# about temperature **URL:** \ **Category:** User Support\ **Created:** [November 26, 2015, 7:26am UTC](https://openmc.discourse.group/t/about-temperature/185 "2015-11-26T07:26:57Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![niuoba](https://avatars.discourse-cdn.com/v4/letter/n/f04885/32.png) [@niuoba](https://openmc.discourse.group/u/niuoba)\ **Post date:** [November 26, 2015, 7:26am UTC](https://openmc.discourse.group/t/about-temperature/185/1 "2015-11-26T07:26:57Z")
Hi all: Is there any feasibility for me to indicate a temperature for a specific isotopic in materials.xml, and get this isotopic’s cross-section? (For example a key words “temperature”) ---
**Author:** ![khurrum](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@khurrum](https://openmc.discourse.group/u/khurrum)\ **Post date:** [November 27, 2015, 4:53am UTC](https://openmc.discourse.group/t/about-temperature/185/2 "2015-11-27T04:53:03Z")
Hi, If i may jump in… When we define a nuclide or element in materials.xml file, we can specify “default\_xs” which will assign same cross section (temperature) to all the materials. one way to over-ride this is to define a “xs” attribute with each one where this attribute will point towards the correct temperature cross section file. ```auto here material 1 is at 293K (stored in files with .02c) while uranium-235 is at 300K (stored in files with .03c). Hope that helps. ``` ---
**Author:** ![niuoba](https://avatars.discourse-cdn.com/v4/letter/n/f04885/32.png) [@niuoba](https://openmc.discourse.group/u/niuoba)\ **Post date:** [November 27, 2015, 6:22am UTC](https://openmc.discourse.group/t/about-temperature/185/3 "2015-11-27T06:22:12Z")
Thank you Khurrum for your kindly help. It’s very nice of you. I understand “xs” can provide cross-section based on the nuclear data. My question is, for example I want to use U-235 cross-section data which temperature is 552K. Does OpenMC have a interpolation for nuclear cross-section data, as a key word temperature=“XXX.XXXe-08” in materials.xml, which can obtain a isotopic cross-section based on user defined temperature? ---
**Author:** ![khurrum](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@khurrum](https://openmc.discourse.group/u/khurrum)\ **Post date:** [November 28, 2015, 5:26am UTC](https://openmc.discourse.group/t/about-temperature/185/4 "2015-11-28T05:26:31Z")
O sorry I misunderstood your question. To the best of my knowledge there is no function in place for it in openmc yet. For such cases I am using linear interpolation i.e. Using appropriate weightage of 500 and 600 Kelvin libraries. Or you can always generate your own cross section at 552 Kelvin :). Hope this can help. ---
**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:** [November 29, 2015, 2:49am UTC](https://openmc.discourse.group/t/about-temperature/185/5 "2015-11-29T02:49:28Z")
Khurrum is correct; there is currently no method to interpolate cross sections between two temperatures at which tabulated cross sections exist. We (i.e. MIT) are currently working on a methodology for evaluating cross sections at any temperature on-the-fly using a multipole representation. If you are interested in the details, please see the following journal article: [http://dx.doi.org/10.1016/j.jcp.2015.08.013](http://dx.doi.org/10.1016/j.jcp.2015.08.013) ---
**Author:** ![niuoba](https://avatars.discourse-cdn.com/v4/letter/n/f04885/32.png) [@niuoba](https://openmc.discourse.group/u/niuoba)\ **Post date:** [November 29, 2015, 9:18am UTC](https://openmc.discourse.group/t/about-temperature/185/6 "2015-11-29T09:18:31Z")
Thank you Dear Khurrum and Prof.Paul, I will work hard and learn more details from the journal article you provide me. My question about fixed source problem confused me a lot and still not be replied, could you help me and give me some advise?