# Computing the fission neutron energy spectrum

**URL:** <https://openmc.discourse.group/t/computing-the-fission-neutron-energy-spectrum/207>\
**Category:** User Support\
**Created:** [April 9, 2016, 2:29pm UTC](https://openmc.discourse.group/t/computing-the-fission-neutron-energy-spectrum/207 "2016-04-09T14:29:09Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Mohamed](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@Mohamed](https://openmc.discourse.group/u/Mohamed)\
**Post date:** [April 9, 2016, 2:29pm UTC](https://openmc.discourse.group/t/computing-the-fission-neutron-energy-spectrum/207/1 "2016-04-09T14:29:09Z")

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Hello everyone  
I just work with OpenMC multi group mode  
I computed all the cross sections in each group of energy for the use in the file mg\_cross\_sections.xml but I can’t calculate the neutron fission spectrum from a term OpenMC  
Could anyone help me  
Regards

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**Author:** ![Will\_Boyd](https://avatars.discourse-cdn.com/v4/letter/w/90ced4/32.png) [@Will\_Boyd](https://openmc.discourse.group/u/Will_Boyd)\
**Post date:** [April 9, 2016, 2:33pm UTC](https://openmc.discourse.group/t/computing-the-fission-neutron-energy-spectrum/207/2 "2016-04-09T14:33:14Z")

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Mohamed,

Consider this post to a previous thread about computing the fission matrix:

[https://groups.google.com/d/msg/openmc-users/F6kCBG1BX6s/0qaL7a9GFwAJ](https://groups.google.com/d/msg/openmc-users/F6kCBG1BX6s/0qaL7a9GFwAJ)

This details how to compute the fission spectrum using the fully documented “openmc.mgxs” module.

Best,  
Will