LAMINAR LESIONS IN CEREBRAL CORTEX 



365 



MILS ALUMINUM 5 

 189 177 



4 8 ENERGY OF 



DEUTERON IN MEV 



Fig. 6. Bragg ionization curve. Relative ionization produced by tiie beam of deuter- 

 ons in a thin ionization chamber after passage through ahmiinum foil of varying 

 thickness. The actual energy of the particles, as delivered by the cylcotron, was slightly 

 higher than 20 Mcv. Since, however, some absorbers had to be introduced into the 

 beam path to make the determinations shown, the first value for relative ionizations 

 is given for deutcrons of 18.9 Me\- energy. Ordinate: amount of ionization current in 

 arbitrary units per constant nimiber of incident deuterons. Abscissa: upper row of 

 figures: thickness of aluminum foil in mils; lower row of figures: the remaining energy 

 of deuterons in Mev after passage through aluminum foil of stated thickness. 



The first oroiip of problems is teclmical. We have used for calibration 

 purposes measurements of radioacti\ity induced by irradiations of copper 

 and lead discs. It was necessary to introduce correction factors for the non- 

 linearity of the ion chamber and for the scatter of the beam. 



Assuming," that our calibrations are reasonably satisfactory, it is possible to 

 express each irradiation dose as the nianhcr of diutcrons per cm-. Since 

 knowlcdoe of the number of deuterons per cm- is essential for expressing the 

 dose in any other way, it is apparent that this number is a straightforward 

 measurement of the radiation dose. From a biologic point of view, the dose 

 so expressed permits a reasonable estimate of the number of ions per imit 

 area which may be relatively harmless, injurious, or lethal for a neuron or 

 nerve fiber. Oiu' data suggest that mild to hea\y laminar lesions are produced 

 by doses of 4 x 10" to 12 x 10'' deuterons per cm'-, respectively. 



The basic disad\antage in expressing the dose as a number of deuterons 



