Positive-Ray Analysis of Potassium, Calcium and Zinc

Isotopes of potassium, calcium and zinc have been determined by positive-ray analysis, using the apparatus and method previously described in which the charge deflected by a constant magnetic field through a fixed slit into a Faraday cylinder is measured as a function of the voltage accelerating the rays. Curves showing maxima corresponding to the various isotopes are reproduced. With potassium, isotopes with atomic weights 39 and 41 were found as previously observed by Aston. With pure calcium isotopes at 40 and 44, and with zinc isotopes at 64, 66, 68, and 70 were observed. After a disturbing effect of the electric field was eliminated, the ratio of the intensities obtained, 18 to 1 for the two isotopes of potassium and 70 to 1 for those of calcium, gave average atomic weights agreeing well with accepted values, 39.10 and 40.07 respectively. It is pointed out that when the determination of the relative proportions of all the isotopes of an element is made sufficiently accurate and reliable, a comparison between calculated and observed average atomic weights would give a measure of the packing effect or divergence of the weights of the isotopes from integral values. If the width of the slit used in limiting the beam of canal rays were reduced from 0.37 to.07 mm., isotopes of elements of atomic weight 100 or more should be resolved with the present apparatus.