# Need Help Co-60 Shielding Mcnp Activity Input

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## Main Question or Discussion Point

Greeting,

I am trying to figure out how can I include the activity of a Co-60 source in MCNP code.
I have the following problem Co-60 source in a cylinder surrounded by concrete. I just need to know how to include the source activity and whether it should be in Bq or Ci.

Thank you in advance

## Answers and Replies

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gleem
Science Advisor
Education Advisor
I'm not exactly sure how to answer your question for I know little how Monte Carlo calcs are actually carried out but activity is a measure of disintegrations per unit time the Becquerel being the most transparent as 1 Bq = 1 dist/sec. where as  Curies is 3.7E10 dps. The activity represents the initial strength of the flux of photons whose history is to be developed. So chose an activity that gives enough photons.that will participate in your scenario..

I'm not exactly sure how to answer your question for I know little how Monte Carlo calcs are actually carried out but activity is a measure of disintegrations per unit time the Becquerel being the most transparent as 1 Bq = 1 dist/sec. where as  Curies is 3.7E10 dps. The activity represents the initial strength of the flux of photons whose history is to be developed. So chose an activity that gives enough photons.that will participate in your scenario..
Thank you for your reply. I'm trying to figure out where and how to add it to my code more specifically how to add it to the material card
If you have an example of the material section with activity identified, please share. Thank you.

gleem
Science Advisor
Education Advisor
I'm not exactly sure how to answer your question for I know little how Monte Carlo calcs are actually carried out
It sound like you are asking a question that should be answered in the documentation.

It sound like you are asking a question that should be answered in the documentation.
What documentation, are you referring to the manual?
Well, the manual doesn't specify how to input a source activity.

Thanks for your help.

gleem
Science Advisor
Education Advisor
Are you sure you need the activity as input and not just the spectrum of gammas from a given decay?

Are you sure you need the activity as input and not just the spectrum of gammas from a given decay?
Ok, so here is what I m trying to simulate, from left to right, Co-60 with an activity of 1 Ci in a cylindrical cask, concrete wall 2 ft away from the source, then detector. I need to find the dose behind the concrete wall using mcnp. I am new to MCNP and I m trying to learn it but got stuck on the activity portion.

gleem
Science Advisor
Education Advisor
Check out this primer on MCNP http://cmpwg.ans.org/mcnp/primer.pdf

If you needed the activity you would also need the half -life. In the calculation you generate a radiation emission (decay) and follow its history to a specific location AFAIK. You continue to generate these emissions until you achieve a specified precision in the specified units of interest. You do not need to specify activity since you only need to generate enough decays to get a result that you want. From the result you know the number of disintegrations that produced that result from which you determine the activity. You can then scale the activity to determine the effect for that activity.

mfb