<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1256"><base href="x-msg://111/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div apple-content-edited="true"><div style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Hi Chris, </div><div><br></div><div>I know there are (or used to be) discrepancies in beta (plus or minus) spectra for the built-in radionuclides sources (due to the fact that these sources were created for imaging purpose) but not sure it would impact your results. </div><div><br></div><div>However, have a look at this paper, especially section II.A.1. </div><div><br></div><div>The paper mentions an underestimation of photon abundance with energies higher than 500 keV by MC code, as compared to measurements. </div><div>Since we're talking about normalized data, you can also see it as an overestimation of photon abundance for energies lower than 500 keV. I actually happen to have the data in my lab and I noticed a difference of a factor up to 2 for photons around 100-200 keV. </div><div><br></div><div>As far I as know, it is currently recommended to use the measured spectrum. </div><div><br></div><div>Hope this helps. </div><div><br></div><div>Thibault</div><div> </div><div><br></div></div><br class="Apple-interchange-newline"> </div> <br><div apple-content-edited="true"> <div style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>Post-doctoral fellow</div><div>Division of Medical Imaging Physics </div><div>Johns Hopkins Medical Institutions</div><div>JHOC 4260, 601 N. Caroline street, Baltimore, MD, 21287</div><div>Tel: +1 410 502 3772</div><div>Fax: +1 410 614 1060</div><div><a href="http://www.hopkinsradiology.org/dmip/">http://www.hopkinsradiology.org/dmip/</a></div></div><div><br></div></div><br class="Apple-interchange-newline"></div></body></html>