[KENNEDY] ON THE NUMBER OF DELTA PARTICLES EXPELLED 35 
1.e., approximately 125 delta particles left the polonium coated copper 
plate for every @ particle which it emitted. 
In seeking to interpret this result one must remember that in a 1] 
probability there were just as many @ particles shot back per secon d 
into the copper plate carrying the polonium deposit as were projecte d 
‘forward away from it. Since @ rays are known to produce secondary 
rays when they impinge on a metal it is therefore highly probable that 
a very considerable portion of the delta radiation measured in the ex- 
periments described above were secondary rays caused by these re- 
trograde @ rays. 
It follows then that before one can form an estimate of the number 
of delta particles projected with each @ ray from the particles which 
are the parent atom of the active deposit particles one must ascertain 
the number of delta particles projected as a secondary radiation from a 
copper plate, when the latter is bombarded by one 4 particle. 
From experiments which are now being made by the writer it is 
expected that this number will shortly be obtained. It will then be 
possible to make an estimate of the number of delta particles ejected 
concurrently with an @ particle in the disintegration of a radioactive 
atom. 
In conclusion, the writer wishes to express his sincere thanks to 
Professor McLennan for his helpful suggestions and for his interest in 
the investigation. 
