-DIRECT CONNECTION 



SCANNER 



SYSTEM SEQUENCING, 



MONITORING, AND 



TELEMETRY 



ADJACENT TO SPECIMEN 

 WORK SITE 



DATA ACQUISITION 



AND SYSTEM 



CONTROL 



WORK SITE OR REMOTE 



HIGH SPEED 

 TELEMETRY LINK 



■DIRECT CONNECTION OR 

 COMPUTER MEDIA 



DATA CONDITIONING, 



RECONSTRUCTION, 



AND DISPLAY 



Figure 5. Functional block, diagram of Computerized Axial Tomography 

 System. 



The inspection criteria for the scanner design was established based 

 on the maximum diameter of wood pilings (18 inches), minimum internal 

 flaw size desired to be detected (12.7 mm), capabilities of the present 

 state-of-the-art detectors, and use of Iridium as the isotope source. 

 The inspection criteria for wood under water are as follows: (1) the 

 density resolution (Ap) , 0.5%, and (2) spatial (width) resolution 6 mm 

 < Aw < 12 mm. 



The scan time depends on the specimen thickness (w) , spatial resolu- 

 tion (Aw) and density resolution (Ap) . With a 18-inch wood piling and 

 an Iridium source, the minimum scan times in minutes are based on de- 

 tecting internal and external damage. Since damage to wood structures 

 is primarily due to biological attack, the detection criteria are based 

 on the size of the organism. The average size of shipworms (these cause 

 interior damage) would equate in tomographic parameters to a spatial 

 resolution (Aw) of 1/2 inch (12.7 mm) as the minimum spatial require- 

 ment. To detect the damage caused by the Woodgribble (most severe in 

 terms of small spatial resolutions) , a 1/8-inch (3-mm) spatial resolu- 

 tion would be necessary. Since the damage caused by the Woodgribble is 

 exterior, the spatial resolution was eased. 



14 



