XV. ELECTRONS, NEUTRONS, AND ALPHA PARTICLES 555 



ten times in relation to 7-ray ionization. No way has so far been 

 devised to accomplish this weighting fully except by analysis of the 

 observed ionization into the components due to 7 radiation on the one 

 hand and fast and slow neutron ionization on the other. With care 

 this may usually be accomplished by the use of at least two different 

 ionization chambers, the one of which has true tissue composition 

 and responds to all radiation proportionately, and the other having 

 no hydrogen or nitrogen content and therefore heavily weighting 7 

 ray as compared with the other forms of energy absorption. Inas- 

 much as hydrogen, which is present only to the extent of 10% (Table 

 VI) contributes over 90% of the neutron energy absorption in tissue, 

 it is clear that the neutron energy absorbed per gram will be ten times 

 greater in hydrogen than in tissue. Gamma-ray energy absorption 

 per gram is twice as great in hydrogen as in any other element. A 

 large ionization chamber containing hydrogen gas at high pressure 

 therefore automatically weights neutron ionization relative to 7-ray 

 ionization in the ratio of about five to one. Boron might be added 

 to make an appropriate slow neutron contribution. The experimental 

 separation of 7-ray and fast neutron effects was studied by Lea {95) 

 and by Aebersold and Anslow {91). 



Beta Radiation and Alpha Radiation from Radioactive Material 

 Uniformly Distributed in Tissue. If the concentration of radio- 

 active material in tissue is known and also the mean energy of the 

 jS particles emitted at each disintegration, it is obviously easy to cal- 

 culate the average |S-ray energy expended per unit mass of tissue in 

 which a radioactive element is uniformly incorporated, and if this 

 energy is divided by 84 ergs per gram we obtain the dose in equiva- 

 lent roentgens. The total dose resulting from complete decay of the 

 radioactive material has been given in a convenient form as follows 

 {55) : 



Dp = 88 Ep TC r.e.p. (25) 



= 79 Ep TC energy units 



where E^ is the mean energy in m.e.v. of the /3 rays emitted by this 

 source, T is the half-life in days, and C is the concentration of the iso- 

 tope in microcuries per gram 



Correspondingly, the initial dose rate is given by: 



dose rate = 2.54 E^C r.e.p./hour (26) 



= 2.29 EffC energy units/hour 



