Question

Concerning the construction of direct conversion detectors: 

a. The photo conductor produces electrical charge when irradiated 

b. It is still dependent on a silicon-based transistor 

c. A potential difference is applied across the photo conductor to increase the charge formed per X-ray photon 

d. The signal for image formation is carried by the negative charge (electrons)

e. It is designed to be compatible with more than one radio graphic machine 

Answer 1

a. True. The commonly used photo conductor is amorphous selenium. 

b. True. The photo conductor is usually bound to the amorphous silicon transistor array.

c. False. Electrodes are placed across the photo conductor, which draws the released electrons and positively charged holes to the anode and cathode, respectively. The potential does not affect the absorption of the X-ray or the charge formed per photon. 

d. False. It is the positively charged holes that accumulate in the storage capacitors associated with each pixel. It is this charge that then forms the latent image by being digitized and transferred to the computer system. 

e. False. This is one of the main disadvantages.