BIOLOGICAL EFFECTS OF RADIATIONS 709 



is intense but most of them do not penetrate deeply into tissue. The 

 gamma rays are similar to high voltage roentgen radiation and 

 their biological action is very much the same. There is a difference 

 in their application in that the radium is usually placed close to the 

 biological material and then effects are more localized than that of 

 roentgen radiation. 



Effects of Other Radiations 



The ionization produced by neutrons in tissue is initiated in a 

 manner different from that of the roentgen and gamma radiations 

 already mentioned. The neutron ionization is much more localized 

 and intense. The neutron releases its energy by knocking the hy- 

 drogen nucleus, the proton, free from its outer electron. This recoil 

 proton is so large that it comes in contact with many atoms (thus 

 producing ions) within a short range before it dissipates its energy, 

 picks up an electron and becomes an ordinary hydrogen atom again. 

 Neutrons are more readily absorbed in light substances rich in hy- 

 drogen (as biological tissues and water), than in denser substances 

 such as iron or lead. In terms of ionization in air, the neutrons 

 appear to be from five to fifteen times more effective than roentgen 

 radiation in killing cells. Qualitatively, the therapeutic effects of 

 the fast neutrons have so far been similar to those of roentgen 

 radiation. 



Radioactive substances have proved to be valuable as tracers in 

 following atoms through metabolic processes in the body. Eadio- 

 active iodine, for example, can be fed and within a short time the 

 region of the thyroid will be giving off radiation that can be de- 

 tected by the Geiger counter (sensitive ionization chamber). Radio- 

 active phosphorus shows promise of becoming of value in the treat- 

 ment of diseases related to excess bone marrow development. It 

 appears that phosphorus is concentrated in malignant bone marrow 

 cells and thus the concentration of radioactivity becomes great 

 enough to destroy them. 



Cosmic rays abound in the atmosphere and penetrate to depths 

 of even the heavier materials. Apparently not enough of the radi- 

 ation is absorbed by biological material to be effective. However, 

 from time to time one hears of the theory that natural mutations 

 may be the result of cosmic rays affecting the chromosomes of the 

 germ cells. 



