Low Z Elements of High Grade Metamorphic Rocks by PIXE Analysis-1 A Comprehensive Review 2

11 The majority of PIXE analytical study on geosciences has used 3 MeV proton beams for excitation and these 12 studies generally uses the K-X-rays for low Z elements and L-X-rays for high Z elements. The present study of 13 resulting spectra of metamorphic high grade rocks like charnockite can require striping techniques to resolve 14 interference problems between low and high Z elements on the applications of light energy-PIXE using Si (Li) 15 detector. In all forms of X-ray analysis, including thick-target light energy-PIXE, the X-ray signal is a dependent of 16 the ionization cross section and for low-energy protons, the cross section is high for the K shells of light elements 17 and the L shells of heavy elements in charnockite rock providing sufficient fluorescent yield for analytical purposes. 18 For Z > 55, 3 MeV protons cannot ionize K-shell electrons and analysis depends on the use of L-X-ray lines in 19 charnockite rock. Such L-X-ray spectra are complicated and can be affected by interferences K-X-rays from low Z 20 elements. The low Z elements present in the charnockite were identified by previous complementary analytical 21 techniques, but not identified in this study due to the above PIXE experiment limitations, and also particularly due to 22 the dimensions of Si (Li) detector because of low energy K-X-rays of the elements absorbed by the detector 23 window. Both interferences complexity and detector efficiency can lead to difficulties and ambiguity in the 24 interpretation of spectra of low Z charnockite composition, a problem that is exacerbated by uncertainty in relative 25 K-X-ray line intensities of low Z elements. From this investigation, the light energy-PIXE is ideal for the analysis of 26 low Z<55 elements except lower K-X-rays of Z<17 elements using K-X-ray lines without high Z elements present 27 in charnockite samples. 28 Keywords;Metamorphic high grade rock, Thick-target LE-PIXE, Low Z elements, Complexity, Spectral overlap, 29 Detector efficiency, Review. 30


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It has already been shown that the mineralogy and petrography of the charnockitie gneiss in the study area are 32 similar to that of metamorphosed igneous rocks with a basic affinity. Presence of characteristic minerals like 33 almandine garnet, pyroxenes indicates that the charnockitie gneiss is a high grade metamorphic rock. , In this section 34 it is proposed to study its major and. trace element chemistry with an object of understanding more about its genesis.

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H. Moseley experimented out the characteristic X-rays induced when materials were bombarded with cathode 59 rays. Since electrons are particles too, this is the first report of Particle Induced X-ray Emission. In the first 60 described the spectrometer and pointed out that his elemental samples were contaminated with impurities saying 61 presciently. The prevalence of X-ray lines due to impurities suggests that this may prove a powerful chemical 62 analysis. In his second, he systematically measured K and L line wavelengths or energies. But Charles Barkla is 63 responsible for the first recognition of characteristic X-ray lines of elements, it was in his paper that he first named 64 X-ray "fluorescence", and introduced the "K" and "L" notation: mid alphabet letters being used since both longer 65 and shorter wave-lengths were expected. The first report of modern PIXE using Si (Li) detectors was by Johansson 66 and others who suggested that trace-element detection limits could be as low as ng/g, and analysed geological 67 materials.

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Among various elemental analytic tools (Olabanji, et. al., 1996, Felix, et. al., 2017) PIXE is the most 69 significant which are based on the use of the material to be quantified as a target for a beam of accelerated particles.

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The determination of the characteristic energy emitted by the incident beam is then used to identify and quantify the 71 presence of the various elements in the material. In PIXE (Christopher, et. al., 2016) what are exploited are, in 72 particular, the X-rays emitted from the target material, whose energies are characteristic of the emitting atomic 73 species. A technical description then follows of how proper beams for PIXE are produced and of the experimental 74 setups commonly used. The X-ray detector characteristics, the electronics for constructing the energy spectra, and 75 the software processes for their deconvolution, leading to the extraction of quantitative data, are then briefly 76 described in case of analysis of low Z elements of Charnockite composition.

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Moseley employed good resolution technique, wavelength dispersive spectroscopy which is a quite suitable of 78 detection differences in the atomic electron structure due to different bonding states. This valence information is 79 routinely used in the electron spectroscopy and absorption spectroscopy. It can also be used in PIXE, if a high 80 resolution detector is used which could be WDX or one of high resolution calorimetric EDS detectors. Of course 81 high resolution also allows disentangling of overlapping peaks which often accuse, especially for the L lines and is 82 one main reason of the degradation of sensitivity. Three physical effects have to be quantified to use PIXE for 83 analysis. 1) Ionisation cross-section 2) Fluorescence probability and 3) Mass absorption; these are all quite 84 complex and need describing separately. To this needs to be added the energy loss of the incident particles in the 85 sample, which is of course exactly the same as for the particle reaction technique. We should note here that PIXE atomic excitation methods.

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Among all the previous analytical methods, PIXE technique has its own merits and demerits (Javier, 2016) over 89 the other techniques. Using the analysis of the present study, it could be concluded the level of working of PIXE 90 (Satyanarayana, et. al., 2019) at low Z elements with respect to previous analytical tools of same location of the 91 charnockite samples by comparisons. An attempt also made to present the genetic aspect of the charnockites studied 92 by obtaining geo chemical data through review of the PIXE spectrum compare with previous analytical methods.

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The aim of the present investigation is calculating the quantification values of all elements and also review in matrix 94 Precambrian samples of low Z elements in charnockite samples of hill near Visakhapatnam airport using particle 95 induced X-ray emission technique with 3 MeV.   direction is placed at an angle of 90 0 with respect to the beam direction also placed in the chamber at an angle of 110 135 0 with respect to the beam direction. The Si (Li) X-ray detection output is connected to system of data 111 acquisition which gathers the X-ray spectrum. The spectrum of each sample is noted for a sufficiently enough time 112 so as to achieve valuable statistics.

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The Guelph PIXE (GUPIX) (Maxwell, et. al., 1995) software package is employed to analyze the spectrums 114 utilizing a standard Marquardt non-linear least square fitting procedure. This software package advantages is to 115 identify different elemental quantifications present in the target material and to calculate their relative intensities.

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Using this GUPIX software package the X-ray intensities of different elements are changed into the respective

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In the previous analytical results, the low Z elements in charnockite composition are started from analysis Li 196 and Be, but these are not detected in this present PIXE at 3MeV spectrum because of low energy K X-rays induced 197 from low Z elements in charnockite, and these are absorbed by detector window of the Si (Li) detection and in

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The smooth Si (Li) detection volume ranges from order of 10 mm diameter, and order of 5 inch thickness is resistant to environmental degradation. With these windows low Z elements like carbon (0.282 keV K X-rays) has 210 been measured (Szegedi, et. al., 1996).

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The element Li have no X-ray and Be with X-ray energy Kα= 0.108 keV are not detected even though these

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From this investigation of charnockite matrix composition, the idea of production cross sections of X-ray for 230 low Z elements is required for quantitative analysis by PIXE method. This is a simplest and basic widely accepted

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It is required to convert calculating X-ray production cross-section to ionization cross-sections using L-sub shell 243 fluorescence and Coster-Kronig yield.

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For protons with low energy, the cross section is high for the K shells of low Z elements and the L shells of 245 high Z elements, providing sufficient fluorescent yield for analytical purposes. For heavy elements (Z > 55), protons 246 with low energy cannot ionize K-shell electrons (Hajivaliei, et. al., 1993) and analysis depends on the use of L X-ray 247 lines from the above results. Such L X-ray spectra (Z > 55) are complicated and can be affected by interferences K 248 X-rays from lighter elements greater than Z=20 in the above results of chanockite samples. Both spectral 249 interferences (Pantelica, et. al., 2011) and complexity can lead to problematic and ambiguity in the interpretation of 250 K-line spectra of low Z>20 elements, a problem that is exacerbated by uncertainty in relative L X-ray line intensities 251 of hiher Z elements. Also in thick-target light energy-PIXE, the proton beam is stopped by the sample, producing an 252 important background radiation from proton scattering and matrix effects; this can obscure X-ray signals from 253 elements present in low concentrations. Light energy-PIXE probes can provide in situ analysis with less spatial 254 resolution, and lower limits of detection than that obtained by previous charnockite electron probe microanalysis.

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From the above results discussion of charnockite samples, light energy-PIXE is ideal for the analysis of trace 256 elements (Z < 55) except above Z<17 using K X-ray lines of elements present in the above charnockite samples.

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The K lines are used for elements 17 < Z < 55 in the above charnockite, and L X-ray lines are used for Z >55.

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From the investigation of PIXE, low Z elements detection is possible through K-X-rays. But these K-X-rays at 292 low Z elements have less energetic which are lies in between 0 to 2 keV and detection is not possible in the above 293 study though the Si (Li) detectors. Si (Li) detector with low diameter detection provide better energy resolution of 294 elements at low characteristic X-ray energies, and the thicker detectors have better detection efficiency at energies of 295 the X-rays above about 20 keV. The X-ray enters the cryostat through a thin beryllium window to reach the detector.

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The Be windows of detectors are typically 8-25.4 pm thick. The thickness of the window sets the lower energy limit 297 for photons that can be detected by the detector.

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The limitation of PIXE at 3 MeV is that below or near the Cl from spectrums of PIXE are not detected at all in 299 this work due to low energy X-rays from low Z elements, because they are absorbed in either the detector window, 300 atmosphere or through any filter used. Therefore the elements Li, Be, F, Na, Mg, Al, Si and P present in

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Charnockites are not detected due to the above explanation.

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In case of PIXE analysis, maximum number of the elements present in charnockites, interference is encountered 303 between the Kα of next element X-ray and the Kβ of previous element X-ray, which have virtually the near or same 304 energy and also between the X-ray K lines of media elements and X-ray L lines of heavy elements. PIXE 305 experimental work on minerals has used 3 MeV proton beams for excitation and low-energy normally uses the K-X 306 rays for low Z and L X-rays for high Z analysis. The present resulting spectra of charnockite rock can require 307 striping techniques to resolve overlap problems between light and heavy elements on the applications of light 308 energy-PIXE using Si (Li) detector.

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Si (Li) detection with AP.3 ultra-thin polymer window (SGX Sensortech) with active surface area 30 mm2 was 310 employed to detect low and medium Z elements energy X-rays (0.2-12 keV, Z > 5). A detector is protected by 311 permanent magnet from the scattered protons. Si (Li) with Gresham type Be windowed X-ray detection with 30 mm2 active surface area equipped adding kapton filter of thickness 125 μm was employed to detect the medium and 313 high Z energy X-rays (3-30 keV, Z < 19).

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Both complexity due to the interferences and detector efficiency can lead to problematic and ambiguity in the 315 conclusion of spectra, a problem that is exacerbated by uncertainty in relative K X-ray line intensities of low Z 316 elements. From this experimental investigation, the LE-PIXE is suitable for the analysis of low Z < 55 elements 317 except very low Z elements (Z<17) only using K X-ray lines without high Z elements present in geological samples.

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PIXE is very well suited for the analysis of geological samples except few conditions like above and for low Z 319 element analysis, hence the complementary technique of particle-induced γ-ray emission or NRA is required at 320 complex matrix composition-low Z elements.