# thermal scattering data

**URL:** <https://openmc.discourse.group/t/thermal-scattering-data/400>\
**Category:** User Support\
**Created:** [February 6, 2019, 3:43pm UTC](https://openmc.discourse.group/t/thermal-scattering-data/400 "2019-02-06T15:43:08Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Tang\_Qi](https://avatars.discourse-cdn.com/v4/letter/t/49beb7/32.png) [@Tang\_Qi](https://openmc.discourse.group/u/Tang_Qi)\
**Post date:** [February 6, 2019, 3:43pm UTC](https://openmc.discourse.group/t/thermal-scattering-data/400/1 "2019-02-06T15:43:08Z")

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Hello. I know if I have a moderating material like water , I should assign thermal scattering data , such as water.add\_s\_alpha\_beta(‘c\_H\_in\_H2O’) .

MCNP is also used. When I encountered the thermal scattering data of poly.01t (Hydrogen in Polyethylene) in MCNP, how should I express it in Openmc? Thank you!

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**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 6, 2019, 4:26pm UTC](https://openmc.discourse.group/t/thermal-scattering-data/400/2 "2019-02-06T16:26:00Z")

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In this case, the correct identifier is c\_H\_in\_CH2. Note that when you use the add\_s\_alpha\_beta() method, it will automatically try to figure out the correct name even if you pass a name that is not in the correct format. It is also aware of most of the common MCNP cross section names, so if you do run add\_s\_alpha\_beta(‘poly’), it knows that you are trying to specify H in polyethylene:

> > > import openmc  
> > > m = openmc.Material()  
> > > m.add\_s\_alpha\_beta(‘poly’)  
> > > /home/romano/openmc/openmc/material.py:593: UserWarning: OpenMC S(a,b) tables follow the GND naming convention. Table “poly” is being renamed as “c\_H\_in\_CH2”.  
> > > warnings.warn(msg)

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**Author:** ![Tang\_Qi](https://avatars.discourse-cdn.com/v4/letter/t/49beb7/32.png) [@Tang\_Qi](https://openmc.discourse.group/u/Tang_Qi)\
**Post date:** [February 6, 2019, 6:01pm UTC](https://openmc.discourse.group/t/thermal-scattering-data/400/3 "2019-02-06T18:01:53Z")

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Thank you for the information!

Paul Romano \<[paul.k.romano@gmail.com](mailto:paul.k.romano@gmail.com)\> 於 2019年2月7日 週四 上午12:26寫道：