X-RAY TUBE 20: For a fixed anode x-ray tube operating under the following condit

Question

X-RAY TUBE 20: For a fixed anode x-ray tube operating under the following conditions: Tube current, Ia = 0.6 mA Exposure time, t = 0.5 s Tube voltage, V= 100 kVp (assume the HV generator delivers close to DC)

a) Calculate the total charge and energy deposited at the anode

b) Calculate the maximum velocity with which an electron interacts with the anode material

c) Estimate the minimum wavelength of an X-ray photon emitted by the tube

X-RAY TUBE 21: In a pin-hole set-up, a lead plate with a 0.8 mm diameter hole is placed at a distance of 20 cm from the anode target, and 50 cm from the X-ray film. For a given target length of 0.2 cm, calculate the size of the hole image for anode angles of 1) 10°; and 2) 20°. Using your results, explain the effect of anode angle on spatial resolution. Hint: Sketch the experimental set-up and use similar triangles to solve this problem.

X-RAY TUBE 22: You are using an x-ray tube with the following tube settings and parameters: Tube voltage: 110 kVp Tube current: 250 mA Exposure time: 0.9 s Anode angle: 15° Anode diameter: 40 mm Anode heat-storage capacity: 300 kHU Anode material specific heat load: 50 W/cm2

a) If the visible focal spot area = 0.01 cm2 , determine the heat load to the anode assuming

i) a fixed anode

ii) a rotating anode at a rotation speed of 50 rps

iii) a rotating anode at a rotation speed of 150 rps

b) Of the three conditions in a), which is the best for making the required exposure? Explain.

c) For the condition selected in b) calculate the total number of exposures permissible for assuming that the high-voltage generator delivers i) Single-phase, full-wave, sinusoidally-varying output ii) close to DC output (i.e., a three-phase full-wave power supply) X-

RAY TUBE 23: For a mammographic examination, in which low tube voltage settings (40-50 kVp) are used, for a given visible focal spot size, is it better to use

a) an anode angle of 10° or 15°?

b) a single-phase or a three-phase power supply?

c) Would the answers to a) and b) change for a chest X-ray examination which requires a higher tube voltage setting (90-140 kVp)? Homework 1 is due in lab during the week of Sep 14. Submit to Lab TA at the beginning of your lab session.

Explanation / Answer

20

a)

Tube current, Ia = 0.6 mA

Exposure time, t = 0.5 s

Tube voltage, V= 100 kV

Energy = V Ia t = 105 * 0.6* 10-3 * 0.5 = 3 J

Charge = I t = 3*10-4 C

b)

E = eV = 0.5 m v2

=> v = 1.874*108 m /s ( Note: this speed is close to speed of light, hence relativity will come into picture, but this value does not take relativity into account)

C)

Minimum wavelength= h/mv = 3.88*10-12 m

(NOTE: Please post different questions separately. the above solution is question 20 part a,b,c)

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