Experimentswith High Velocity Positive Ions. 229 equality of the total separations and the relatively inverted positions of the levels due to the two isotopes 199 and 201. The structure now proposed shows that the anomaly noted by Schuler and Keyston regarding the magnitudes of the isotope displacements and the fine intervals does not exist in the 6 1P1 level.In conclusion, we should like to record our deepest thanks to Professor Yenkatesachar for his guidance and encouragement throughout this work. One of us is indebted to the University of Mysore for the award of a scholarship.
It would appear to be very important to develop an additional line of attack on problems of the atomic nucleus. The greater part of our information on the structure of the nucleus has come from experiments with α-particles and if we can supplement these with sources of positive ions accelerated by high potentials we should have an experimental weapon which would have many advantages over the α-particle. It would, in the first place, be much greater in intensity than α-particle sources, since one microampere of positive ions is equivalent, so far as numbers of particles is concerned, to 180 grams of radium equivalent. It would in addition have the advantage of being free from penetrating β and γ rays which are a complication in many experiments, whilst the velocity would be variable at will. The main difficulty in obtaining such sources lies of course in the production and application of the very high potentials necessary to accelerate the particles if velocities approaching that of the α-particle are to be obtained. For example, α-particle from polonium have an energy corresponding to 5.2 million electron volts and a potential of 2.6 million volts would be required to give a helium nucleus an equal amount of energy. We have therefore to decide what is the minimum acceleration voltage at which we can usefully work, since the experimental difficulties increase very rapidly with increasing voltage. In making this decision we are naturally guided by the recent theoretical work of Gamow on the “ Theory of Artificial Disintegration.” On Gamow’s theory the probability of an α-particle of velocity
v
entering a nucleus of atomic number Z, after coming within the effective radius of the nucleus, is W =
e
-16π
e
2Z/
hv
J
k
, Where J
k
is a function varying slowly with
v
and Z. It is clear, therefore, that for particles of equal energy the lighter particle has the greater chance of penetration into the nucleus, so that we should choose protons as our source of positive ions for this reason.
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