Photon flux from ionization meter reading

rate of charge creation per unit volume

eq. 1

where:

charge on the electron

energy to create electron ion in air

energy flux

volume density of charge, can be expressed as Roentgens

taking the derivative

eq. 2

energy attenuation length

eq. 3

photon energy

photon flux

combine equations 1,2 and 3 (ignoring sign)

or

eq. 4

Example evaluation:

definition of Roentgen
http://nis-www.lanl.gov/~stanleym/dissertation/node16.html

~energy to ionize air

energy of gamma ray

from NIST for 150 keV gamma rays

density of air

let

= r

using eq. 4

Photon flux determined from meter reading

Seth's meter:
http://www.radcal.com/10xseries.html