Limiting Effects of Ionizing Radiation

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

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)

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.

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.

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 250 mRem/hr Calculate the dose rate if the distance away changes to 4 meters away.

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.

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?

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

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

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

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

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.

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

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.