# Scattering rate tally

**URL:** <https://openmc.discourse.group/t/scattering-rate-tally/2127>\
**Category:** User Support\
**Created:** [June 16, 2022, 11:42pm UTC](https://openmc.discourse.group/t/scattering-rate-tally/2127 "2022-06-16T23:42:44Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![zhangmeithing.zmt](https://avatars.discourse-cdn.com/v4/letter/z/f9ae1b/32.png) [@zhangmeithing.zmt](https://openmc.discourse.group/u/zhangmeithing.zmt)\
**Post date:** [June 16, 2022, 11:42pm UTC](https://openmc.discourse.group/t/scattering-rate-tally/2127/1 "2022-06-16T23:42:44Z")

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Hello all,

Is it possible to obtain scattering source term using scattering rate tally? I could not find any information about the scattering rate unit. Based on OpenMC documentation, all tally scores are normalized per source. What should I do if the source rate is unknown?

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**Author:** ![pshriwise](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/pshriwise/32/3863_2.png) [@pshriwise](https://openmc.discourse.group/u/pshriwise)\
**Post date:** [June 22, 2022, 6:23am UTC](https://openmc.discourse.group/t/scattering-rate-tally/2127/2 "2022-06-22T06:23:30Z")

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Hi @zhangmeithing.zmt,

Thanks for the query!

Regarding the scores units, I’ll point you to the section on scores in the documentation

[https://docs.openmc.org/en/stable/usersguide/tallies.html#id2](https://docs.openmc.org/en/stable/usersguide/tallies.html#id2)

The `"scattering"` score is in units of `scatter / source-particle` like the other reaction rate scores.

As for normalization of this score, I’ll direct you to this section in the documentation on tally normalization

[https://docs.openmc.org/en/stable/usersguide/tallies.html#normalization-of-tally-results](https://docs.openmc.org/en/stable/usersguide/tallies.html#normalization-of-tally-results)

Note that for eigenvalue problems this will require additional tallies on the problem to determine the fission rate as well as the heat deposition and number of neutrons emitted per fission event. If you find this section unclear, please reach out for additional info. There’s also an exampl [here](https://github.com/openmc-dev/openmc-nea-course/blob/main/notebooks/05-tallies-i/Solution/Tallies.ipynb) near the end that you may find useful.

Patrick