TABLE I 



Ion Density Proouced by Different Ionizing Particles 



RADIATION 



MODE OF GENERATION 



MEAN 

 LINEAR 



ION 

 DENSITY 



(ions per 



micron 



of tissue) 



J Theoretical minimum ion density for any particle -6 •^~ 



Very high energy 20-30 million volt betatron Fp ^ 



beta and gamma Natural ana artificial rbclioelements,\ °''^ 



radiation. *- 



Gamma Radium screened by at least _ // 



rod iation 0'5 mm, pbtinum as used m radiotherapy 



'Supervoltage "lOOOk V installation 15 



"Deep Therapy 200 kV installation QO 



X-ray tubes, operated at 30-180 kV-. _ 100 

 "Characteristic' X rays Cyclotrons 



Copper K (8 kVU—y^'^l-^"- 



X radiation — 



Neutron 

 radiation 



-Silver Li 3 kV). 



.146 

 12 million volts 290 — 



.300 



8 million volts 380 — 



..4S0 



_ Aluminium K(l-5kV) -^ - 



High-voltage ion tubes 

 - 900 kV Deuterium ions bomt)arding lithium 840 



—400kVDeutenum ions bombarding deuterium- _ 1100 ■ 



IONIZING 

 PARTICLE 



Electron 



— Proton 



Alpha . 

 radiation 



.3700 

 .4500 



Natural disintegration of radon 



Natural disintegration of poionium „ 



Artificial disintegration c/ boron or 



lithium by s/onv neutrons 9000 



Atomic rays 



. Alpha 

 particle 



Uranium fissure 130.000 -, 



Atomic 

 particle 



As an ionizing particle slows clown, it produces ions at an ever-increasing rate 

 until it has been brought nearly to rest. The ion density, therefore, increases 

 along the length of the track of any ionizing particle. The figures quoted in the 

 table are average values for all the particles generated by a given type of radiation. 

 It will be seen that this average value increases with decreasing voltage for each- 

 type of particle. Thus very high voltage X-rays give rise to the particles of lowest 

 ion density, and high-energy neutron radiation is less densely ionizing than low. 



118 



