The Design of Diagnostic Medical Facilities where ... - ResearchGate

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χ = ln
αγ
B
−γ
1+
+
β
α
β
α
Equation 5.6
where α, β and γ are the fitting parameters. Values for α, β and γ have been published for a selection of
materials at a range of diagnostic energies. Coefficients for primary transmission of lead and concrete, and
the coefficients for secondary radiation between 100 – 150 kVp are reproduced in Table 5.7 (BIR, 2000). For
calculations involving secondary radiation at energies less than 100 kVp, primary radiation data can be used
as it has been shown that the differences are negligible (BIR, 2000).
Table 5.7: Coefficients for generating primary and secondary transmission curves for lead and
concrete (based on BIR, 2000)
Material kVp α β γ
Lead 30 38.80 178 0.347
50 8.801 27.28 0.296
70 5.369 23.49 0.588
90 3.067 18.83 0.773
100 (primary) 2.500 15.28 0.756
125 (primary) 2.219 7.923 0.539
100 (secondary) 2.507 15.33 0.912
125 (secondary) 2.233 7.89 0.730
150 (secondary) 1.791 5.48 0.568
Concrete 30 0.3173 1.698 0.359
50 0.0903 0.1712 0.232
70 0.0509 0.1696 0.385
90 0.0423 0.1137 0.469
100 (primary) 0.0393 0.0857 0.427
125 (primary) 0.0352 0.0711 0.697
100 (secondary) 0.0395 0.084 0.519
125 (secondary) 0.0351 0.066 0.783
150 (secondary) 0.0324 0.078 1.566
The thickness of material can also be determined by using the limiting half value layer (HVL) for a given
material at a particular kVp. This approach will result in a conservative shielding design as the limiting HVL
model assumes a highly penetrating beam (BIR, 2000).
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The Design of Diagnostic Medical Facilities where Ionising Radiation is used