n ------ dh ,
ρ
where n is a constant.
If the depth of the ionization vessel be b, the total number of ions produced in the vessel is
This supposes that the stream of particles passes completely across the vessel. If not, the expression becomes
If the ionization in the vessel AB is measured, and a curve plotted showing its relation to h, the curve in the former case should be a straight line whose slope is nb/ρ and in the latter a parabola.
Thus if a thin layer of radio-active material is employed and a shallow ionization vessel, the ionization would be represented by a curve such as APM ([Fig. 40]), where the ordinates represent distances from the source of radiation, and the abscissae the ionization current between the plates AB.
