# Source Strength

**URL:** <https://openmc.discourse.group/t/source-strength/1975>\
**Category:** User Support\
**Created:** [April 24, 2022, 11:39pm UTC](https://openmc.discourse.group/t/source-strength/1975 "2022-04-24T23:39:48Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![A66](https://avatars.discourse-cdn.com/v4/letter/a/ecae2f/32.png) [@A66](https://openmc.discourse.group/u/A66)\
**Post date:** [April 24, 2022, 11:39pm UTC](https://openmc.discourse.group/t/source-strength/1975/1 "2022-04-24T23:39:48Z")

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Hi,  
Should we always set the source strength value to 1 when writing source properties?  
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:** [April 25, 2022, 2:53am UTC](https://openmc.discourse.group/t/source-strength/1975/2 "2022-04-25T02:53:42Z")

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The [default source strength](https://docs.openmc.org/en/stable/io_formats/settings.html#source-element) is 1, so it’s not necessary to set it explicitly if you just want the default.

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<div class="post-metadata">

**Author:** ![A66](https://avatars.discourse-cdn.com/v4/letter/a/ecae2f/32.png) [@A66](https://openmc.discourse.group/u/A66)\
**Post date:** [April 25, 2022, 11:06pm UTC](https://openmc.discourse.group/t/source-strength/1975/3 "2022-04-25T23:06:55Z")

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I’m using a gamma source with radius 1. If I don’t want to set the source strength as the default 1, how can I do that if I want to specify the actual source strength.Should I use this formula?  
 ![image](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/5/5ff98f0721a6a87283c5e6abb72196cc15b49347.png)

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<div class="post-metadata">

**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:** [April 29, 2022, 12:20pm UTC](https://openmc.discourse.group/t/source-strength/1975/4 "2022-04-29T12:20:10Z")

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That formula is just telling you the flux at some distance away from an isotropic source. You would want to specify S0 for the sake of a particle transport simulation. In OpenMC, this is done with:

```python
source = openmc.Source()
source.strength = ... # your value for S_0
# specify space, angle, energy distribution of source as needed

settings = openmc.Settings()
settings.source = [source]

```