Nuclear microscopy

LAMMA has been utilized for the analysis of aluminum in brain tissue affected with Alzheimer s disease (Lovell et al. 1993). This new analytical technique of nuclear microscopy can simultaneously image and analyze features in unstained and untreated tissue sections, and therefore avoids contamination problems associated with tissue prepared using conventional chemical techniques. LAMMA was used in a study... 

Grime, G.W. (1998) Analysis of individual environmental particles using microPIXE and nuclear microscopy. X-Ray Spectr., 27, 221. 

Microprobe techniques, and their detection limits (given in mgkg ), that have been applied to Al localization include energy dispersive (electron probe) X-ray microanalysis (20), wavelength-dispersive X-ray microanalysis, electron energy loss spectrometry (500), proton probe nuclear microscopy (10), resonance ionization mass spectrometry (3), secondary ion mass spectrometry (1), laser microprobe mass spectrometry (1) and micropartide-induced X-ray emission (Yokel 2000). 

Sample preparation Sample preparation for nuclear microscopy is similar to that required for electron microscopy with the benefit that because of the much longer range of protons in matter (typically 30-100 )tm), there is no requirement for ultrathin samples, and in many cases samples can be analysed with little or no sample preparation. Table 2 summarizes the main types of sample preparation that may be required for nuclear microscopy. 

The lateral resolution of 0.5 allows experiments at the subcellular level. Initial work has concentrated on the localization of elements In specific sites of the tissue. Typical examples involve the assessment of aluminium levels in the bones of chronic haemodialysis patients, the study of lead accumulation in kidneys and calcifications in intraperitoneal soft tissue as a result of chronic lead intoxication, and the detection of several heavy metals in the amalgam tattoos of the oral mucose membrane and human gingiva in direct contact with dental alloys. The relatively low lateral resolution, the lack of automated mapping and the almost impossible quantization strongly hinder the use of LMMS, especially in view of analytical electron microscopy (AEM) with X-ray analysis and the emerging possibilities of nuclear microscopy. 

These two references give an excellent overview over the most recent examples in this research field. Callaghan P T 1993 Principles of Nuclear Magnetic Resonance Microscopy (Oxford Clarendon)... 

For bulk structural detemiination (see chapter B 1.9). the main teclmique used has been x-ray diffraction (XRD). Several other teclmiques are also available for more specialized applications, including electron diffraction (ED) for thin film structures and gas-phase molecules neutron diffraction (ND) and nuclear magnetic resonance (NMR) for magnetic studies (see chapter B1.12 and chapter B1.13) x-ray absorption fine structure (XAFS) for local structures in small or unstable samples and other spectroscopies to examine local structures in molecules. Electron microscopy also plays an important role, primarily tlirough unaging (see chapter B1.17). 

A variety of experimental techniques have been employed to research the material of this chapter, many of which we shall not even mention. For example, pressure as well as temperature has been used as an experimental variable to study volume effects. Dielectric constants, indices of refraction, and nuclear magnetic resonsance (NMR) spectra are used, as well as mechanical relaxations, to monitor the onset of the glassy state. X-ray, electron, and neutron diffraction are used to elucidate structure along with electron microscopy. It would take us too far afield to trace all these different techniques and the results obtained from each, so we restrict ourselves to discussing only a few types of experimental data. Our failure to mention all sources of data does not imply that these other techniques have not been employed to good advantage in the study of the topics contained herein. 

Radiation Damage. It has been known for many years that bombardment of a crystal with energetic (keV to MeV) heavy ions produces regions of lattice disorder. An implanted ion entering a soHd with an initial kinetic energy of 100 keV comes to rest in the time scale of about 10 due to both electronic and nuclear coUisions. As an ion slows down and comes to rest in a crystal, it makes a number of coUisions with the lattice atoms. In these coUisions, sufficient energy may be transferred from the ion to displace an atom from its lattice site. Lattice atoms which are displaced by an incident ion are caUed primary knock-on atoms (PKA). A PKA can in turn displace other atoms, secondary knock-ons, etc. This process creates a cascade of atomic coUisions and is coUectively referred to as the coUision, or displacement, cascade. The disorder can be directiy observed by techniques sensitive to lattice stmcture, such as electron-transmission microscopy, MeV-particle channeling, and electron diffraction. 

A detailed account is given in Reference 20. The techniques giving the most detailed 3-D stmctural information are x-ray and neutron diffraction, electron diffraction and microscopy (qv), and nuclear magnetic resonance spectroscopy (nmr) (see Analytical methods Magnetic spin resonance X-ray technology). 

Although experimental studies of DNA and RNA structure have revealed the significant structural diversity of oligonucleotides, there are limitations to these approaches. X-ray crystallographic structures are limited to relatively small DNA duplexes, and the crystal lattice can impact the three-dimensional conformation [4]. NMR-based structural studies allow for the determination of structures in solution however, the limited amount of nuclear overhauser effect (NOE) data between nonadjacent stacked basepairs makes the determination of the overall structure of DNA difficult [5]. In addition, nanotechnology-based experiments, such as the use of optical tweezers and atomic force microscopy [6], have revealed that the forces required to distort DNA are relatively small, consistent with the structural heterogeneity observed in both DNA and RNA. 

The methods used to characterise polymers are partly familiar ones like X-ray diffraction, Raman spectroscopy and electron microscopy, partly less familiar but widespread ones like neutron scattering and nuclear magnetic resonance, and partly... 

A study on the effectiveness of the E-plastomers as impact modifiers for iPP was carried out in relation to the traditional modifier EPDM. In this study, the flow properties of the E-plastomer-iPP and EPDM-PP blends were also evaluated. The blends were analyzed by solid-state 13C-nuclear magnetic resonance (NMR) spectroscopy, microscopy (SEM), and DSC. The results showed that E-plastomer-PP and EPDM-PP blends present a similar crystallization behavior, which resulted in a similar mechanical performance of the blends. However, the E-plastomer-PP blend presents lower torque values than the EPDM-PP blend, which indicates a better processibility when E-plastomer is used as an impact modifier for iPP. 

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. 

P. T. Callaghan 1994, Principles of Nuclear Magnetic Resonance Microscopy, Clarendon Press, Oxford, 490 pp. Standard reference textbook for imaging, some examples but with a focus on theory. 

---