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PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
radiation ; that is, for a given quantity of corpuscular radiation emitted, there is 
emitted sufficient K fluorescent radiation to produce an equal ionization. But as the 
K fluorescent radiation in this case differs little from the primary radiation, we see 
that for each K electron emitted there is also produced sufficient fluorescent radiation to 
set free another high speed electron with a velocity only just smaller than that of the 
electron ejected directly. As this electron possesses the energy of a quantum of the 
fluorescent radiation, we conclude that for each K electron emitted directly there is 
emitted also one quantum of the K fluorescent radiation. This experimental conclusion 
is so definite, so simple and significant, that we shall proceed to study the relations 
under other conditions. But before doing so we must again point out the extreme 
improbability of such an agreement by chance ; a priori the energy of fluorescent 
radiation might be that of 100 quanta or part of a quantum for each electron 
emitted, yet it is one quantum within a small possible error. 
As the wave-length n of primary radiation decreases, the energy of a quantum of 
this primary radiation increases, but the quantum of the characteristic radiation 
remains constant. If, therefore, one quantum of this characteristic radiation is still 
emitted for each high-speed electron emitted, then 
Energy of K fluorescent X-radiation _ quantum of K fluorescent radiation 
Energy of K corpuscular radiation quantum of primary radiation 
_ frequency of K fluorescent radiation _ % ^ // 
frequency of primary radiation n m k ’ 
i.e., the energy of the fluorescent radiation becomes a smaller and smaller fraction of 
that of the corpuscular radiation. This is exactly what happens, and certainly 
approximately at the theoretical rate. 
Possibly this argument is clearer as follows :— 
Total energ y of K fluorescent radiation (F K ) 
Energy of a quantum of K fluorescent radiation ( hn K ) 
= Number of quanta of fluorescent radiation (N F say), 
Total energy of K corpuscular radiation (C K ) 
Energy of a quantum of primary X-radiation (hn) 
— Number of electrons in corpuscular radiation (N c say). 
Hence the number of quanta of fluorescent radiation emitted per electron of the 
corpuscular radiation = — . 
N c C K n K 
The experimentally determined number of quanta of fluorescent radiation emitted 
for each electron in the corpuscular radiation— i.e. £d ven in the following 
table (V.) for primary radiations of various wave-lengths. These results show that 
