179
AT norm ATno(max) ATdef
1/2 t2
tT12 tT1/2 /2
ATnorm(per avg)
A B
0.25 ----- -- ---- 0.3--
0.2 ATnorm(max 0.25 --
0.15
I I I ------0.2 --- --- -- -- - -
0o.-1 -- ATdef /
0.15 -- - -
0.050.05
0.1 ^ ^< 0.1--
-0.05 -
0.05
0.1 ATnorm(per avg) 0 -
0.15 I I I I II-0.05 I I----
0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8
Square Root of Time (sec1/2) Square Root of Time (sec1/2)
C D
Figure 6-60. Computation of ATdef from normalized temperature data. A) ATnorm for
idealized case. B) corresponding ATdef C) ATnorm for Defect A75,
Specimen A-2. D) corresponding ATdef
The procedure is illustrated for Defect A50 on Specimen A-2 in Figure 6-61. The
hatched area in the figure represents the average ATnorm on the perimeter of the area with
a range of +/- 20. At tl/2 = 4.2 (t = 18 sec), ATdef exceeds the upper boundary defined by
ATnorm(per avg) + 2c. This point corresponds to tT12
It is important to note that the extracted value for tT1/2 represents a "best-estimate".
For the defect described in Figure 6-61, it was determined that the signal for the defect
diverged from the surrounding noise at t = 18 sec. Close inspection of the area at t = 13
sec (five seconds before tT1/2) reveals a signal has developed above the implanted defect
(Figure 6-62A), but the magnitude is on the same scale as the surrounding noise. At t =