1. Modeling the Effects of a Radiological Dispersion Device Detonation
Tragan Knight and Nathaniel Tidwell
Dr. Melanie Sattler, P.E.
Dr. Yvette Weatherton, P.E.
Roja Haritha Gangupomu

2. Nathaniel Tidwell Completed first year at North Central Texas College
Attending University of Texas Arlington as a sophomore
Majoring in Mechanical Engineering

3. Tragan Knight Eastfield College University of Texas at Arlington
Major: Civil Engineering (Environmental Engineer)
Goals: Master (Material in Science) Ph.D.: (Theology)
Aspirations: Reevaluate and innovate the recycling process.

4. Objectives
Model the effects of a dirty bomb detonation at Cotton Bowl Stadium in Dallas, Texas
Use the HotSpot air dispersion model to run simulations
Compare different radionuclides, as well as various atmospheric conditions

5. Radiological Dispersion Devices
Also known as RDDs, or “dirty bombs”
Use conventional explosives to spread radioactive material over an area
Although there is concern that terrorist groups may use dirty bombs, so far none have actually been detonated.

6. Radionuclides Isotopes that undergo radioactive decay
Several types of radionuclides are used in medicine and industry
We used three different radionuclides in our simulations: 241Am, 137Cs, and 60Co
This backscatter gauge, used in industry, contains 137Cs.1
1 Nitus Gamma Backscatter Gauge. Digital image. ThermoScientific.com. Thermo Fisher Scientific Inc., n.d. Web. 23 July 2012.

7. Radiation Three types of radioactive decay Alpha Beta Gamma
Helium nucleus (alpha particle) is emitted from an atom
Most harmful, but least penetrating
Beta
Electron or positron (beta particle) is emitted
Moderate harm, and moderate penetration
Gamma
Gamma rays are emitted
Least harmful, but highly penetrating

8. Total Effective Dose Equivalent
Sum of external and internal effective dose equivalents
Unit of measure is the Sievert (Sv) or roentgen equivalent in man (rem) for biological tissue
1 Sv = 100 rems

9. Biological Effects of Radiation1
Effect
Dose
Blood count changes
50 rem
Vomiting (threshold)
100 rem
Mortality (threshold)
150 rem
LD50/60* (with minimal supportive care)
320 – 360 rem
LD50/60 (with supportive medical treatment)
480 – 540 rem
100% mortality (with best available treatment)
800 rem 
* The LD50/60 is that dose at which 50%of the exposed population will die within 60 days.
1"Biological Effects of Ionizing Radiation." Princeton.edu. Trustees of Princeton University, 30 Apr Web. 26 July 2012.

10. Air Dispersion Modeling
Often used to predict downwind concentrations of pollutants, especially from smokestacks
We used HotSpot to model an RDD detonation, which uses the Gaussian Plume Model.
𝐶= 𝑄 2𝜋𝑢 𝜎 𝑦 𝜎 𝑧 exp −𝑦 𝜎 𝑦 exp − 𝑧−𝐻 𝜎 𝑧 exp − 𝑧+𝐻 𝜎 𝑧 2

11. Plume Model

12. HotSpot
Created by National Atmospheric Release Advisory Center (NARAC)
A computer program designed to calculate radiation doses
Uses the Gaussian Equation
Provides numerous amounts of potential radiological dispersal devices scenarios
Used for short-term, short-range (up to 10 km) simulations

13. HotSpot 2.07.2 Relatively simple surroundings data
Built-in standard terrain information
One meteorological condition per run
Less sophisticated than other air dispersion models

14. Parameters
Variables
Radionuclide
Stability Class
Rainfall
241Am B
Rain
137Cs D
No Rain
60Co F
Mixture
4 radionuclides * 3 stability classes * 2 rainfall conditions = 24 runs

15. Other Parameters Material-at-Risk 100 grams High Explosives
100 pounds TNT equivalent
Wind Speed
4.8 m/s
Wind Direction
180° (from the south)
Rainfall Rate
5 mm/hr
Terrain
city

16. Running Simulations HotSpot is very user-friendly
It takes only a couple minutes to input terms and view results

17. Examples of Outputs

18. Results
Inputs and Outputs from Hotspot.

19. Results
Comparing differences in stability classes with 241Am B D F

20. Results
The figures below compare rainout and dry conditions using 60Co and stability class B.
No Rain Rain

21. Results
Comparing each isotope in dry conditions with stability class B
(a) 241Am
(b) 137Cs
(c) 60Co
(d) Mixture A B C D

22. Conclusions 60 Co generally had the highest TEDE
137 Cs generally had the lowest TEDE
Radiation doses are higher in scenarios with rain
Stability Class F had the largest isopleth area of sickness in all scenarios
Worst-case scenario is 60Co, stability class F, in rainy conditions

23. Thank You!