66 BIOLOGICAL EFFECTS OF RADIATION 



France have drawn up certain recommendations (57) on the technique of 

 measuring the roentgen. 



THE MEASUREMENT OF QUALITY 



X-ray Quality (Hardness, Spectral Distribution).— The term X-ray 

 quahty relates to the composition of an X-ray beam as determined by 

 the spectral range and energy distribution. In the case of homogeneous 

 X-rays, the quality may be expressed in terms of the wave-length of the 

 radiation, measured in Angstrom units (1 A = 10-« cm. = 1000 X.U.). 

 In the case of the heterogeneous X-rays which occur in practice, a conven- 

 ient practical classification quality is given below: Following the desig- 

 nation of the rays, there are given in order, first the approximate range 

 of applied potential (kilovolt peak), and then the equivalent end-radi- 

 ation limits in Angstroms, thus, 



o 



Ultra-soft Grenz radiation, 5 to 10 kv., 2.5 to 0.6 A. 



Soft radiation for diagnostic work and superficial therapy, 20 to 120 kv., 0.6 



to 0.1 A. ^or 5 



Hard radiation for deep therapy, 120 to 250 kv., 0.1 to 0.05 A. 

 Extra-hard or super-hard radiation for highest potential therapy, over 250 kv., less 



than 0.05 A. 



Quality Specification.— In medical practice it is not convenient to 

 express the quality of heterogeneous radiation in terms of its spectral 

 distribution. The quality may, however, be expressed with sufficient 

 accuracy for such purposes by a statement of generating conditions and 



absorption data, e.g. : 



A. Generating conditions: (a) The target material. (6) Either the 

 peak or r.m.s. value of the potential applied to the X-ray tube, (c) The 

 potential wave form {e.g., constant or pulsating), {d) The type of 



filtration. 



B. Absorption data: (o) Form of the total absorption curve m cellu- 

 loid for ultra-soft radiation (5 to 29 kv.) ; aluminum for soft radiation 

 (20 to 120 kv.) ; copper for hard radiation (100 to 250 kv.) ; copper or lead 

 for ultra-hard radiation (above 250 kv.). (6) Frequently, it is sufficient 

 for practical purposes to state the thickness in millimeters of absorbmg 

 material (celluloid, aluminum, copper or, lead) which, by insertion m 

 the beam of radiation reduces the irradiation— ionometric intensity— 

 to one-half (half-value layer). 



MEASUREMENT OF THE ROENTGEN 



Recent international comparison has shown that an agreement to 

 within at least ± 1 per cent is attainable between the standard X-ray 

 dosage measurements of the participating laboratories. The following 



