Generally in the atmosphere ion concentration is around 500 to 700 per centimeter cube.
I'm confused, are you looking to measure the ions with gammas (backscatter), or are you trying to ionize the atmosphere with gammas, and want to know what you will make?
Yaa sir i trying to ionize the atmosphere with gamma radiation and what are the ion pair produced, i want to measure the how much +ve ions and -ve ions.
You would need an instrument that produces an electric field, something like big planar condenser. Between the plates of the condenser you can pump in the atmosphere (or any other gas). When you irradiate the atmosphere with gammas (let's say you put point source of 137-Cs between the plates), the +ions and -ions would be separated by the electric field and if you connect the condenser to an instrument that measures the electrical current, you can calculate the quantity of the charges q (I=q/t) and from that calculate the number of charge carriers. I don't know if such instrument exists but this principle is used in every gas chamber detector. I believe that you can make something like this if you have the parts and an electric engineer at hand.
You would need an instrument that produces an electric field, something like big planar condenser. Between the plates of the condenser you can pump in the atmosphere (or any other gas). When you irradiate the atmosphere with gammas (let's say you put point source of 137-Cs between the plates), the +ions and -ions would be separated by the electric field and if you connect the condenser to an instrument that measures the electrical current, you can calculate the quantity of the charges q (I=q/t) and from that calculate the number of charge carriers. I don't know if such instrument exists but this principle is used in every gas chamber detector. I believe that you can make something like this if you have the parts and an electric engineer at hand.
Jelena
such instrumentation exists problem or rather an issue is that the ions get attached to aerosol particles that fully change the current characteristics in a way that such an instrument is used to assess the aerosol concentration in the air
see for instance
http://link.springer.com/article/10.1007%2FBF00879422#page-1
There are several commercially available air ion counters, most based on the Gerdien tube. Do you have a calibrated air ion counter? Are you planning on making your own? The expected number of ion pairs can be calculated from the definition of the Roentgen. To measure the Roentgen you will need a free air ionization chamber. A practical size of a free air ionization chamber is limited to gamma energies less than 1 MeV.
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