T.O. 33B-1-1 6-154 Table 6-28.  Peak Voltage (kVp) TABLE.  HALF-VALUE AND TENTH-VALUE LAYERS |Approximate values obtained at high attenuation for the indicated peak voltage at, Peak Voltage (kVp) Attenuation Material Peak Voltage (kVp) Lead (mm) Concrete (in) Steel (in) HVL TVL HVL TVL HVL TVL 50 0.05 0.16 0.17 0.6 70 0.15 0.5 0.33 1.1 100 0.24 0.8 0.6 2.0 125 0.27 0.9 0.8 2.6 150 0.29 0.95 0.88 2.9 200 0.48 1.6 1.0 3.3 250 0.9 3.0 1.1 3.7 300 1.4 4.6 123 4.1 400 2.2 7.3 1.3 4.3 500 3.6 11.9 1.4 4.6 1000 7.9 26 1.75 5.8 2000 12.7 42 2.5 8.3 3000 14.7 48.5 2.9 9.5 4000 16.5 54.8 3.6 12.0 1.08 3.6 6000 17.0 56.6 4.1 13.7 1.2 4.0 10000 16.5 55.0 4.6 15.3 Cesium-137 6.5 21.6 6.2 .064 2.1 Cobalt-60 12 40 8.1 0.82 2.7 Radium 16.6 55 2.7 9.2 0.88 2.9 6.9.20.1 Quality of Protective Material. All shielding materials shall be of assured quality, uniformity and permanency 6.9.20.2 Lead Barriers. a.     Lead  barriers  shall  be  mounted  in  such  a  manner  that  they  will  not  cold-flow  because  of  their  own weight and shall be protected against mechanical damage. b.    Lead sheets at joints should be in contact with a lap of at least one-half inch, or twice the thickness of the sheet, whichever is the greater. c.     Welded or burned lead seams are permissible provided the lead equivalent of the seams is not less than the minimum requirement. 6.9.20.3 Joints Between Different Materials or Structures. a.     Joints between different kinds of protective materials shall be constructed so that the overall protection of the barrier is not impaired. b.    Joints at the floor and ceiling shall be constructed so that the overall protection is not impaired.