Problem 2577

Created attachment 838 [details]
input macro for rdecay01 simulation of 11B[9.876MeV] decay

While investigating a problem on the Geant4 forum ("Beta decay of 11Be" started 2023-11-22 in Physics Processes, Models and Cross Sections category), it was observed that in Geant4 simulation of the beta decay of 11Be at rest, a gamma ray of energy ~9.870 MeV was present. However, there does not appear to be any experimental evidence of the existence of such emission. Details of the problem are mentioned in the thread of the referenced forum post, but I will summarize below. 

The problem described was first noted for a program built on Geant4 10.7.4 (Operating System: Rocky linux 8, compiler: gcc version 8.5.0, cmake version: 3.20.2).  The output spectrum clearly shows a small gamma ray peak in a NaI(Tl) detector at 9.87 MeV. However, a review of published decay scheme data (e.g., Lederer and Shirley, Table of Isotopes, Seventh Edition Wiley 1978; TUNL Nuclear Data Project (https://nucldata.tunl.duke.edu/index.shtml) reveals that the 9.870 MeV level in 11B (formed after beta decay of 11Be) does not decay via direct or cascade gamma ray emission to the ground state of 11B. Its only available decay channel is via alpha decay to the first excited state or ground state of 7Li. Furthermore, a literature search, although not exhaustive, could not turn up any experimental evidence of the existence of a ~9.780 MeV gamma ray in such a decay. Thus from an experimental point of view, it seems that there should not be a 9.87 MeV gamma ray emission in the beta decay of 11Be.

The physics list used contains: G4EmLivermorePhysics(), G4DecayPhysics(), G4RadioactiveDecayPhysics(), G4OpticalPhysics().

The Geant4 problem was confirmed by running distribution example rdecay01 with its default physics list compiled on Geant4 11.01.03 (Operating System: Fedora Linux 39, compiler: gcc version 13.2.1, cmake version 3.27.7). The input macro file marina.mac.txt (attached) initiates the decay of 11B at an excitation energy of 9.876MeV. The output although not attached, shows many deexcitations from 9.876MeV to the ground state and gamma rays from 56 keV to 9.871 MeV.