CHEMICAL DETECTION OF ARTIFICIAL TRANSFORMATION OF ELEMENTS

The first artificial transformation of elements was detected by the protons that are emitted in the process of transformation (Rutherford, 1919). Recently, in connection with the study of artificial radioactivity (Curie and Joliot, Fermi with collaborators), methods of radiochemistry, combining radioactive measurements and chemical operations, have been applied to the direct determination of the chemical nature of the newly arising elements. In a recent note Paneth and Loleit* report the results of the chemical detection of the artificial transformation of boron when it is irradiated with slow neutrons. In the authors’ experiments, boromethyl ether placed in a spherical copper vessel was irradiated with slow neutrons from a source \(Rn + Be\), located in the central part of the ves-

* Paneth a. Loleit. Nature, 136, 950, 1935.

vessel; in this process the neutrons were slowed by collisions with the protons of the irradiated ether and the water surrounding the vessel. The slow neutrons, being captured by boron nuclei, caused their disintegration according to the following reaction:

\[ {}^{10}_{5}\mathrm{B}+{}^{1}_{0}\mathrm{n}\to{}^{7}_{3}\mathrm{Li}+{}^{4}_{2}\mathrm{He} \]

In the experiment, the helium arising as a result of this reaction was determined. In the first experiment there was a source of 450 millicuries of emanation; in this case an amount of helium sufficient for its spectroscopic detection was obtained. In the second experiment, which continued for seven weeks, 2,200 millicuries of emanation decayed. As a result, an amount of helium was obtained sufficient not only for spectroscopic detection but also for its measurement. The measurements showed that \(1.3\cdot 10^{-7}\ \mathrm{cm}^{3}\) of helium was formed (measurement accuracy 20%). Control experiments, carried out under the same conditions for 9 weeks but without a neutron source, revealed a complete absence of helium. Therefore the appearance of helium must be ascribed to the destruction of boron by neutrons. From the measured amount of helium one can estimate the number of neutrons emitted by the given \( \mathrm{Rn}+\mathrm{Be} \) source, assuming that the creation of one helium atom requires one neutron. Such calculations showed that 1 millicurie of radium emanation with beryllium emits more than 3,000 neutrons per second; in these calculations it is assumed that not more than half of the neutrons formed in the source are absorbed by the boron inside the vessel. At present the authors are carrying out further experiments in this direction. They believe that direct chemical detection of the products of artificial transformation of elements is also possible in a number of other cases.

L. Groshev, Moscow