SUCCESSION OK CHANGKs IN RADIOACTIVE BODIES. 217 



that radium must be produced from some source, and that the present supply is 

 maintained by the continuous production of fresh radium to (Balance its rate of 

 disappearance. 



The question of possible parentage has been discussed by the writer ('Radio- 

 activity,' p. 334) and it has been shown that uranium best fulfils the conditions of 

 Ixsing the parent of indium. In the Hint place, uranium has an average life 5 X 10 s 

 years, which is very long compared with the life of radium. In addition, the activity 

 observed in pitchblende is about what would \m expected if uranium were the parent 

 of radium. If each atom of uranium in breaking up gives rise to one atom of radium, 

 the activity of the uranium and its products (measured by the at rays) would l>e aliout 

 six times that of the uranium itself. This follows since each atom of uranium in 

 breaking up gives out only one a particle, while the radium arising from it would 

 give out during its succession of changes five a particles (including the a particle from 

 radium E). 



Taking into account that actinium and thorium, as well as uranium and radium, 

 are found in pitchblende, the observed activity of about six or seven times that of 

 uranium is almost what is to be exj>ected if radium is a product of uranium. 



Now, from the data given in section 31, the amount of radium produced per year 

 on the above hypothesis can readily be calculated. The fraction of uranium clmnging 

 per year is about 2 X 10~". Assuming that the uranium passes directly through rapid 

 stages into radium, the weight of radium produced per year, per gramme of uranium, 

 would be nearly equal to the weight of uranium changed, i.e., '2 X 10~ a gramme. 

 The emanation from this quantity of radium would discharge an ordinary electroscope 

 in about 10 minutes, and thus a very small fraction of the above amount should be 

 detectable. If a kilogramme of uranium is used instead of a gramme, the amount of 

 radium produced per year is 2 X 10 ~ 6 gramme. The emanation from this amount 

 would discharge an electroscope almost instantly. The amount of radium produced 

 in a single day should be readily recognizable. 



The suggestion that uranium was a possible parent of radium was given in the 

 paper on ' Radioactive Change,' and it was arranged between Mr. SODDY and the 

 writer that the former should try experiments to ascertain whether radium were 

 produced from uranium. Mr. SODDY has published a preliminary account of his 

 experiments.* He found no evidence of the production of radium from uranium and 

 calculated that if radium were produced at all, it was certainly at less than 1/100,000 

 of the theoretical rate. 



On my part, 1 have examined both thorium and actinium to find whether radium 

 is produced from them. It was thought possible that actinium might be an 

 intermediate product between uranium and radium. The theoretical outlook for 

 thorium did not seem very promising, but the observation that some pure thorium 



* ' Nature,' May, 1904. 

 VOL. COIV. A 2 F 



