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.
An important enlargement of the field of nuclear research has been effected by the experiments of Lawrence. Lewis, and Livingstone,* who first used the ions of the heavy isotope of hydrogen to produce nuclear disintegrations. Their pioneer experiments showed that these ions, which will in future be termed “diplons,” produced disintegrations of considerably greater complexity than those produced by protons of the same energies. Thus, Lawrence, Lewis, and Livingstone reported that from most of the substances bombarded, one or more groups of protons were emitted, whilst a group having a range of about 18 cm. appeared to be emitted from every element investigated. This surprising result led these workers to the hypothesis that the “diplon” is unstable in a strong nuclear field and that it breaks up into a proton and a neutron with a liberation of energy of the order of 5 million volts, the neutron mass being taken to be 1·0006 to explain the observed proton energies. In addition to the emission of long-range protons, Lawrence, Lewis, and Livingstone (
loc. cit.
) reported the emission of α-particles from lithium, beryllium, boron, nitrogen, magnesium, and aluminium. The experiments of Rutherford, Oliphant, and Kinsey§ and the Wilson chamber photographs of Dee and Walton║ showed that tho 13·2 cm. α-particlcs from lithium originated from the dis-integration of Li
6
into two α-particles, and suggested that Li
7
disintegrated into two α-particles and a neutron. No detailed studies have been made of the disintegration of the other elements.
The production of radioactivity by artificial means has recently been achieved by Curie and Joliot who showed that after bombarding boron, magnesium and aluminium by α-particles, positive electrons were emitted, the activity decaying with period ranging from 2 to 14 minutes. By chemical test they were further able to show that the radioactivity was due to the formation of new radioactive isotopes, radio silicon, radio nitrogen, and radio phosphorus, these bodies having half lives of 14·5, 2·5 and 3·25 minutes respectively. The suggested that it ought to be possible to produce these radioactive isotopes in other ways, and in particular that by bombarding carbon with diplons the same radioactive from of nitrogen ought to be produced.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.