D2O photodisintegration simulation
Neutron spectra separation
The result of GEANT4 simulation of neutron photoproduction on deuterium and oxygen-16 is presented below:
Neutron yield ([math]\displaystyle{ 4\pi }[/math]) from [math]\displaystyle{ D_2O }[/math] (90%[math]\displaystyle{ D_2 }[/math] concentration) in reaction [math]\displaystyle{ O16(\gamma,n)O15 }[/math] is presented below. Initially [math]\displaystyle{ 5\cdot 10^7 }[/math] brem photons with 25 MeV end-point energy were thrown on the target. 410 neutrons initially produced got absorbed in the target (E=0MeV) and 2509 neutrons will likely escape the target. Figure in blue on the left is the total energy spectrum of neutrons created in reaction [math]\displaystyle{ O16(\gamma,n)O15 }[/math]. Figure in blue on the right is the neutron energy spectrum with energy cut applied.
Neutron yield ([math]\displaystyle{ 4\pi }[/math]) from [math]\displaystyle{ D_2O }[/math] (90%[math]\displaystyle{ D_2 }[/math] concentration) in reaction [math]\displaystyle{ D_2(\gamma,n)p }[/math] is presented below. Initially [math]\displaystyle{ 5\cdot 10^7 }[/math] brem photons with 25 MeV end-point energy were thrown on the target. 857 neutrons initially produced got absorbed in the target (E=0MeV) and 16799 neutrons will likely escape the target. Figure in black on the left is the total energy spectrum of neutrons created in reaction [math]\displaystyle{ D_2(\gamma,n)p }[/math]. Figure in blue on the right is the neutron energy spectrum with energy cut applied.
So, if we apply the energy cut in neutron spectrum which is a sum of neutrons coming from [math]\displaystyle{ O16(\gamma,n)O15 }[/math] and [math]\displaystyle{ D_2(\gamma,n)p }[/math] reactions at (0MeV)<E<=5MeV, then the ratio of "unpolarized" neutrons from [math]\displaystyle{ O16(\gamma,n)O15 }[/math] and "polarized" neutrons from [math]\displaystyle{ D_2(\gamma,n)p }[/math] will be [math]\displaystyle{ 855/15128=0.056 }[/math]. In the same time we will loose [math]\displaystyle{ (16799-15128)/15128=11% }[/math] of the "good" high energy neutrons produced in [math]\displaystyle{ D_2(\gamma,n)p }[/math] reaction. Binning is the same for all the plots.
I will verify if those spectra and all the ratios are the same in the case where we use the geometrical constrains applied by the detectors placement.