An overview of PIXEand its applicationHummakosarInternationalIslamic University Islamabad This article willdiscuss the brief introduction to the PIXE technique and its applications indifferent fields of life. PIXE method is frequently referred to asProton-induced X-ray emission, due to the fact that, in this technique, protonsare commonly chosen to induce X-ray emission. Around the world PIXE isregularly applied for numerous interdisciplinary problems: Environmentalstudies, investigation of materials, in biomedicine, archeometry and geology etc.The vast applications of Particle Induced X-ray Emission (PIXE) has led to a significantattesntion to the research. History Proton Induced X-ray Emission (PIXE) was first introduced as auniversal analytical technique by Johansson et al.
1 at the Lund institute oftechnology in the early 1970s .Many analytical techniques were used to traceelement analysis, in comparison with PIXE it was observed that their samplepreparation was generally complicated and takes a long time. The popularity andrange of the PIXE applications has continuously increased over the years.Currently, throughout the world several laboratories are using PIXE forelemental analysis in diverse fields as environmental studies, biologymedicine, materials sciences, earth sciences etc 2-4. Conferences on PIXE andits use in applications are been held after every third year since 1977. Introduction The ability ofnon-destructive methods to perform multielemental determinations has led to anextensive applications in different industrial and research laboratories. ProtonInduced X-ray Emission (PIXE) is one of the most precise and sensitive atomic andnuclear analytical technique 5-7. Particle Induced X-ray Emission (PIXE) isPIXE is a technique used for the elemental analysis.
The sample preparation ofPIXE are generally simple, making it a very less time consuming technique. TheProton-induced X-ray emission is the most popularly used technique in thecategory of ion beam analysis 8. The accuracy and sensitivity ofProton-induced X-ray emission is much better for analysis of both matrix andtrace elements in thick samples as compared with other ion beam techniques 1.IN comparison with electron beam induced x-ray spectroscopy PIXE gives a muchhigher signal to background. PIXE is 100 times more sensitive compared toenergy dispersive X-ray spectroscopy. Due to its non-destructive andmulti-element analytical capability Proton-induced X-ray emission has found wideapplicability in various research fields. The popularity and the greatpotential to meet the current demand of trace elements analysis with PIXE isincreasing day by day 9.Principle of PIXE Proton Induced X-rayEmission (PIXE) mainly consists of two main parts.
In the first partidentification of the atomic species in the target from the energies of thecharacteristics peaks in the X-ray emission spectrum is done, while in thesecond part the amount of the element present in the target from the intensityof its characteristic X-ray emission spectrum is determined. The knowledge ofthe ionization cross-sections, fluorescence yields and absorption coefficientsis normally required for this process. By exciting the target atoms induced byan energetic ion beam of protons or alpha particles X-rays can be produced asshown in figure 1 10.In the PIXE technique theelement is identified by the energy of the characteristic X-rays and elementalconcentration for specific element gives us information about the number ofemitted X-rays with characteristic energy peak 11.In PIXE thesamples are bombarded with high-energy protons accelerated in an accelerator.These high energy protons strike the target atoms and electrons from the innershell are ejected.
As a result, in the innermost shell a vacancy is created.When protons interact with matter it results in the production of an X-Rayspectrum by the de-excitation of the atoms in the sample. The de-excitations ofthe atoms can also occur due to the emission of an electron, called Augerelectron.
The electronic transition that take place may be accompanied by theemission of electromagnetic radiation in the form of x-ray spectrum of theexcited atom. This emission of electromagnetic radiation in the form of X-rayscharacteristic is consist of K,L,M lines which are produced by the electronictransitions to the K,L,M.. Shells of the target atom. By doing so elementalcomposition analysis can be achieved by determining the X-ray emissionsoriginating from the excited sample.
The nondestructive nature of this technique and high sensitivityfactor has made this technique as one of the most suited to study the traceelement content of air particulate, analysis of soil, sediments and plants. Figure 1. Thebasic principle of PIXE. Ref 10 Applications of PIXE The analyticalapplications of PIXE are countless. Due to its non-destructive nature of thetechnique, PIXE is currently applied to a wide range of material analysis indifferent research laboratories all around the globe. The following discussionwill outline the different group of applications and different aspects of PIXEthat are important for its application in various fields.
EnvironmentalStudies Environmentalpollution Studies were among the first applications to be successfullyperformed during the early years of PIXE development. Currently investigationof water pollution and air pollution is been done with the help of PIXE, withmore emphasis on the latter. The aerosol analysis is significantly importantfor the air-quality assessment in urban and industrial areas as its impact onthe health of all living organisms is important. Using PIXE for aerosolanalysis provides an important tool for the investigation of many atmospheric phenomena’ssuch as air transportation, visibility and climate. Currently widespread use ofaerosol investigations by PIXE has become apparent. Every element is potentially important inaerosol analysis, it can be because of their toxic nature or maybe because anyof such compounds bound in particles with the help of scattering of light can affectthe visibility, also the simultaneous detection of group elements can also be asign of pollution.
By performing the multielemental quantitative analysis PIXEcan be an important tool to offer an advantage in terms of cost and time. UsingPIXE with other IBA techniques can also extend the range of detectableelements. The information on the composition of different sizes of aerosols isimportant to obtain. The relevance of particles having different sizes is verydifferent, and the distribution of the particle size is also non homogenous.The impact on health is mainly connected to the penetration of the particlesinto the breathing apparatus, smaller particles are potentially more dangerousbecause they reach much deeper levels into the breathing apparatus.
Thevisibility problems created by aerosols, the dependence of their effect on sizeis more obvious to be connected with the scattering of light. The distributionof the size also gives us worthy information on the different sources ofpollution. In comparison with other techniques, the higher sensitivity of PIXEcan be exploited to the highest degree, with no other technique can providesuch a high time resolution and sensitive detection of many elementssimultaneously in a short amount of time 8. Biomedical applicationsIn the last decade, PIXE techniques found great success in solving thebiological and biomedical problems. The research on biomedical samples has alsoincreased in the last few years.
Though PIXE is still a new member of thefamily of spectrographic methods but interest in this technique is growing dayby day. Apart from environmental studies majority of the PIXE applications arefound in biology and medicine. The small amount of the material and the time ofanalysis are important requirements for biomedical investigations in order toobtain significant cooleration between the trace elements and biomedicalphenomena, which can be easily carried out with the help of PIXE. Another importantfeature of using PIXE in medical applications is the high spatial resolution,which helps in the possibility of mapping the trace-element distributions inthe tissues with a much higher definition. The intercellular distribution oftrace elements can be revealed by using a micro beam and sometimes there are noother technique then micro-PIXE .
A close interdisciplinary collaborationbetween the physicists and biologists in problems like planning, samplepreparation data collection processing is important to obtain good results inbiomedical PIXE applications. From the toxicological point of view, traceelements such as lead are of significant interest. In addition to that,investigation for a possible link between the trace element concentrations andvarious diseases are also been studied 8,10. In the past, the main focus ofbiomedical PIXE applications was the detection of trace quantities oftransition elements and heavier atoms in tissues, recently higher elements likepotassium and calcium are also of great interest. When dealing with the smalltissues samples, often the low concentration levels of these elements are amajor issue in analysis by using other techniques .This problem was solved byPIXE as the concentrations of these elements were well within reach of PIXE.
Bio-PIXEexperiments are generally performed on such samples which are collected fromthe living matter. Many investigations are performed on dermatological sampleslike nails or hairs in order to avoid ethical problems connected with acquiringof such samples from living organisms. Such samples also serves as biologicalindicators of a physiological or pathological state of the individual fromwhich these samples are taken. The use of body fluids in the samplingprocedures also implies minimum invasion. The high absolute sensitivity of PIXEis a good reason for selecting this technique while dealing with biopsies(living matter).
However, special care should be taken because of the very smallamount of sampled material involved in order to avoid contamination from thesurgical instruments 8. Industrial applications The industrial applications of anyaccelerator-based technique depends on the availability of instrumentation. Nonavailability of instruments clearly limits the growth of applications in anindustry. There are only few semiconductor industries that have in-houseparticle accelerators which might improve this situation. IBA techniques had asignificant impact in the field of economic geology, by supporting traceelement data with the help of a nuclear microprobe on mineral samples 12.Geogas prospecting is one of themost important industrial application of PIXE.
The concept of using Geogas inprospecting is based on the emissions of small amounts from deep undergrounddeposits to the earth surface 13. In this method small particles are firstcollected on thin foils and then are exposed for serval weeks, after this theyare analyzed using a millimeter ion beam. Composition of the material depositedthen can be revealed by PDCE. By a rather complex interpretation procedureutilizing geophysical principles the nature mineral deposits in deep ground canbe judge. This technique has great potential in the evaluation of rockconditions in order to investigate the suitability of sites for highlyradioactive waste storage.
Another industrial applicationwhich is slightly different from the one discussed earlier is the use offocused ion beams for characterization of the fibrous structure of newsprintpaper and to analyze the characteristics of printing 14. PIXEand its scope in Pakistan Around the world PIXE is regularlyapplied for numerous research related problems. In the field of sciences andtechnology Pakistan is one of the most fastly developing country, IBAtechniques are popularly used around the world, PIXE being the most populariron beam analysis technique has vast applications in many fields of life. InAtomic and Laser Physics laboratory in National Centre of Physics Pakistan,tandem particle accelerator facilities are available. Proton-Induced X-RayEmission (PIXE) is one of the important techniques for the analysis ofmaterials which is offered in Atomic and Laser Physics laboratory in NationalCentre of Physics Pakistan.It has sensitivity up to 1 ppm and accuracy of 1%.
Currently there are severalprojects running in National Centre of Physics Pakistan for the purpose of Environmental science research.These projects include the indoor/outdoor air pollution study with the use ofPIXE/PIGE techniques. GC University Lahore has also 4MeV pelletron acceleratorwhich have two active beam lines. One of these beam line is being effectivelyused by different science departments of the University for the Proton-InducedX-Ray Emission (PIXE) analysis of materials. In Pakistan several researchscientist has used PIXE for different environmental, biomedical any many otherapplications.
Some of them are discussed in this article. Nisar Ahmad et al 15 did research on the aerosol studies of urbanareas of Lahore by using the PIXE technology. The trace elements were analyzedby using PIXE technology. It was observed that the cleaner residential areashad lesser amount of concentration of trace elements of anthropogenic origin.International Scientific Spring Conference which was held in Islamabad,Pakistan in march 2010, Nisar Ahmad also presented the analysis of some Medicalherbs by using the Proton-Induced X-Ray Emission (PIXE) technique .
Nisar Ahmad alsopresented his research work on the Proton-Induced X-Ray Emission (PIXE) technique in the 3rdInternationalConference on Frontiers of Advanced Engineering Materials which was organizedby PITMAEN, PCSIR, which was held at Lahore Pakistan. From the pastfew decades the chromium-based tanning industry has grown significantly inPakistan. However due to the rules and regulations imposed by Pakistanigovernment are not strictly followed for the effluent discharge from thetanneries. Tanner effluents has become a great source of water pollution. Lubnashakir et al 16 studied the characterization of tannery effluent waste waterby Proton-Induced X-Ray Emission (PIXE) analysis to investigate their role inwater pollution. This case study was done in Kasur Pakistan , wherecharacterization of tannery effluent wastewater (TW), shallow ground water(SW), and deep ground water (DW) were taken to determine that what are thesources of pollution in the district Kasur Pakistan. Results showed that the concentrationsof calcium (Ca), chlorine (Cl), chromium (Cr), iron (Fe), potassium (K), Mg,sulfur (S) silicon (Si) and Sr in Tw were much higher than SW and DW.
A.U.Rehman et al 17 studied the ElementalComposition of Groundnut with the help of Proton-Induced X-Ray Emission (PIXE),which highlighted the role of PIXE in elemental behavior in the field of agricultural research. Theresults showed by PIXE were a lot better than other techniques.Ali Shadet al 18 studied the standardization of proton-induced x-ray emissiontechnique for analysis of thick samples. For the standardization, threedifferent samples were taken of standard reference materials (SRMs) and thenthey were analyzed by using Proton-Induced X-Ray Emission (PIXE) technique.After this the final data was compared with the already known data of thesecertified SRMs. The final result showed that the data obtained by using PIXEtechnique was almost similar to the already known data of certified SRMs.
ConclusionPIXE is a multi-element non-destructive techniquewhich is known for its sensitivity, accuracy, precision, simplicity of targetpreparation which allows the detection of the presence of many elements in asample in a very short amount of time. PIXE has become a very popular techniquefor material analysis as it has vast applications in Environmental studies,investigation of materials, in biomedicine, archeometry and geology etc. It isone the best iron beam analysis technique. In a short spanof time PIXE has shown its versatility and usefulness by the diversity ofapplications it has. In future PIXE should find itself working in more usefulapplications with more variety of samples.
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