Protonation beams

X-radiation can also be induced by high energy (several Me proton beams from ion accelerators. Such particle-induced x-ray emission (PIXE) (284) is useful for thin samples and particulates, having detection Hmits of g. Intense synchrotron x-ray sources have found appHcations in... 

These reactions may be used, respectively, to profile and N, using incident proton beams, or to profile hydrogen, using incident beams of and N. 

Straggling effects become more dominant further into the sample. They are most pronounced with proton beams, because the ratio of energy straggling to energy loss decreases with increasing ion mass. For protons, these effects may be quite substantial for example, depth resolutions in excess of 1000 A are typical for 1-MeV protons a few pm into a material. 

High Pressure Mass Spectrometry with a m.e.v. Proton Beam... 

Principles and Characteristics Particle-induced X-ray emission spectrometry (PIXE) is a high-energy ion beam analysis technique, which is often considered as a complement to XRF. PIXE analysis is typically carried out with a proton beam (proton-induced X-ray emission) and requires nuclear physics facilities such as a Van der Graaff accelerator, or otherwise a small electrostatic particle accelerator. As the highest sensitivity is obtained at rather low proton energies (2-4 MeV), recently, small and relatively inexpensive tandem accelerators have been developed for PIXE applications, which are commercially available. Compact cyclotrons are also often used. 

Volatile specimens Necessitates bringing proton beam into air No problems... 

Applications The main application fields of PIXE are earth science, air pollution studies (aerosol analysis), mineralogical studies, forensic science, arts and archaeology. In the external-beam PIXE technique, the proton beam is taken out to ambient air. This mode finds application in the analysis of art objects (paintings, books, etc.). 

Si(Li) spectroscopy, with the capability of simultaneous quantitative analysis of 72 elements ranging from sodium through to uranium in solid, liquid, thin film and aerosol filter samples. The penetrating power of protons allows sampling of depths of several tens of microns, and the beam itself may be focussed, rastered or varied in energy. The use of a proton beam as an excitation source offers several advantages over other X-ray techniques, for example there is a higher rate of data accumulation across the entire spectrum which allows for faster analysis. 

Johansson et al. (1995) illustrate the detection limits for the above type of specimens in terms of concentrations (ppm). Contours are shown in Figure 4.18 showing the dependence of the detection limit upon the trace element atomic number (Z) and the proton beam energy Ep. 

Faiz et al. (1996) have applied micro-PIXE analysis to study solute distributions in a single crystal sample of YiBa2Cu307 5 high temperature superconductor (YBCO) of dimensions 1.3 mm x 1.5 mm x 75 pm. It contained a small secondary crystal overgrowth of dimensions 340 x 340 x 100 pm3. The interface region between the smaller crystal and the base crystal was covered with a material which appeared to be residual flux. The instrument employed a 2.5 MeV focused proton beam of about 4 pm resolution, which could scan an area of 500 x 500 pm2 on the sample surface. The microbeam current was kept low (typically about 30 pA) to avoid any damage to the sample. 

Microbeam scanning of the sample cross-section was performed with an external microbeam (in air), using a focused 4 MeV proton beam and a 50 pm thick Kapton foil at the vacuum-air interface, with a 5 mm diameter beam exit hole. The 2 mm thick slice of gel polymer sample was placed less than 100 pm from the exit foil, with the cross-section facing the Kapton foil. A HPGe y-ray detector was placed just behind the sample in order to achieve as large as possible detector solid angle. The ion current was kept below 100 pA in order to minimize damage to the sample. 

The PIXE microbeam technique has a spot size in the range 1-10 pm, and this enables a study of the spatial distribution of elemental concentrations. The advantage of p-PIXE over EPMA is a very much increased analytical sensitivity due to the much lower Bremsstrahlung background generated by the proton beam. The detection limits are of the order 0.1% for EPMA and 0.001% using the p-PIXE technique. 

MeV required in proton-therapy for an effective treatment of deep seated tumors [26]. Fuchs and co-authors have proposed a scaling law [27], allowing the necessary laser parameters to produce proton beams of interest for such applications to be estimated. In their work, best suited to hundreds of fs/some ps duration laser pulses, they use the self-similar fluid model proposed by Mora [28] giving the following estimate for the maximum FWD proton energy ... 

The proton beam laminarity has been checked by imaging a 12.7 pm step grid placed parallel to the target onto RCF (Fig. 10.8). Using the line-outs of the grid on the RCF [69] and the profiles from the Thomson Parabola [70], we estimated an emittance of 0.067T mm mrad for the FWD beam and 0.127T mm mrad for the BWD. 

Fig. 10.8. Shadow of grid meshes (periods 500 and 12.7 pm) made on radio-chromic film by the 0.45 MeV component of the BWD (left) and FWD (right) proton beam. In both images, the small step grid is clearly visible...

Three analytical techniques which differ in how the primary vacancies are created share the use of such X-rays to identify the elements present. In X-ray fluorescence, the solid sample is irradiated by an X-ray beam (called the primary beam), which interacts with the atoms in the solid to create inner shell vacancies, which then de-excite via the emission of secondary or fluorescent X-rays - hence the name of the technique. The second uses a beam of electrons to create the initial vacancies, giving rise to the family of techniques known collectively as electron microscopy. The third and most recently developed instrumentation uses (usually) a proton beam to cause the initial vacancies, and is known as particle- (or proton-) induced X-ray emission (PIXE). 

This chapter discusses the range of analytical methods which use the properties of X-rays to identify composition. The methods fall into two distinct groups those which study X-rays produced by the atoms to chemically identify the elements present, and X-ray diffraction (XRD), which uses X-rays of known wavelengths to determine the spacing in crystalline structures and therefore identify chemical compounds. The first group includes a variety of methods to identify the elements present, all of which examine the X-rays produced when vacancies in the inner electron shells are filled. These methods vary in how the primary vacancies in the inner electron shell are created. X-ray fluorescence (XRF) uses an X-ray beam to create inner shell vacancies analytical electron microscopy uses electrons, and particle (or proton) induced X-ray emission (PIXE) uses a proton beam. More detailed information on the techniques described here can be found in Ewing (1985, 1997) and Fifield and Kealey (2000). 

This comprises mainly neutrons and gamma rays, and large ionized particles (fission products) close to the fuel elements. The neutrons largely produce protons in hydrocarbon polymers by "knock-on" reactions, so that the radiation chemistry of neutrons is similar to that of proton beams, which may alternatively be produced using positive-ion accelerators. 

Effect of Proton Beam Energy on the Sensitivity and Contrast of Select Si-Containing Resists... 

Table IV. The proton beam sensitivity of PMOTSS and its copolymers...

Figure 4. The effect of proton beam energy on the sensitivity (QH) of the MOTSS copolymer resists.

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