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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard is formulated in accordance with Law of the People's Republic of China on Prevention and Control of Occupational Diseases.
Radiation shielding specifications for room of industrial X-ray radiography
1 Scope
This standard specifies the radiation shielding specifications for rooms of industrial X-ray radiography.
This standard applies to detection rooms for industrial X-ray radiography devices of 500 kV and below.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
room of X-ray detection
irradiation room for special X-ray radiography devices, used for X-ray radiography and having a shielding structure to ensure radiation safety in outdoor place
2.2
reference point
determined position beyond the detection room, which plays a decisive role in shielding structure of detection room, designed for detection room radiation shielding and dose estimation. It is usually away from the surface of detection room 30 cm where people may be exposed to the greatest dose. A position having some distance away from the detection room and that with high occupancy factors for members of the public and may be exposed to large doses shall also be considered as reference point
2.3
shielding transmission factor
ratio of radiation doses of a reference point with and without shielding between this reference point and a radiation source
3 Shielding requirements of detection room
3.1 Dose reference control level of radiation shielding for detection room
3.1.1 The ambient dose equivalent rate of the detection room wall and entrance door (hereinafter referred to as “dose rate”) and the weekly ambient dose equivalent rate (hereinafter referred to as “weekly dose”) shall meet the following requirements:
a) Weekly dose reference control level (HC) and derived dose rate reference control level (H ?c,d):
1) Weekly dose reference control level of personnel at the reference point HC is as follows:
Vocational staff: H ?c ≤ 100 μ Sv/week;
Public: Hc ≤ 5 μSv/week.
2) The derived dose rate reference control level H ?c,d (μSv/h) of corresponding Hc is calculated according to Equation (1):
H ?c,d = Hc/(t·U·T) (1)
where,
Hc——the weekly dose reference control level, μSv/week;
U——the use factor of the radiography device irradiating to the direction of reference point;
T——the occupancy factor for the personnel lingering at the corresponding reference point.
t——the weekly therapy irradiation time of the radiography device, in h/week;
t is calculated according to Equation (2):
t=W/(60?Ι) (2)
where,
W——the weekly working load of X-ray radiography (average weekly X-ray radiographic exposure "mA·min" value), mA·min/week;
60——the conversion factor between hours and minutes;
I——the maximum common tube current of the X-ray radiography device at the highest tube voltage, mA.
b) Maximum dose rate reference control level H ?c,max of reference point:
H ?c,max = 2.5 μSv/h
c) Reference control level H ?c for dose rate of reference point
H ?c is the smaller value between the above H ?c,d in a) and H ?c,max in b) .
3.1.2 The dose rate reference control level at the top of the detection room shall meet the following requirements:
a) If the existing or proposed building above the detection room or the adjacent building beside it is in the solid angle area from the radiation source point to the edge of the inside surface of the detection room roof, for 30 cm away from the outer surface of the top of the flaw detection chamber as well as a personnel residence in a high-rise building within the solid angle area, the dose reference control level for radiation shielding is the same as 3.1.1.
b) In addition to the conditions in 3.1.2 a), the following circumstances shall be considered:
1) The radiation passing through the top of the detection room and the exposure to the public near the ground outside the detection room by scattered radiation generated by the action of air above the roof. The sum of the dose rate of the radiation and the transmitted radiation passing through the wall of the detection room at the corresponding reference point shall be controlled according to the dose rate reference control level H ?c(μSv/h) in 3.1.1 c).
2) For the top of the detection room that is unnecessary for staff to reach, the dose rate reference control level at the location of 30 cm from the outer surface of the top of the detection room is taken as 100 μSv/h.
3.2 Radiation to be shielded
3.2.1 The whole end face of the corresponding useful beam is shielded by the useful beam without considering the scattered radiation entering the useful beam area.
3.2.2 Taking 90° scattered radiation which incidents the workpiece with 0° incident angle.
3.2.3 If the combined effect of leakage radiation and scattered radiation may exist, the leakage radiation and each scattered radiation are usually estimated separately; if their shielding thickness is different by tenth-value layer (TVL) or larger, the thicker shield is adopted; if the difference is less than one TVL, a half-value layer (HVL) of thickness is added to the thicker shield.
3.3 Other requirements
3.3.1 Generally, the detection room shall be equipped with a staff door and a separate workpiece door. For a small-scale workpiece detection room where the radiography device is manually transferred, only the staff door may be provided, and this staff door shall be set as a maze entrance.
3.3.2 The control room for the radiography device shall be placed outside the detection room, and the staff door shall avoid the direction irradiated by useful beam.
3.3.3 For shielding design, the shielding of gaps, pipe holes and weak links shall be considered.
3.3.4 If the detection room uses multiple X-ray radiography devices, X-ray shielding shall be designed according to the highest tube voltage and the maximum common tube current at this corresponding tube voltage.
3.3.5 The structure, construction cost and occupied space of the detection room shall be considered. Commonly used materials are concrete, lead and steel plate.
4 Estimation method of radiation shielding for detection room
4.1 Restriction of useful beam
The shielding estimation method of useful beam is as follows:
a) If the reference point reaches the dose rate reference control level H ?c, the shielding transmission factor B required for shielding design is calculated by Equation (3), and then the corresponding thickness X of shielding materials is found out by the curve of Annex B.1.
B=(H ?_c?R^2)/(Ι?H_0 ) (3)
where,
H ?c——according to the determined dose rate reference control level in 3.1, μSv/h;
R——the distance from the radiation source point (target point) to the reference point, m;
I——the maximum common tube current of X-ray radiography device at the highest tube voltage, mA;
H0——the output 1 m away from the radiation source (target point), μSv·m2/(mA·h), the value in mSvvm2/(mA·min) multiples by 6×104. See Table B.1 in the Annex B.
b) At a given thickness X of shielding materials, the corresponding shielding transmission factor B is found out by the curve in Annex B.1. The dose rate of reference point H ?(μSv/h) is calculated according to Equation (4):
H ?=(I?H_0?B)/(Ι?H_0 ) (4)
where,
I——the maximum common tube current of X-ray radiography device at the highest tube voltage, mA;
H0——the output 1 m away from the radiation source (target point), μSv·m2/(mA·h), the value in mSv·m2/(mA·min) multiples by 6×104. See Table B.1 in Annex B.
B——the shielding transmission factor;
R——the distance from the radiation source point (target point) to the reference point, m;
4.2 Leakage radiation and scattered radiation shielding
4.2.1 The corresponding relationship between the thickness X of shielding materials and the shielding transmission factor B.
The mutual calculation for the thickness X of shielding materials and the shielding transmission factor B is as follows:
a) For a given thickness X of shielding materials, the corresponding radiation shielding transmission factor B is calculated according to Equation (5):
B=10-X/TVL (5)
where,
X——the thickness of shielding materials, take the same unit with TVL;
TVL——see Table B.2 in Annex B.
b) For the estimated shielding transmission factor B, the required thickness X of shielding materials is calculated according to Equation (6):
X =-TVL?lgB (6)
where,
TVL——see Table B.2 in Annex B.
B——the required shielding transmission factor if reaching the dose rate reference control level H ?c.
4.2.2 Leakage radiation shielding
Leakage radiation shielding shall be calculated by the following method:
a) If the reference point reaches the dose rate reference control level H ?c, the shielding transmission factor B required for shielding design is calculated by Equation (7), and then the required thickness X of shielding materials is found out by the curve of Annex B.1.
Foreword iii
1 Scope
2 Terms and definitions
3 Shielding requirements of detection room
3.1 Dose reference control level of radiation shielding for detection room
3.2 Radiation to be shielded
3.3 Other requirements
4 Estimation method of radiation shielding for detection room
4.1 Restriction of useful beam
4.2 Leakage radiation and scattered radiation shielding
5 Shielding thickness tables of detection room under typical conditions
5.1 Typical conditions
5.2 Tables of typical shielding thickness for detection room
5.3 Applications of typical shielding thickness tables
Annex A (Informative) Occupancy factor
Annex B (Informative) Typical parameters for radiation shielding estimation
Annex C (Informative) Example for shielding estimation of room of X-ray detection
Bibliography
