Radiation Calculations: Decay, Distance, Shielding practice questions for the ASP exam
ASP11 Domain 1: Mathematical Calculations (1.x Ionizing radiation calculations). 3 free questions below. Every answer quotes and links the formula source it rests on.
A radiography source reads 60 mR/hr at 2 ft (a point source, no shielding). The site's procedure requires a barricade where the rate is no more than 2 mR/hr. Using the inverse square law, about how far from the source should the barricade be?
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Answer: A. 11.0 ft
I2 = I1 (d1/d2)², so d2 = d1 x √(I1/I2) = 2 x √(60/2) = 11.0 ft. Scaling distance linearly with intensity (60.0 ft) overstates the distance needed.
“Estimating Attenuation in Air Using Inverse Square Law I 2 = I 1 [ d 1 / d 2 ] 2”
A radiography source reads 200 mR/hr at 3 ft (a point source, no shielding). The site's procedure requires a barricade where the rate is no more than 2 mR/hr. Using the inverse square law, about how far from the source should the barricade be?
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Answer: C. 30.0 ft
I2 = I1 (d1/d2)², so d2 = d1 x √(I1/I2) = 3 x √(200/2) = 30.0 ft. Scaling distance linearly with intensity (300.0 ft) overstates the distance needed.
“Estimating Attenuation in Air Using Inverse Square Law I 2 = I 1 [ d 1 / d 2 ] 2”
A radiography source reads 150 mR/hr at 3 ft (a point source, no shielding). The site's procedure requires a barricade where the rate is no more than 2 mR/hr. Using the inverse square law, about how far from the source should the barricade be?
Show answer and source
Answer: B. 26.0 ft
I2 = I1 (d1/d2)², so d2 = d1 x √(I1/I2) = 3 x √(150/2) = 26.0 ft. Scaling distance linearly with intensity (225.0 ft) overstates the distance needed.
“Estimating Attenuation in Air Using Inverse Square Law I 2 = I 1 [ d 1 / d 2 ] 2”
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