# Coupled neutron-photon transport problem **URL:** \ **Category:** User Support\ **Created:** [January 15, 2021, 2:13am UTC](https://openmc.discourse.group/t/coupled-neutron-photon-transport-problem/942 "2021-01-15T02:13:43Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![MaryAAZ](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/maryaaz/32/1244_2.png) [@MaryAAZ](https://openmc.discourse.group/u/MaryAAZ)\ **Post date:** [January 15, 2021, 2:13am UTC](https://openmc.discourse.group/t/coupled-neutron-photon-transport-problem/942/1 "2021-01-15T02:13:43Z")
Hello everyone, I am trying to solve a coupled neutron-photon transport problem. In my model, I defined a neutron source and activated the photon transport (settings.photon\_transport = True). Also, I am using particle filters (‘neutron’ and ’photon’) because am tallying the flux from neutrons and photons. According to the [OpenMC documentation](https://docs.openmc.org/en/stable/methods/photon_physics.html?highlight=photon%20energy#photon-production), … “In coupled neutron-photon transport, a source neutron is tracked, and photons produced from neutron reactions are transported after the neutron’s history has terminated. Since these secondary photons form the photon source for the problem, it is important to correctly describe their energy and angular distributions as the accuracy of the calculation relies on the accuracy of this source”. For me, it is not clear how to define the energy and angular distributions of the photon source mentioned in the paragraph above. Any help regarding this topic would be very appreciated. Maria ---
**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\ **Post date:** [January 15, 2021, 8:18pm UTC](https://openmc.discourse.group/t/coupled-neutron-photon-transport-problem/942/2 "2021-01-15T20:18:11Z")
Hi @MaryAAZ and welcome to the community! Photon yields and energy distributions arising from neutron reactions are just part of the normal nuclear data libraries, so you as the user don’t need to do anything special. When neutron reactions occur that lead to the production of photons, the proper yields and energy distributions will be used accordingly. ---
**Author:** ![MaryAAZ](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/maryaaz/32/1244_2.png) [@MaryAAZ](https://openmc.discourse.group/u/MaryAAZ)\ **Post date:** [January 26, 2021, 3:20pm UTC](https://openmc.discourse.group/t/coupled-neutron-photon-transport-problem/942/3 "2021-01-26T15:20:38Z")
Thank you @paulromano. ---
**Author:** ![kevinm387](https://avatars.discourse-cdn.com/v4/letter/k/bcef8e/32.png) [@kevinm387](https://openmc.discourse.group/u/kevinm387)\ **Post date:** [January 31, 2022, 7:17pm UTC](https://openmc.discourse.group/t/coupled-neutron-photon-transport-problem/942/4 "2022-01-31T19:17:58Z")
Hello, I have a quick follow up question on this topic. In coupled neutron-photon simulations, are only prompt photons produced by neutron interactions? Or are both prompt and delayed photons produced and simulated? Thanks! ---
**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\ **Post date:** [February 1, 2022, 1:12pm UTC](https://openmc.discourse.group/t/coupled-neutron-photon-transport-problem/942/5 "2022-02-01T13:12:47Z")
In general, photons that result from the decay of transmutation products are not simulated. The one exception is for delayed photons from fission where we do have a special treatment. To account for the energy of delayed fission photons, we scale the yield of prompt fission photons that are produced by the ratio of (EGD + EGP)/EGP, where EGD is the energy of delayed gammas and EGP is the energy of prompt gammas (these come from the ENDF MF=1, MT=458 data). Here it is in code: > This treatment is on by default, but you can also manually turn it off with: ```auto settings = openmc.Settings() settings.delayed_photon_scaling = False ``` ---
**Author:** ![kevinm387](https://avatars.discourse-cdn.com/v4/letter/k/bcef8e/32.png) [@kevinm387](https://openmc.discourse.group/u/kevinm387)\ **Post date:** [February 3, 2022, 1:19am UTC](https://openmc.discourse.group/t/coupled-neutron-photon-transport-problem/942/6 "2022-02-03T01:19:05Z")
Ok great, thank you @paulromano