RADIOACTIVITY METHODS 



1005 



Scintillation counters'^ are a new development in the field of nuclear 

 instrumentation. Various organic and inorganic crystals emit visible and 

 ultraviolet light when traversed by ionizing radiation. The proper crystals 

 are transparent to their own radiation so that the light flash from each 

 ionizing event can be picked up by an electron-multiplier phototube. The 

 pulses from the phototube are then amplified and recorded. 



Various investigators have used anthracene, naphthalene (moth flakes), 

 scheelite, alkali halides, and other crystals in their experiments. The princi- 

 pal advantage of the scintillation counter is its high y efficiency. Almost 



LUCITE INSULATOR 



EXHAUST 



CENTER WIRE 



Fig. 622. — Sketch of methane-flow 

 proportional counter with circular center 

 wire. (Courtesy of Nuclear Measure- 

 ments Corporation.) 



Fig. 623. — Electronic equipment (amplifier and scale 

 of 512 scaler) for proportional center wire counter. 

 (Courtesy of Nuclear Measurements Corporation.) 



every y passing through a relatively dense large crystal will lose a frac- 

 tion of energy sufficient to produce a countable flash. The resulting 

 pulses are much shorter than pulses from a G-M tube, and fast amplifiers 

 with very high resolution can be used. 



Photographic nuclear emulsions can be very useful in detecting ionizing 

 radiation, particularly a particles. | The dense ionization of the a's produces 

 sharp tracks that are clearly visible under the microscope. The method is 

 particularly well adapted to the study of the a radioactivity of small grains 

 and the detailed examination of activity in polished sections. 



Auxiliary Equipment. — The scaling circuit is an electronic device for 

 counting the random pulses from radiation detectors. The pulses frequently 



t H. Kallman, "Quantitative Measurements with Scintillation Counters," Phys. Rev. 75, 623-6 

 (1949). 



P. R. Bell, "The Use of Anthracene as a Scintillation Counter," Phys. Rev. 73, 1405-6 (1948). 

 See also .4ECD 1854 and 1889, Oak Ridge Natl. Lab. (1948). 



R. J. Moon, "Inorganic Crystals for the Detection of High Energy Particles and Quanta," 

 Phys. Rev. 73, 1210 (1948). 



t H. Yagoda, "Radioactive Measurements with Nuclear Emulsions," John Wiley and Son, New 

 York (1949). 



