PROBLEMS 



1-1. A peak voltage of 80 kv is applied to an x-ray tube. What is the shortest 

 wavelength emitted? If a tungsten target is used will the characteristic frequencies 

 of tungsten be emitted? 



Ans. 0.155 A. 

 1-2. What is the longest x-ray wavelength that can penetrate the glass housing 

 of a Coolidge x-ray tube? 



1-3. Compute the value of A in Richardson's equation if the electron emission 

 is 4.2 milhamp/cm 2 of tungsten-filament surface when heated to 2000° K. 



Ans. 60.2 amp/cm 2 /degree 2 . 

 1-4. The work function of tungsten is 4.52 volts. How many ergs are expended 

 in removing an electron from a tungsten surface? 



Ans. 6.8 X 10~ 12 erg. 

 1-5. What minimum kilovoltage must be used to obtain the shortest wavelength 

 in the K series from an x-ray tube with a tungsten target? (X = 0.1794 A.) 



Ans. 69.0 kv. 

 1-6. A rock salt reflecting crystal is used in a Bragg x-ray spectrometer. An 

 intense reflection is observed to lie 7° 30' on either side of the central image. What 

 is the wavelength of the x-ray beam forming this image? 



Ans. 0.73 A. 

 1-7. In surface x-ray doses the incident intensity varies inversely as the square 

 of the skin-to-target distance. What change in time is required to give the same skin 

 dose if the skin-to-target distance is increased from 50 to 80 cm? 



Ans. 2.56. 

 1-8. Find the difference in the doses delivered at 10-cm tissue depth when the 

 x-ray tube is changed from 50 to 80 cm focal-skin distances. 



Ans. 79/70. 

 1-9. An automobile cost $1000. It depreciates 20 per cent in value per year. 

 What is the value at the end of the fifth year? 



Ans. $328. 

 1-10. An automobile costing $1500 depreciated continuously at a yearly per- 

 centage rate of 0.30. What was its value at the end of 8 years? 



Ans. $136. 

 I— 11. A sample of glass absorbed 2 per cent of the radiant energy passing through 

 it. How much energy will come out of a layer made up of 12 such samples? 



Ans. 78.8 per cent. 



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1-12. A parallel beam of x-rays of wavelength 0.080 A entered an ionization 

 chamber and its intensity was observed to be 100 units. Calculate the intensities 

 when 1 .0-mm sheets of aluminum, copper, and lead are in turn introduced in the beam. 

 Their densities are 2.70, 8.93, and 11.37 grams/cc respectively. What thickness will 

 reduce the intensity to half value? 



1-13. How does the penetration in tissue for x-rays of wavelength 0.15 A com- 



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pare with those of 0.25 A? 



1-14. The intensity of an unfiltered beam of x-rays, measured by an ionization 



355 



