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13. A Build-up Model for Thickness Gauging of Steel Plates Based on Gamma-ray Transmission
Yoshiyuki Shirakawa
Keywords: build-up effect, thickness gauging, steel plate, gamma-ray transmission, linear attenuation coefficient
A non-linear build-up model for thickness gauging of steel plate, which is based on a gamma-ray transmission technique, has been proposed. Its performance was evaluated by experiments using a real 137Cs thickness gauge installed on a heavy plate mill used in steel manufacturing.
A conventional gamma-ray thickness gauge employs many linear measurement models as given by eq. (1),
I=I0exp(-
Xi) (1)
where I0 and I are the number of incident gamma-rays and the number of transmitted ones respectively, (cm-1) is a linear attenuation coefficient of measured objects, in this case steel plates, and Xi (cm) is thickness in the i-th measuring range. The models deal with only a small measurement range each and the same number of standard steel plates is needed for model parameter calibration.
The proposed model with a variable linear attenuation coefficient (cm-1) is shown in eq. (2),
I=I0exp(-(X)X), (X)=(0 /
)[exp(-
X)+(-1)] (2)
where0 is the ideal linear attenuation coefficient obtained under the condition of X
0, and and are positive constants given by previous experiments, includes build-up effects in (X) . Although it is a little more complicated to solve X in eq. (2) than in eq. (1), the new model has advantages that it can cover a much wider range of measurements and it requires a fewer calibration plates.
It was shown that the values calculated with the non-linear model of eq. (2) were in good agreement with experimental data obtained by the gamma-ray thickness gauge in the range of 0-10cm thickness. The relative accuracy of thickness measurements was within ± 0.05% and the absolute accuracy was within ± 2 m in the thickness range of 0-10cm. Hence the new model has a potential for real use in current thickness gauging and meets requirements of simplicity and easy handling.
Publications:
1)Shirakawa Y., Horikoshi K. and Amano H.: SICE,35,5,693-695,1999.
2)Shirakawa Y., Horikoshi K. and Amano H.:IMEKO-15th,TC-14,165-170,1999.
