D2O photodisintegration simulation

File:D2O photodis.pdf

File:Dustin anal.pdf

The result of GEANT4 simulation of neutron photoproduction on deuterium and oxygen-16 is presented below:

Neutron yield ($4\pi$) from $D_2O$ (90%$D_2$ concentration) in reaction $O16(\gamma,n)O15$ is presented below. Initially $5\cdot 10^7$ 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 $O16(\gamma,n)O15$. Figure in blue on the right is the neutron energy spectrum with energy cut applied.

Neutron yield ($4\pi$) from $D_2O$ (90%$D_2$ concentration) in reaction $D_2(\gamma,n)p$ is presented below. Initially $5\cdot 10^7$ 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 $D_2(\gamma,n)p$. 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 $O16(\gamma,n)O15$ and $D_2(\gamma,n)p$ reactions at (0MeV)<E<=5MeV, then the ratio of unpolarized photons from $O16(\gamma,n)O15$ and polarized photons from $D_2(\gamma,n)p$ will be $855/15128=0.056$. In the same time we will loose $(16799-15128)/15128=11%$ of the "good" neutrons produced in $D_2(\gamma,n)p$ reaction.

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.