Radiation Transducers 



The field is divided into two sections: transducers responding to 

 optical radiation (5-1) and transducers responding to ionizing 

 radiation (5-2). 



5-1. Optical Radiation Transducers 



Optical transducers comprise photoemissive systems (5-11), 

 photoconductive (5-12). photovoltaic (5-13), and thermal systems 

 (5-14). 



5-11. Photoemissive Transducers 



A photoemissive transducer, Fig. (5-1)1, contains in general a 

 metallic cathode C and an anode A in an evacuated envelope. Light 

 strikes the cathode and liberates elec- 

 trons. The electrons are attracted by 

 and move toward a positive anode and 

 thereby form an electric current. 



If a light quantum of the wavelength 

 X interacts with an electron bound in a 

 metal, the entire quantum energy A = 

 he/?, (h, Planck's constant, 6.62 x 10- 34 

 watt/sec 2 ; c, propagation velocity of 



light, 3 X 10 8 m/sec) will be converted into the kinetic energy of the 

 electron. 



The kinetic energy enables the electron to leave the metal surface 

 with an energy 



a =--*? 



233 



Fig. (5-1)1. Photoelectric cell 

 and basic circuit. 



