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UW-Madison GEOSCI 777 - Monte Carlo Exercise

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Geology 777 Monte Carlo Exercise 3: Win X-ray 9/24/09 Name ________________________Up to now we have been using Monte Carlo simulations mainly to examine the spatial extent of high energy electron scattering in materials. Some of the previous software also included simulations ofthe x-ray generation within a material and estimates of x-ray absorption within the sample (“matrix effect”), known as the phi rho Z curves. (Much more on that later in the course.)One of the students of Raynald Gauvin (CASINO originator), Hendrix Demers, created a windows simulation of X-ray spectra. The program is still in development and part of using the program is to identify ways to improve it—so if something doesn’t work, let me know! A program like this (and CASINO phi rho Z ability) is valuable not only for learning basic concepts but also in the real-world lab. Since these programs are based upon the physics of the processes (understood more-or-less pretty well)1 we can compare real life data with the simulated data, and troubleshoot faulty hardware – or faulty software. This week we will first go through some step-by-step instructions to learn about the features of Win X-ray, and then run some simulations that allow us to simulate some of the data we acquired in theEDS lab this week. You can download Win X-ray from the official site: montecarlomodeling.mcqill.ca (probably best to get it there as that should be the latest version, vs whatever I have sitting on the class web page.)The most recent version is 1.3.1 (as of 9/2009)1- Demonstration of Win X-Ray for simple case of Cu at 10 kVOpen the Win X-Ray programChose File ->NewNow in Option Simulation windowSet Incident Energy Start to 10 kVSet the number of electron trajectories to 1000Defaults ok: eg. Beam Diameter 10 nm.Set Beam Current to 2e-8 A (=20 nA)Check X-Ray Compute and Compute Characteristic, and Compute BackgroundChange TOA (take off angle) appropriate one for your SEM or EMP, e.g. here change to 40 and Theta (=90-TOA) X-ray to 50Click Next button Now in Option Specimen windowClick on Set Element for All Regions button for defining target composition, here only 1 elementNow in Option element for region 1 window:Change the atomic number Z to 29, or Symbol to Cu (Must capitalize 1st letter!)NOTE: Wt fraction total must =1, so if changing to multi-elements back to singleelement, make sure the weight fraction always is set correctly. Otherwise you cannot proceedClick Ok button (leave Option element for the region 1 window)Back to Option Specimen windowClick NextNow in Option X-ray window1 Though in some cases are/could be based upon empirical data, so similar samples should give good results regardless of how well the physics is understood.Page 1 of 4Set time in seconds to how long to run: start with 100 sec; Window should be 8 micron BeClick Next button Now in Advanced Option windowIgnore for now, click Next buttonNow in Physics Model windowIgnore for now, click Next buttonNow in Result General Option window: irrelevant for you here, but here is the meaning[Save result in File = Automatic (will automatically save all files in a folder in the Program folder); Manual means turn off because you want to manually write down the numbers]Click Next buttonNow in Result Trajectory Option windowCheck box to see a small number (e.g. 200) trajectories while the x-rays are being Click Next buttonNow in Result Distribution Option windowGenerally ok to accept the default values hereClick Finish … and it is running though nothing appears to be happening: look at the bottom barWait for the end of the simulation: bottom menu bar shows % progress, elapsed and remaining time. Last number (n) is the backscattered coefficient that is constantly being updated.Data now ready when the small “10 keV” indicator in the upper column is no longer greyed out.Click on + to expand the tree viewClick on the trajectory +Click on the interaction volume and adjust the new windows as you wishMove the mouse over the picture to find the max depth and radial dx (shown in bottom of image)Change the X-Z Plane to X-Y Plane by clicking the X-Z window immediately above, then X-YClick on BSETake some of the choices, see how much more freedom you have to read specific things, such asdistances, just by moving the cursor over the image, with readout on the bottom bar.Click on the X-Ray +Click on the PRZ Curves +, then particular element (Cu), then particular line (e.g.,Ka1, Lb1) Note that x-ray intensity vs depth (Z, on the horizontal axis), showing the generated (red) and emitted (green) distributions, easiest seen for the L lines.Click on Spectrum to show the complete spectrum with the effect of the detectorClick on the Y Axis LogCheck and uncheck Background, Characteristic, and TotalMove the mouse to read energy and intensity at the cursor.Without Y log scale checked, zoom on the K-Lines by left click + move down and right with the mouse to select the zoom region.To reset the view left-click + move up and left with the mouse.Now click Intensity: I Detect is the integrated Peak minus Background counts for each peak; Note the INTENSITY value for Cu Ka1._________ and Cu Ka2:_________ Add them together _________(call it “a”)Now click on “lines”, Cu, Ka1: here you see a modeled characteristic peak (yellow), continuum (green) and “total” P+B in red. Note that its center is not the same as the yellow peak. This is anintentional undocumented feature and the red peak is total in more than one sense of the word. Itis a weighed total of the Cu Ka1 and Ka2 peaks. Note the value for Total (red) Cu Ka1 _______ (call this “b”)--this is a much smaller number than “a” because it is the single channel number. Page 2 of 4One of the benefits of EDS over WDS is that the computer will integrate ALL the xrays in the peak curve – giving a higher number than just in the one single channel that is the theoretical peak position.The take home message here should be that (1) background needs to be subtracted (as when doing quantitative analysis) and (2) if you can integrate under the peak [easy in EDS!], you will have a lot more counts to improve your statistics (precision) and also (3) that Ka1 and Ka2 peaks are very close and in EDS you cannot distinguish. The reason he shows both Ka1 and Ka2 is that BOTH can be modeled in his Monte Carlo process. Why is there Ka1 and Ka2? Dig into the references (slide from 2nd class with “onion skin”


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UW-Madison GEOSCI 777 - Monte Carlo Exercise

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