becoming available, we are now entering into a new era when it will be possible to see molecules in intense laser fields in real time with highest temporal resolution [34,35]. 

Due to their high sensitivity, nuclear imaging techniques are well-suited to visualize targets present at low concentrations. PET and SPECT, with their picomo-lar sensitivity, allow for the imaging of most known targets using ligands that carry only one label each. As the radionuclide label is relatively small, the probes may even permeate into cells. However, the spatial resolution of nuclear techniques lies in the order of a few to tens of miUi-... 

Supramolecular chemical processes have afforded probes for multimodal imaging with MRl and nuclear techniques. X-ray CT is an anatomical imaging modality that is commonly used in conjunction with PET in order to overcome the resolution issues associated with nuclear imaging techniques. As a result, several combinations... 

Abstract In this tutorial we describe the basic principles of the ion implantation technique and we demonstrate that emission Mossbauer spectroscopy is an extremely powerful technique to investigate the atomic and electronic configuration around implanted atoms. The physics of dilute atoms in materials, the final lattice sites and their chemical state as well as diffusion phenomena can be studied. We focus on the latest developments of implantation Mossbauer spectroscopy, where three accelerator facilities, i.e., Hahn-Meitner Institute Berlin, ISOLDE-CERN and RIKEN, have intensively been used for materials research in in-beam and on-line Mossbauer experiments immediately after implantation of the nuclear probes. 

In Chap. 1 is written by Saburo Nasu, the reader will find a general introduction to Mossbauer Spectroscopy. What is the Mossbauer effect and What is the characteristic feature of Mossbauer spectroscopy These questions are answered briefly in this chapter. Mossbauer spectroscopy is based on recoilless emission and resonant absorption of gamma radiation by atomic nuclei. Since the electric and magnetic hyperfine interactions of Mossbauer probe atom in solids can be described from the Mossbauer spectra, the essence of experiments, the hyperfine interactions and the spectral line shape are discussed. A few typical examples are also given for laboratory experiments and new nuclear resonance techniques with synchrotron radiation. 

Pump-probe techniques using picosecond and sub-picosecond laser pulses have made it possible to probe chemical processes on the time scale of nuclear motions [22]. Figure 11.7A shows a typical measurement of the early time course of stimulated emission from a dye molecule (1R132) in solution [23]. The dye was excited on the blue side of its absorption band (830 nm) and stimulated emission was measured at 900 nm. The signal includes a slow rise component with a time constant of several hundred femtoseconds that represents part of the Stokes shift of... 

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

The spectroscopic techniques that have been most frequently used to investigate biomolecular dynamics are those that are commonly available in laboratories, such as nuclear magnetic resonance (NMR), fluorescence, and Mossbauer spectroscopy. In a later chapter the use of NMR, a powerful probe of local motions in macromolecules, is described. Here we examine scattering of X-ray and neutron radiation. Neutrons and X-rays share the property of being found in expensive sources not commonly available in the laboratory. Neutrons are produced by a nuclear reactor or spallation source. X-ray experiments are routinely performed using intense synclirotron radiation, although in favorable cases laboratory sources may also be used. 

In this chapter, three methods for measuring the frequencies of the vibrations of chemical bonds between atoms in solids are discussed. Two of them, Fourier Transform Infrared Spectroscopy, FTIR, and Raman Spectroscopy, use infrared (IR) radiation as the probe. The third, High-Resolution Electron Enetgy-Loss Spectroscopy, HREELS, uses electron impact. The fourth technique. Nuclear Magnetic Resonance, NMR, is physically unrelated to the other three, involving transitions between different spin states of the atomic nucleus instead of bond vibrational states, but is included here because it provides somewhat similar information on the local bonding arrangement around an atom. 

All the techniques discussed here involve the atomic nucleus. Three use neutrons, generated either in nuclear reactors or very high energy proton ajccelerators (spallation sources), as the probe beam. They are Neutron Diffraction, Neutron Reflectivity, NR, and Neutron Activation Analysis, NAA. The fourth. Nuclear Reaction Analysis, NRA, uses charged particles from an ion accelerator to produce nuclear reactions. The nature and energy of the resulting products identify the atoms present. Since NRA is performed in RBS apparatus, it could have been included in Chapter 9. We include it here instead because nuclear reactions are involved. 

It is particularly important to study process phenomena under dynamic (rather than static) conditions. Most current analytical techniques are designed to determine the initial and final states of a material or process. Instmments must be designed for the analysis of materials processing in real time, so that the cmcial chemical reactions in materials synthesis and processing can be monitored as they occur. Recent advances in nuclear magnetic resonance and laser probes indicate valuable lines of development for new techniques and comparable instmmentation for the study of interfaces, complex hquids, microstmctures, and hierarchical assemblies of materials. Instmmentation needs for the study of microstmctured materials are discussed in Chapter 9. 

The use of computer simulations to study internal motions and thermodynamic properties is receiving increased attention. One important use of the method is to provide a more fundamental understanding of the molecular information contained in various kinds of experiments on these complex systems. In the first part of this paper we review recent work in our laboratory concerned with the use of computer simulations for the interpretation of experimental probes of molecular structure and dynamics of proteins and nucleic acids. The interplay between computer simulations and three experimental techniques is emphasized (1) nuclear magnetic resonance relaxation spectroscopy, (2) refinement of macro-molecular x-ray structures, and (3) vibrational spectroscopy. The treatment of solvent effects in biopolymer simulations is a difficult problem. It is not possible to study systematically the effect of solvent conditions, e.g. added salt concentration, on biopolymer properties by means of simulations alone. In the last part of the paper we review a more analytical approach we have developed to study polyelectrolyte properties of solvated biopolymers. The results are compared with computer simulations. 

A number of techniques have been employed that are capable of giving information about amorphous phases. These include infrared spectroscopy, especially the use of the attenuated total reflection (ATR) or Fourier transform (FT) techniques. They also include electron probe microanalysis, scanning electron microscopy, and nuclear magnetic resonance (NMR) spectroscopy. Nor are wet chemical methods to be neglected for they, too, form part of the armoury of methods that have been used to elucidate the chemistry and microstructure of these materials. 

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