Math Review Worksheet
To solve for a distance use the following formula:
[latex]D _ { 2 } = \sqrt { \frac { I _ { 1 } x D _ { 1 } ^ { 2 } } { I _ { 2 } } }[/latex]
D = Distance I = Intensity in Röntgens
To solve for Intensity use the following formula:
[latex]I _ { 2 } = \frac { I _ { 1 } x D _ { 1 } ^ { 2 } } { D _ { 2 } ^ { 2 } }[/latex]
D = Distance I = Intensity in Röntgens
Iridium 192: 0.48 R/hr/ci @ 1M or 5.2 R/hr/ci @ 1’
Iridium 192 Half-life is 73.83 (74) Days
Cobalt 60: 1.30 R/hr/ci @ 1M or 14 R/hr/ci @ 1’
Cobalt 60 Half-life is 5.247 years
1 R = 1000 mr 1M = 3.28 ‘ = 39.37” 1” = 2.54 cm, 1’ = 30.48 cm
HVL Formula: Io = Original Intensity; Id = Desired intensity
1. We know that 1 ci of iridium 192 emits 5.2 R/hr @ 1ft. so a 2 ci source of IR 192 would emit how many R/hr @ 1ft?
2. We have 25 R/hr @ 12”, what is our intensity at 10 feet?
a. Does the difference in units matter? Y or N?
b. Write out the equation and Solve for our new intensity.
c. ANSWER:
3. We have 37 R/hr @ 3M, what is our intensity at 75 feet?
a. Are your units converted?
b. What’s the intensity in mr/hr?
a. ANSWER:
4. We know that 1 ci of iridium 192 emits 5.2 R/hr @ 1ft. So a 75 ci source of IR 192 would emit how many R/hr @ 1ft?
5. Using a 75 ci source of IR 192 at 12”, Calculate the distance (D2) to the “safe for public dosage.”
a. What is the Safe Public Dose?
b. Show your work.
c. Answer:
6. We have 199 mr/hr @72”, and our desired I2 is the safe to public radiation dosage.
a. What is the safe for public Radiation Dose?
b. How far do we need to be? Solve for (D2) in Feet.
7. We now have a 100 ci source of IR 192.
a. How many R/hr @1 ft? 520 R/hr
b. What is the “Caution: Radiation Area” working dosage?
c. Solve for D2 and assume I2 is the Caution dosage of:
8. Cobalt 60 emits 14 R/hr/ci @ 1ft.
a. How many R/hr is emitted at 1 ft. with a 100 ci source of Co 60? 1,400 R/hr
b. Solve for D2 and assume I2 is the public safe dosage of 2 mr/hr.
9. Cobalt 60 emits 14 R/hr/ci @ 1ft.
a. How many R/hr is emitted at 1 ft. with a 100 ci source of Co 60?
b. Solve for D2 and assume I2 is the “caution Radiation Work Area” dosage of 5mr/hr
10. We now have a 100 ci source of IR 192.
a. How many R/hr @1 ft?
b. Solve for D2 and assume I2 is the “caution Radiation Work Area” dosage of 5mr/hr.
11. Assuming a source has a ½ life of 20 years, how old would the source be in 3 half- lives?
a. If a radiographer has 60 mR at the surface of the exposure device, what would the reading be after 2 half- lives?
a. 15 mR
b. 40 mR
c. 80 mR
d. 10 mR
13. The use of 4 half-value layers will reduce the exposure by a factor of:
a. 4 times
b. 8 times
c. 16 times
d. 32 times
14. If a radiographer has 98 Ci of Ir-192, after 148 days how many Curies would be left?
a. 49 Ci
b. 22 Ci
c. 12 Ci
d. 24.5 Ci
15. A cobalt source has decayed from its original activity after 3 half-lives. Originally it was 88 Ci. Its current activity is:
a. 44 Ci
b. 22 Ci
c. 11 Ci
d. 8 Ci
16. A cobalt source of 73 Ci is exposed for a fu