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A sensitive method of measuring small ionization currents is described, and the effect of secondary beta radiation upon ionization measurements of gamma radiation is examined. It is shown that if ionization chambers made of light-atom materials have walls less than 4.0 mm. thick, secondary beta radiation is recorded so that readings are in excess of the true values. The results explain some discrepancies found by other workers.

Experiments are described which show that the electronic emission from a sheet of material, due to gamma radiation, depends upon the direction of the radiation with respect to the sheet. In certain directions, the emission from a sheet of material is equivalent to that from a sheet of "air-wall" material (graphite). An approximate explanation of these findings is given. An examination of the electronic emission from bone, when it is irradiated with gamma radiation, indicates how the energy absorption per rontgen of gamma radiation may change at boundaries between bone and soft tissues.