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 ([math]4\pi[/math]) from [math]D_2O[/math] (90%[math]D_2[/math] concentration) in reaction [math]O16(\gamma,n)O15[/math] is presented below. Initially [math]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]O16(\gamma,n)O15[/math]. Figure in blue on the right is the neutron energy spectrum with energy cut applied.

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