# Calculate the mobility of ions in a gas mixture at different atmospheric pressures (0-4MPa)

Dear Experts

Hi, I want to calculate the mobility of ions in a gas mixture at different atmospheric pressures (0-4MPa). The gas mixture is 85% argon + 15% carbon dioxide and 85% argon + 15% nitrogen.

Can Garfield++ calculate it? If it can be calculated, what formula is it based on?

Thanks!

Dear @changjh12 ,

Thank you for contacting us on the forum! I will ask @hschindl for guidance with your question.

Cheers,
Vincenzo

Hi,
apologies for the delay. For Ar/CO2 (85:15) you can use the mobility file for Ar+ ions in Ar. In reality things are quite complicated, see for instance this presentation

but the Ar+ in Ar mobility values happen to be quite close to measurements. For Ar/N2 I don’t know, but I would perhaps also use the Ar+ in Ar mobility file as a starting point.

Thank you for your reply, the mobility of gas mixtures is indeed very complex. And there’s something I don’t understand:

For Ar/CO2 (85:15) you can use the mobility file for Ar+ ions in Ar.

Do you mean by this sentence to use the Ar^+ in Ar mobility directly instead of the Ar^+ in Ar/CO2 (85:15) mobility? Or do you mean to use the Ar^+ in Ar mobility as a starting point and use Blanc’s law in Garfield++ to calculate the mobility of the gas mixture?

I read the PPT you gave and the mobility of Ar+CO2(85:15) can be calculated by Blanc’s mobility interpolation. Is there a software tool to calculate the mobility of a gas mixture?
And I have a question, does Blanc’s Law still applicable in high air pressure environment(e.g. 40atm)?

I’m new to this field and would like to ask if there is any software that can calculate the species of products after gamma particles are incident on a mixture of gases (e.g., Ar+CO2(85:15)), and if MCNP can do it?

I’m afraid I’m not at all an expert on ion mobilities, but I’ll try to answer…

• Yes, I did mean use the mobility file for Ar+ in Ar directly; as far as I know the “effective” ion mobility in this mixture happens to be quite close to these numbers.
• You can use Blanc’s law to calculate the mobility of a given ion species in a mixture of gases, but the ions can “change identity” so I’m not sure that applying Blanc’s law will give you more accurate results.
• As I said, I’m not at all an expert, but 40 atm seems high to me to reliably extrapolate mobility values to (mobilities are usually measured at very low pressure).
• I’m afraid I don’t know anything about MCNP, you should probably consult the MCNP manual or experts…