1. RADIATION LAB TIME - DISTANCE - SHIELDING
Health Physics Society -
Power Reactor Section
Radiation Science Education

2. Time
Decrease the amount of time you spend near the source of radiation, and decrease the amount of radiation exposure you receive.
If you spend a lot of time on the beach, ultimately you get a sunburn. By reducing the amount of time you spend on the beach, you can avoid a sunburn.

3. Time Calculation
______ counts per minute
(cpm)
cpm * 2 hours * 60 min/hr
= __________ counts
cpm * 10 hours * 60 min/hr
= ____________ counts
Place the lantern mantle in your pocket and take a open window measurement.
If you leave it there for 2 hours, how many counts does your leg “see”?
If you leave it there for 10 hours, how many counts does your leg “see”?

4. Distance
The farther away you are from a radiation source, the less exposure you will receive.
Compare this to sitting in front of a fireplace. You can sit directly in front or across the room.
If you are far from the source, your exposure will be much lower.

5. Distance Calculation ______ cpm
Measure the radiation level at the surface of the plate or mantle.
Move 2 inches away, repeat the measurement.
Move 1 foot away, repeat the measurement.
Calculate the Distance Factor
DF = Contact (cpm) ÷ Distance (cpm)

6. Shielding
If you increase the shielding around a radiation source, it will decrease your exposure.
If you stand out in the rain without an umbrella, you will get wet.
But, if you use an umbrella to shield you from the rain, you will remain dry and protected.

7. Shielding Factor Calculation
______ cpm
Measure the radiation level on contact with a source using the open window detector.
Place a light piece of material (wood) over the object and repeat the measurement.
Place a heavy piece of material over the object and repeat the measurement.
Calculate Shielding Factor.
SF = Contact (c/m) ÷ Shielded (c/m)

8. Types of Radiation

9. Detector Efficiency By Radiation Type
Voltage Source
Incident
Ionizing
Radiation + + +
Electrical
Current
Measuring
Device - - -
Anode +
Cathode -

10. Beta and Gamma Activity Calculation
Measure the “gamma” radiation level on contact with a source using the closed window detector.
Assuming the detector “sees” 1 out of every 100 gamma rays, calculate the gamma activity.
Measure the “beta” + “gamma” radiation level on contact with a source using the open window.
Calculate the “beta” cpm by subtract the “gamma” cpm from the total “beta” + “gamma” cpm.
Assuming the detector “sees” 1 out of every 10 beta particles, calculate the beta activity.
_________  (cpm)
 activity =  (cpm)  0.01 (dpm/cpm)
__________ dpm
___________ + (cpm)
 (cpm) = + (cpm) -  (cpm)
 activity =  (cpm)  0.1 (dpm/cpm)
____________ dpm