GBZ/T 250-2014Radiation shielding specification for room of industrial X-ray radiography (English PDF)

3.2 Radiation needed Shielding

3.2.1 The entire wall surface of the corresponding primary radiation shall adopt the primary radiation shielding, AND it is not needed to consider the scattered radiation entering into the primary radiation region.

3.2.2 As for the scattered radiation, CONSIDER the 90° scattered radiation which is incident into the detected work piece at 0°.

3.2.3 When there is a possibility of a combined effect of leakage radiation and scattered radiation, generally respectively ESTIMATE the leakage radiation and each scattered radiation; when the difference between their shielding thicknesses is equal to or more than one tenth value layer (TVL) thickness, SELECT the thicker shielding; when the difference is less than one tenth value layer (TVL), then at the thicker shielding, ADD a half value layer (HVL).

3.3 Other requirements

3.3.1 The detection room shall generally be provided with personnel doors and separate work-piece doors. As for the small work piece detection room wherein detection can be through manual handling, it can only provide the personnel door. AND the personnel door for the detection room shall adopt the labyrinth type.

3.3.2 The control room of the detection device shall be placed outside the detection room, AND the control room and personnel door shall avoid the direction of irradiation from primary radiation.

3.3.3 In the shielding design, it shall consider the shielding for the gap, pipe hole and other weak links.

3.3.4 When the detection room uses multiple X-ray radiography devices, DESIGN the shielding based on the maximum tube voltage and the normally used maximum tube current under such tube voltage.

3.3.5 It shall consider the detection room structure, building cost, and space

covered; AND the commonly used material is concrete, lead, and steel plate, etc.

Ro - The distance from the radiation source point (target) to the work piece under detection, in meters (m);

I - The commonly used maximum tube current of X-ray radiography device at the maximum tube voltage, in milliamps (mA);

Ho - The output at the location 1 m away from the radiation source point (target), µSv - m2/(mA - h), USE the value in the unit of mSv - m2/(mA - min) to multiple by 6 x 104; SEE Table B.1 of Appendix B.

F - The radiation field area at Ro, in square meters (m2);

alpha - Scattering factor, which is the ratio of the scattered radiation dose rate of the incident radiation onto the location 1 m away from it by the scatterer of 1m2 unit area to the incident radiation dose rate on this unit area. alpha is related to the scattering material; if the alpha value of the corresponding material does not obtained, USE the alpha value of water scatterer for conservative estimation; SEE B.4 of Appendix B;

c) When the shielding material thickness X is given, as for the corresponding shielding transmission factor B, in accordance with Table 2 and the corresponding values in Table B.1 of Appendix B, DETERMINE the TVL of 90° scattered radiation, then USE the equation (5) for calculation. The scattering dose rate for the reference point is calculated in accordance with the equation (10).

Where.

I - The commonly used maximum tube current of X-ray radiography device at the maximum tube voltage, in milliamps (mA);

Ho - The output at the location 1 m away from the radiation source point (target), µSv - m2/(mA - h), USE the value in the unit of mSv - m2/(mA - min) to multiple by 6 x 104; SEE Table B.1 of Appendix B.

B - Shielding transmission factor;

F - The radiation field area at Ro, in square meters (m2);

alpha - Scattering factor, which is the ratio of the scattered radiation dose rate of the incident radiation onto the location 1 m away from it by the scatterer of 1m2 unit area to the incident radiation dose rate on this unit that is, the required shielding wall thickness of the detection room is more than that of the sidewalk; in accordance with the dose rate requirements f the office building, ESTIMATE the final shielding thickness.

C.1.2.2 Examples of north wall (primary radiation) shielding estimation

a) CONDUCT estimation in accordance with the methods of 4.1. from Table B.1, the primary radiation output of the 300 kV tube voltage under 3 mm copper filtering conditions is 11.3 mGy-m2/(mA-min).

CALCULATE in accordance with the equation (3).

From the lead transmission curve of Figure B.1, the required lead thickness is 22.4 mm. It can also calculate the required concrete thickness is 560 mm.

b) ESTIMATE using the typical data sheet method. from Table 4, it is found that lead required at 2m and 3m is 23 mm and 21 mm respectively.

Through the interpolation, the lead shielding thickness at 2.3 m is 22.4 mm. It can also calculate the required concrete thickness which is 560 mm.

C.1.2.3 Example of west wall (leakage radiation and scattered radiation combination) shielding estimation.

a) ESTIMATE in accordance with the methods in 4.2.

1) Leakage radiation.

From Table 1, the leakage dose rate of 300 kV X-ray at 1 m from the target is 5 × 103 µSv/h. From Table C.1, is 1.2 µSv/h. CALCULATE in accordance with the equation (7).

From the Table B.2 of Appendix B, the tenth value layer of 300 kV X-ray in lead is 5.7 mm, and then USE the equation (6) to calculate the required lead thickness.

2) Scattered radiation.

References

[1] International Commission on Radiological Protection. Protection against ionising radiation from external sources used in medicine. ICRP Report 33.

Oxford. Pergamon Press, 1982.

[2] National Council on Radiation Protection and Measurements. Structural Shielding and Evaluation for Medical Use of X-Rays and Gamma-Rays of Energies Up To 10 MeV, NCRP Report 49, NCRP, Bethesda, MD, 1976.

[3] National Council on Radiation Protection and Measurements. Structural Shielding Design for Medical X-Ray Imaging Facilities, NCRP Report 147, NCRP, Bethesda, MD, 2004.

[4] American National Standards Institute, Inc. For General Radiation Safety-Installations Using Non-Medical X-Ray and Sealed Gamma-Ray Sources, Energies Up to 10 MeV, ANSI/HPS N43.3, ANSI, 2008.

[5] HMSO. Handbook of radiological protection, part 1. data. London. HMSO, 1971.