THE MEASUREMENT OF EXTRA HARD X-RAYS AND GAMMA RAYS IN ROENTGENS

The intensity in roentgens per second of X-rays or γ-rays harder than 0.03 Å may be measured with a small thimble chamber with homogeneous walls of elements below atomic number 13 and thick enough to be impermeable to the fastest secondary β-rays. The ionization current measured under saturation conditions at standard temperature and pressure is divided by BV, and correction is made for the apparent absorption of the X-rays m the walls. V is the volume of the chamber and B is given by[Formula: see text]A table (Table IV) of the values of 2 loge (Zw/Za) for different wall materials is given, and J, K, and L are plotted (Fig. 2) as functions of the quality of the radiation.The absolute intensity of radiation in quanta per square centimetre per second may be obtained from[Formula: see text]in which c is the ionization current per unit volume in the chamber, at standard temperature and pressure, produced by one quantum per square centimetre per second.The intensity of the radiation from one milligram of radium in equilibrium, and covered by platinum of wall thickness t, at one centimetre distance is (8.98 − 1.17 mm.−1 × t) roentgens per hour approximately, it t is not less than 0.3 mm.