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<p class="MsoNormal"><span lang="EN-US">Yes, the process requires a significant neutron fluence but, suppose I change the proton beam to a neutron beam that is heavily weighted to lower energies. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><br>
</span></p>
<p class="MsoNormal"><span lang="EN-US">I aim the neutron beam on a Gadolinium based phantom. I still do not receive the prompt gamma rays and characteristic x-rays that should be represented from the interactions.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><br>
</span></p>
<p class="MsoNormal"><span lang="EN-US">Gadolinium has an enormous cross section for thermal neutrons approximately 48890 barns. Soft tissue is approximately 0.1 b.<o:p></o:p></span></p>
<p class="MsoNormal">The main spectral signature for Gd neutron capture reactions for X-rays at 43 keV (Gd K<span style="font-size:6.5pt;mso-bidi-font-size:11.0pt;
line-height:107%;mso-ascii-font-family:Calibri;mso-fareast-font-family:Calibri;
mso-hansi-font-family:Calibri;mso-bidi-font-family:Calibri">a</span>)
and 49 keV (Gd K<sub>b</sub>), and gamma-rays at 79.5 keV and 181.9 keV.<o:p></o:p></p>
<p class="MsoNormal"><br>
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<p class="MsoNormal">Either a proton beam or especially a neutron beam on Gadolinium should produce photons with these spectral energies.<o:p></o:p></p>
<p class="MsoNormal">I am using around 1 million particles incident on a Gd Phantom with a NaI detector.
<o:p></o:p></p>
<p class="MsoNormal"><br>
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<p class="MsoNormal">I have tried these physics builders: QGSP_BIC_HP, QGSP_BERT_HP, FTFP_BERT_HP. I have seen no capture reactions as a result.
<o:p></o:p></p>
<p class="MsoNormal"><br>
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<p class="MsoNormal"><b><i>I am starting to wonder if I do need an entire modified physics list.<o:p></o:p></i></b></p>
<p class="MsoNormal"><b><i>Also, the modified physics list might require very specific physics models for this to work.<o:p></o:p></i></b></p>
<p class="MsoNormal"><b><i>i.e. Protons -> Neutron Fluence -> thermal n + Gd Capture reaction -> gamma-rays + characteristic photons.</i></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am using the EnergySpectrumActor and can measure counts as a function of energy seen at the NaI detector. The only problem is that I am not seeing a representation of those neutron capture reaction energies measured at the detector. They
should be clearly defined. <o:p></o:p></p>
<p class="MsoNormal"><br>
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<p class="MsoNormal"><b><i>The primary problem is not seeing these capture reactions.
<o:p></o:p></i></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ll post an example of my macro, to provide greater insight.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As always, thank you for all the help, and all suggestions are greatly appreciated.<o:p></o:p></p>
<p class="MsoNormal">Thank you,<o:p></o:p></p>
<p class="MsoNormal">Kurt Van Delinder<o:p></o:p></p>
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