1. Limiting Effects of Ionizing Radiation

2. Presentation and Debate Teams
Tyler/Patrick – Con side in debate
Aaron/Jason – Pro side in debate
Danielle/Tim – Pro side in debate
Jessica/Josh – Con side in debate
Nick/Raquel – Con side in debate
Kristin/Cortney – Pro side in debate
Sean B./Zack – Pro side in debate
Cameron/Sean P. – Con side in debate

3. Presentation and Debate Team Feedback Form
Pros/Cons Feedback Form
Presenting Team ____________ Date ________
Time __ Research __ Materials __ Pros/Cons __
I really liked ________ about your presentation.
(One copy to the team and one to the instructor)
Debate Feedback Form
Debate Teams ____________ Date ________
Convincing _ Research _ Presenting _ Debate _
I really liked ______ when you debated your point.
(One copy to the team and one to the instructor)

4. GLE
Define Curie, understand and work with concept of point source and inverse square relationship.
Describe the concept of tenth thickness.
Describe methods for limiting worker’s exposure to ionizing radiation.
Objective
Student will define the Curie and understand the inverse squared relationship between radiation level and distance from a radioactive “point” source, understand and work with the concept of tenth thickness of different types of materials, and discuss the use of time/distance/shielding to reduce workers’ exposure to ionizing radiation.

5. Curie
Amount of ionizing radiation that will produce an exposure rate of 1 REM per hour at a distance of 1 meter from the source.

6. Radiation Dose Rate vs. Distance From Source
This relationship is for a “point” source
A point source approximates a spherical source of ionizing radiation
As distance increases away from a point source the radiation dose rate decreases with an “inverse-squared” relationship
From the definition for a Curie – At one meter from the source the dose rate is 1 Rem/hr
Moving to 2 meters away, increasing the distance by a factor of 2, causes a factor of 4 decrease in the dose rate = .25 Rem/hr or mRem/hr
Calculate the dose rate if the distance away changes to 4 meters away.

7. Shielding and Tenth Thickness
Different types of materials will shield different types of radiation more effectively.
Concern is with the most penetrating forms of radiation, if we shield these types then the less penetrating forms will also be shielded against
Will shield for neutrons and gammas.

8. Tenth Thickness for Neutrons
Tenth thickness is that thickness of the material that will reduce the ionizing radiation level to one-tenth of it’s initial value
What works best for neutrons?
Materials that are able to absorb maximum energy per collision and “reflect” the neutrons back toward the reactor core
Materials with lots of Hydrogen
Use H2O as neutron shielding
Tenth Thickness is 12 inches
What happens when we use 24 inches of H2O?

9. Tenth Thickness for Gammas
Tenth thickness is that thickness of the material that will reduce the ionizing radiation level to one-tenth of it’s initial value
What works best for gammas?
Materials that are relatively dense and able to absorb maximum energy caused by the “ionizations” caused by the gamma interactions
Materials that are relatively dense – lead and steel
Can use the steel as a structural material for the facility and to support the denser but more malleable lead
Tenth Thickness of lead for gammas is 2 inches
Tenth Thickness of steel for gammas is 4 inches

10. Limiting Exposure to Radiation
From what we have just discussed, brain storm some methods to limit or reduce a worker’s exposure to ionizing radiation.
Time
Distance
Shielding

11. Time
Fairly straight forward, limiting the time in a radiation field – worker receiving a dose rate – limits the total dose received

12. Distance
From our discussion of the inverse square relationship – getting the worker further from the source of the radiation causes a significant reduction in the dose rate

13. Shielding
Use of portable shielding will reduce by either half values (half thickness) or tenth values (tenth thickness)
Give examples of when you might have worn a lead apron as shielding.

14. Pros/Cons Presentation
Give example of previous student’s work
Have each student fill out a feedback form and discuss with class what score and comment they would have given for the presentation

15. WORK ON YOUR PRESENTATIONS/DEBATES
Homework
WORK ON YOUR PRESENTATIONS/DEBATES
Check for missing work – especially the Changes of State and Energy Content of Foods labs.