NAC459.572. Fluoroscopic X-ray systems: Barrier-rate limits.

     1. The exposure rate resulting from transmission through the primary protective barrier with the attenuation block in the useful beam, combined with radiation from the image intensifier, if provided, must not exceed 2 milliroentgens per hour at 10 centimeters from any accessible surface of the fluoroscopic imaging assembly beyond the plane of the image receptor for each roentgen per minute of entrance exposure rate.

     2. The exposure rate due to transmission through the primary protective barrier combined with radiation from the image intensifier must be determined by measurements averaged over an area of 100 square centimeters with no linear dimension greater than 20 centimeters.

     3. If the source is below the tabletop, the measurement must be made with the input surface of the fluoroscopic imaging assembly positioned 30 centimeters above the tabletop.

     4. If the source is above the tabletop and the source-image receptor distance is variable, the measurement must be made with the end of the beam-limiting device or spacer as close to the tabletop as it can be placed, but it must not be closer than 30 centimeters.

     5. The attenuation block must be positioned in useful beam 10 centimeters from the point of measurement of entrance exposure rate and between this point and the input surface of the fluoroscopic imaging assembly.

     [Bd. of Health, Radiation Control Reg. §§ 6.5.4-6.5.4.2.4, eff. 2-28-80]