13-5] NUCLEAR RADIATION 693 



shields. Attenuation of neutrons differs from that of gamma rays in that 

 neutrons are slowed down most effectively by using light materials for 

 shielding. Water is a commonly used substance to attenuate neutrons. The 

 actual amount of destruction or deterioration of either the mechanical or 

 electrical component parts of a system depends on the type of radiation and 

 distribution of energy in the immediate area. 



Electrical materials are affected in many ways upon being subjected to a 

 nuclear radiation field. Studies indicate that components like transistors, 

 condensers, rectifiers, and semiconductors in general are unstable at certain 

 levels of radiation. Moreover, serious trouble can occur in tubes because 

 the irradiation process deteriorates the various types of tube seals, thus 

 allowing air into the tube. Various changes in the characteristics of oil 

 subjected to nuclear radiation (for example, changes in the viscosity) can 

 result in- the breakdown of oil-filled capacitors. Resistors may malfunction 

 as an effect of nuclear radiation acting on the insulation used on the cover. 



Insulation materials used for most electrical components are not able to 

 resist nuclear radiation. The fatigue life or wear rate of some electrical 

 components appears to be accelerated in a nuclear or ionized atmosphere. 

 Relay and switch contacts are examples of this type of effect. Changes in 

 electrical resistivity have been demonstrated in electrical insulators. 



Structural materials used in the fabrication of electronic equipment are 

 affected to varying degrees when subjected to a nuclear radiation environ- 

 ment. For example, the aluminum alloys indicate an increase in the tensile, 

 yield, and shear strengths and a decrease in the percentage of elongation, 

 resulting in a reduction in ductility. This leads to an increase in the notch 

 sensitivity or stress concentration effect and a decrease in the ability of the 

 material to resist an impact loading. The corrosion resistance of material is 

 improved, when subjected to certain levels of radiation intensity, because 

 of the chemical effects on the surface of the material. 



The elasticity of materials similar to rubber is reduced. Fluids used 

 in hydraulic systems, lubricants of different types, and fuel for aircraft 

 power plants all exhibit unfavorable changes in their characteristics when 

 subjected to nuclear radiation. Plastics tend to change in color and become 

 increasingly brittle with increase of radiation intensity. 



To produce an airborne radar system capable of satisfactory operation in 

 a nuclear radiation environment requires the maximum of effort in the 

 study of basic materials, electrical component fabrication techniques, and 

 shielding methods. Close coordination between the electronic equipment 

 designer and airframe designer is an absolute necessity in achieving the 

 optimum design. 



It is not possible to shield the nuclear reactor completely and thus 

 eliminate this environment external to the shield. For ground-installed 

 nuclear power plants, the large bulk or weight and surface area necessary 



