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Dear Gaters,
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<div class="">(Note: I’m using Gate on the vGate machine 9.0, including GATE version 9.0 and geant4-10-06-patch-02.)</div>
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<div class="">I checked the physics in Gate by simulating the attenuation of a monoenergetic beam through phantoms of different compositions. So far I have checked water, LuAP, LYSO, aluminium, silicon, calcium and iodine. For all materials (except LuAP), the
relative error to the NIST reference data is below 2 % in the energy range 10 – 150 keV. </div>
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<div class="">In the case of LuAP, the results were initially off by about a factor of about 2 (not a constant factor, though). </div>
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<div class="">This is the spectra I got:</div>
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<div class=""><img apple-inline="yes" id="E539CDD3-F670-4106-AB74-5FAE870AED03" class="" src="cid:3F136832-F645-468E-A35A-119B27288818"></div>
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<div class="">The graph labelled with "n=..." is obtained by defining LuAP in Gate’s material database with the following definition, using integer ratios:</div>
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<div class=""><font face="Consolas" class=""> LuAP: d=8.34 g/cm3; n=3 ; state=Solid</font></div>
<div class=""><font face="Consolas" class=""> +el: name=Lutetium ; n=1</font></div>
<div class=""><font face="Consolas" class=""> +el: name=Aluminium; n=1</font></div>
<div class=""><font face="Consolas" class=""> +el: name=Oxygen; n=3</font></div>
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<div class="">Please note that this is the definition as shipped with the Gate examples. </div>
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<div class="">The graph labelled with "f=..." is obtained by defining LuAP in Gate’s material database with the following definition, using float ratios of 1:</div>
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<div class=""><font face="Consolas" class=""> LuAP: d=8.34 g/cm3; n=3 ; state=Solid</font></div>
<div class=""><font face="Consolas" class=""> +el: name=Lutetium ; f=0.2</font></div>
<div class=""><font face="Consolas" class=""> +el: name=Aluminium; f=0.2</font></div>
<div class=""><font face="Consolas" class=""> +el: name=Oxygen; f=0.6</font></div>
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<div class="">The graph labelled "NIST" denotes the attenuation coefficient data as obtained via NIST, which perfectly aligns with the graph labelled “f=…”, i.e. defining the material as fractions of 1.</div>
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<div class="">Except for how the LuAP material was defined in the Gate database, the Gate scripts and the evaluation code are the same.</div>
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<div class="">As a sanity check and to see what material composition Gate is using, I decided to fit the individual attenuation coefficients for lutetium, aluminum and oxygen as obtained by NIST to the output data "n=...", i.e. the data that is off. Here's
the fit result:</div>
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<div class=""><img apple-inline="yes" id="027EBC09-4571-40CE-B2CF-C5398EB0A902" class="" style="-webkit-user-select: none; display: block; margin: auto; padding: env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) env(safe-area-inset-left);" src="cid:DC607FE3-CC31-4736-8D8F-6D68DAD45607"></div>
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<div class="">The fit coefficients are as follows:</div>
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<div class=""><font face="Consolas" class=""> 0.69914713*NISTdata_Lu + </font></div>
<div class=""><font face="Consolas" class=""> 0.13694515*NISTdata_Al + </font></div>
<div class=""><font face="Consolas" class=""> 0.1097257 *NISTdata_O</font></div>
<div class=""><font face="Consolas" class=""> </font></div>
<div class="">As can be seen, the composition as used by Gate has little in common with the composition as defined in the database…</div>
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<div class="">So is this a bug or am I doing something wrong?</div>
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<div class="">Thanks in advance for your help!</div>
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<div class="">Kind regards,</div>
<div class="">David Leibold</div>
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