50 



BIOLOGICAL EFFECTS OF RADIATION 



values; hence one beam might have shorter wave-lengths, not present 

 at all in the other. However, the proved equivalence, where the peak 

 voltages are very different, signifies that while there are some shorter 

 wave-lengths in one spectrum than in the other, they are present to a 

 negligible extent. As the peak value of an exciting voltage approaches 

 the equivalent constant voltage, it signifies that the energy in the shorter 

 wave-lengths becomes relatively greater. This, however, is taken care 

 of in the specification of quality by the fact that for a given peak voltage, 

 if the shorter wave-lengths gain in importance, the equivalent voltage 

 is correspondingly increased. For example, with X-rays produced by 

 mechanical, full-wave, or Villard rectifiers (Fig. 1) operated at the same 



Table 1.— Absorption of General X-radiation in Copper 



(Tube wall 1.29 mm. cerium glass) 



/„ - incident radiation; / - transmitted radiation; IOO///0 = percentage transmission 



100 kv. 



110 kv. 



120 kv. 



Copper filter, 

 (mm.) 







0.14 



0.20 



0.25 



0.30 



0.40 



0.50 



0.75 



1.00 



1.60 



2.00 



2.60 



3.00 



100 

 I/It, 



100 

 20.40 

 15. 3S 

 12. 8S 

 11.15 

 8.78 

 7.16 

 4.53 

 3.08 

 1.77 

 1.03 



log 

 100 



I/Io 



100 



I/Io 



00 

 310 

 187 

 110 

 047 

 943 

 854 

 656 

 489 

 .248 

 013 



100 



22. 



17. 



15 



13 



10 



8 



5 



4 



2 



1 



1 



08 

 S4 

 18 

 17 

 28 

 50 

 77 

 13 

 42 

 ,60 

 .02 



log 

 100 



I/Ia 



100 

 I/Io 



00 

 344 

 251 

 181 

 120 

 012 

 924 

 761 

 .616 

 384 

 210 

 .009 



100 



23. 



19. 



17. 



15. 



12, 



10, 



7 



5 



3 



2 



1 



1 



log 

 100 

 I/Io 



130 kv. 



80 

 92 

 37 

 23 

 12 

 05 

 04 

 18 

 13 

 06 

 46 

 09 



100 

 I/Io 



00 

 377 

 299 

 240 

 183 

 084 

 002 

 848 

 714 

 496 

 314 

 164 

 ,037 



100 



25. 



21. 



19. 



17, 



13 



11 



8 



6 



4 



2 



2 



1 



S2 

 81 

 19 

 00 

 75 

 57 

 32 

 35 

 00 

 73 

 00 

 ,48 



log 

 100 



I/Io 



140 kv. 



100 

 I/Io 



00 100 



412 

 339 

 283 

 230 

 138 

 063 

 920 

 803 

 602 

 .436 

 .301 

 170 



27 



23 



20 



18 



15 



13 



9 



7 



4 



3 



2 



1 



log 

 100 

 I/Io 



150 kv. 



.65 

 AS 

 85 

 71 

 37 

 06 

 55 

 41 

 ,86 

 .38 

 .50 

 .93 



100 



I/Io 



00 



442 



370 



319 



267 



187 



116 



980 



870 



.687 



.529 



398 



.286 



100 



30. 



25, 



22 



20 



16 



14 



10 



8 



5 



4 



3 



2 



log 

 100 



I/Io 



35 

 68 

 85 

 55 

 98 

 AZ 

 ,65 

 .43 

 .75 

 .13 

 .12 

 .49 



2.00 



1.482 



1.410 



1.359 



1.313 



1.230 



1.159 



1.029 



0.926 



0.760 



0.616 



0.494 



0.396 



Note: All second-place decimal figures given in italics are approximate values. 



peak values, the equivalent voltage approaches respectively nearer the 

 peak value, indicating an increasing relative intensity of the shorter 

 wave-lengths. Correspondingly, it is found that the absorption curves 

 indicate respectively harder composite radiations after the same mitial 



filtration. ^ .,,,., 1 ^.^ 



It is also to be expected that two beams which yield hke absorption 

 curves with a low or moderate initial filtration [up to 1.5 mm. Cu at 150 

 kv. (constant)], may, after a higher initial filtration, furnish somewhat 

 divergent curves— the curve for the radiation having the higher peak 

 voltage falling above the other. By matching the curves above the point 

 corresponding to the initial filtration, however, a new eqmvalent voltage 



