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Dear Gaters,
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<div class="">thanks to a hint from my colleague Stefan van der Sar the issue got solved. I took the values from the NIST database values for the mixture instead of compound, while using the formula of the compound. Equivalently, the Gate database fractions
have to be given in fractions of weights.</div>
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<div class="">I’m sorry for any confusion I might have caused.</div>
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<div class="">Kind regards,</div>
<div class="">David</div>
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<div class="">On 8 Mar2021, at 17:05, David Leibold <<a href="mailto:D.Leibold@tudelft.nl" class="">D.Leibold@tudelft.nl</a>> wrote:</div>
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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=""><span id="cid:3F136832-F645-468E-A35A-119B27288818"><attachment.png></span></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=""><span id="cid:DC607FE3-CC31-4736-8D8F-6D68DAD45607"><attachment.png></span></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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