PRESENT PROBLEMS OF RADIOACTIVITY 



BY ERNEST RUTHERFORD 



[Ernest Rutherford, Macdonald Professor of Physics, McGill University, Montreal. 

 b. August 30, 1871, Nelson, New Zealand. M.A. and D.Sc. University of New 

 Zealand; B.A. Cambridge, England; F.R.S. 1903; F.R.S.C. 1899; post- 

 graduate, Cambridge, England, 1895-98; Professor of Physics, McGill Univer- 

 sity, Montreal, 1898. Member of American Physical Society, and others; 

 awarded Rumford Medal of the Royal Society, 1904. Author of books and 

 articles.] 



SINCE the initial discovery by Becquerel of the spontaneous emis- 

 sion of new types of radiation from uranium, our knowledge of the 

 phenomena exhibited by uranium and the other radioactive bodies 

 has grown with great and ever increasing rapidity, and a very large 

 mass of experimental facts has now been accumulated. It would be 

 impossible within the limits of this article even to review briefly the 

 more important experimental facts connected with the subject, and, 

 in addition, such a review is rendered unnecessary by the recent pub- 

 lication of several treatises 1 in which the main facts of radioactivity 

 have been dealt with in a fairly complete manner. 



In the present article, an attempt will be made to discuss the more 

 important problems that have arisen during the development of the 

 subject and to indicate what, in the opinion of the writer, are the 

 subjects which will call for further investigation in the immediate 

 future. 



II. Nature of the radiations 



The characteristic radiations from the radioactive bodies are very 

 complex, and a large amount of investigation has been necessary to 

 isolate the different kinds of rays and to determine their specific 

 character. The rays from the three most studied radio-elements, 

 uranium, thorium, and radium, can be separated into three distinct 

 types, known as the a, /?, and f rays. 



The nature of the a and /? rays has been deduced from observations 

 of the deflection of the path of the rays by a magnetic and electric 

 field. According to the electromagnetic theory, a radiation which 

 is deflectable by a magnetic or electric field must consist of a flight of 

 charged particles. If the amount of deflection of the rays from their 

 path is measured when both a magnetic and an electric field of known 



1 Mme. Curie, Theses presentees a la Faculte des Sciences. Paris, 1903. 

 H. Becquerel, Recherches sur une propriety nouvelle de la Matiere. Typographic 

 de Firmin, Didot et Cie. Paris, 1903. 



E. Rutherford, Radioactivity. Cambridge, University Press, 1904. 



F. Soddy, Radioactivity. Electrician Co., London, 1904. 



