940 ADVENTURES IN RADIOISOTOPE RESEARCH 



ment of these discoveries, we prepared the radioactive phosphorus 

 isotope ^-P by neutron bombardment of carbon disulphide and used 

 this isotope in collaboration with Chiewitz^**^^ in the study of phos- 

 phorus metabolism. In these experiments, 10 litres of carbon disulphide 

 were used to absorb most of the neutrons emitted by a mixture of radium 

 and beryllium kindly put at our disposal by Professor Niels Bohr. 

 This precious neutron source being a gift by his friends to his fiftieth 

 birthday. The ^^p formed was extracted by treatment with diluted 

 nitric acid or with water, the carbon disulphide being immediately 

 available after the extraction for further neutron irridation. 



A few other radioactive isotopes, such as the radio-halogens can also 

 be prepared by similar simple and convenient procedures. This is, how- 

 ever, not the case with the majority of radioactive isotopes. These 

 were prepared in amounts sufficient to be utilized in indicator-work 

 only after the discovery of the cyclotron^^^\ Lawrence's highly 

 significant discovery also made available radiophosphorus preparations 

 of very much greater activity than could be obtained from neutron- 

 sources containing as much as several grams of radium. The number 

 of neutrons produced by the Berkeley cyclotron was stated by Birge**^^ 

 in 1939 to correspond to the number of ions produced by 100 kgm 

 of radium ; since that date, a still more powerful cyclotron has been 

 brought into use. In our later investigations, radiophosphorus gener- 

 ously put at our disposal by Professor Niels Bohr, Lawrence and 

 Siege ahm was used. 



The preparations of radioactive isotopes of numerous elements pre- 

 pared in the Radiation Laboratory at Berkeley and in other laboratories 

 found an extended application as indicators. Radioactive iron prepared 

 at Berkeley, for example, was used by Hahn, Whipple and their 

 colleagues^*^^ in extended studies of iron metabolism. 



The application of cyclotron-prepared radio-carbon*'^^^ revolutionized 

 our views of the fundamental process of photosynthesis. 



Radio-iodine**'^' found an extended application in the study of the 

 formation of thyroxine and diiodotyrosine ; it led, inter alia, to the 

 important finding that some thyroxine is formed in the organism even 

 after total extirpation of the thyroidea.**^' 



Radio-phosphorus found, however,** '^ the most extensive applica- 

 tion. This was due not only to the convenient mode of production and 

 period of decay of this material, together with the convenient absorba- 

 bility of the rays emitted by it, but mainly to the important part which 

 phosphorus plays in a very great number of metabolic processes. These 

 include skeleton formation, metabolism of carbohydrates and fats, cell 

 division, and many other processes. The discussion of the role of phos- 

 phorus in metabolic processes is therefore well-suited to demonstrate 

 different applications of isotopic indicators in biological research. We 



