The: signal charge loss due to initial recombination and that due to volume
recombination have been measured separately using parallel plate ionizatio
n chambers irradiated with cobalt-60 gamma rays, over a wide range of appli
ed voltage and air humidity. It is shown that. both initial and volume reco
mbination depend on the electric field strength and also on humidity throug
h ion clustering reaction with water molecules. in spite of the usual assum
ptions, a linear relation has not been observed between the inverses of the
signal current and applied voltage for initial recombination, nor between
the inverses of the signal current and square of the applied voltage for vo
lume recombination. Methods and data which can be used for estimation of in
itial and volume recombination losses of ions in ionization chambers; are p
roposed.