I’m interested in the decay of the first excited state of Zr-90. It is the source of the tiny positron branch in the decay of Y-90 and can be used for PET imaging. ENSDF only has the isomeric transition listed in the table for the isotope. Nickles et al (IEEE 2004) says that the 0+ -> 0+ nuclear level is constrained to decay by 2 gamma emission, internal conversion and internal e-/e+ decay. This is where the positron enters the picture. I’ve searched the G4 documentation and found that double beta decay is not modeled. I did note that there is e+/e- pair production modules with G4 EM physics lists but I think this production event is modeled from high energy gammas.
Anyone know if I’m correct about the assumptions I’ve made about these physics processes within G4/TOPAS? Anyone know a theoretical physicist that can help me with modeling this Zr-90 e-/e+ decay? I would like to get the kinematics as correct as I can since I want to study PET imaging of this reaction in detail. I thought to fake the events using F-18 as the e+ source and then adding a tabulated bremsstrahlung spectrum but I worry about spectrum differences between the F-18 and Zr-90 e+ decays that might be clinically relevant since the Zr-90 e+ is such a small signal.
I did find the BxDecay0 program by the BxCppDev group which is a C++ port of Vladmir Tretyak’s Fortran code. I’m trying to contact the authors about the code systems. Most of the theoretical work is on double beta decay with and without neutrinos and I would just like to help my old experimentalist mind wrap around it better.
Any help with this is greatly appreciated!
William A Dezarn, PhD
Wake Forest University School of Medicine
Winston-Salem NC USA