PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
325 
of all to analyse the absorption of the primary radiation into J, K, L, M, ... and S 
absorptions, the secondary corpuscular radiation into J, K, L, M corpuscular radia¬ 
tions, and the secondary X-radiations into »T, K, L, M ... and S radiations, and 
observe only the relations between the corresponding quantities, or at any rate to do 
this for one particular series, say the K series, with primary radiations of various 
wave-lengths. 
Energy of Fluorescent (Characteristic X- radiation). 
The energy of the fluorescent X-radiation was first measured and expressed in 
terms of the energy of the absorbed primary X-radiation by Barkla and Sadler.* 
In this as in all similar measurements the energies of radiations of different wave¬ 
lengths were compared by their total ionizing powers. With a primary radiation of 
wave-length considerably shorter than that of copper K radiation, the energy of 
the X-radiation emitted was about 33 per cent, of the energy absorbed, or about 
40 per cent, of the K absorption; with a primary of shortening wave-length the 
fraction diminished.! For other substances the transformation fraction was of the 
same order of magnitude. 
Sadler, | working with approximately homogeneous primary radiations, made a 
much more systematic and accurate investigation of the energy in the fluorescent 
characteristic radiations from several substances, and expressed this in terms of the 
primary energy absorption obtained by Barkla and Sadler. The results obtained are 
given in Tables I. and II. Table I. shows the fraction of the total energy absorbed 
Table I.—Giving Fraction (F K /E) of Total Primary Energy Absorbed transformed 
into Fluorescent X-radiation of Series K. 
Primary radiation. 
Wave-length 
(ai). 
Substance exposed to primary radiation. 
Cr. 
Fe. 
Co. 
Ni. 
Cu. 
Zn. 
cm. 
Fe X-radiation (series 
K) 
1 - 93 x10“ 8 
0-151 
Co 
( „ 
) 
1-78 x10~ s 
0-132 
(0-098) 
Ni 
( 
) 
1 -65 x10~ 8 
0-125 
0-216 
0-066 
Cu 
( „ 
) 
1 • 54 x10~ 8 
0-110 
0-194 
0-262 
0-080 
Zn 
( „ 
) 
1-43 x10- 8 
0-095 
0-179 
0-243 
0-289 
0-086 
As 
( „ 
) 
1-17x10~ 8 
0-067 
0-132 
0-170 
0-203 
0-248 
0-281 
Se 
( „ 
) 
1 ■ 10 x10~ s 
0-055 
0-106 
0-130 
0-163 
0-199 
0-239 
Ag 
( » 
) 
0-56 x10 -8 
0-058 
(0-105) 
(0-113) 
* ‘Phil. Mag.,’ October, 1908. 
t At the same rate as the fraction 
J ‘ Phil. Mag.,’ July, 1909. 
absorption in air 
absorption in Cu 
The range of wave-lengths, however, was short. 
2 z 2 
