Radiation Safety Series 5

Radiation Safety Series 5 Controlling Radiation Dose

Controlling Radiation Dose Complying with ALARA Time, Distance, Shielding Less time, less dose Greater distance, less dose More shielding, less dose

Dose Formula Intensity x Time = Distance I = Intensity (dose rate) T = Time D = Dose IxT=D Rate x Time = Distance

Time Problems While an iridium192 source is in the unshielded position during a radiograph exposure, the dose rate (I) at the control cable crank is 200 mR/hr. If you were to remain standing at the crank for the entire exposure , what would your dose be if the exposure was twelve minutes?

Time Problems Step 1: convert 12 minutes to hours 12 min =0.2hours 60 min hr

Step 2: use the formula D = I x T D = 200 mR/hr x 0.2 hours D = 40 mR

Time Problems If your exposure was 2 minutes ? 2 min =0.033hours 60 min hr

D = 200 mR/hr x 0.033 hours D = 6.6 mR

Time Problems If your exposure was 30 seconds? 30 sec 3600 sec

=0.0083hours hr

D = 200 mR/hr x 0.0083 hours D = 1.66 mR

Another Time Problem A Gamma radiographic team of two individuals must radiograph ten pipe girth welds at one location. Each weld requires three exposures. They have a 100-curie Iridium 192 source. During the travel during the travel of the source from the camera to the position in the collimator the radiographer measures a dose rate of 500 mR/hr at the crank. It takes five seconds to crank the source in or out. If the radiographer cranked the source what dose would the radiographer receive while radiographing the 10 welds?

Another Time Problem Step 1: convert 5 seconds to hours. There are 3600 seconds in 1 hour. 5 sec = 0.0014hours 3600hours

Step 2: use the formula I x T = D. D = 500 mR/hr x 0.0014 hours D = 0.7 mR per crank.

Another Time Problem