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A Monte Carlo Simulation of Energy Deposited in Scinti-Safe Plus 50% by a Charged ParticlePowerPoint Presentation

A Monte Carlo Simulation of Energy Deposited in Scinti-Safe Plus 50% by a Charged Particle

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A Monte Carlo Simulation of Energy Deposited in Scinti-Safe Plus 50% by a Charged Particle

- Maureen SikesUNC-Pembroke
- Natasha McNair: UNC-Greensboro
- Advisor: Dr. Tom Dooling-UNCP

A Monte Carlo Simulation of Energy Deposited in Scinti-Safe Plus 50% by a Charged ParticleMaureen Sikes: UNCPNatasha McNair: UNC-GreensboroAdvisor: Dr. Tom Dooling-UNCPAbstract

- In conjunction with an experimental study, a Monte Carlo program was created using FORTRAN to simulate the energy deposited in a liquid scintillator by a charged particle. The overall study examined whether light responses in an organic scintillating liquid were proportional to the amount of energy deposited in the scintillator by a charged particle. The study was carried out using common radiological sources as a preliminary step in the development of a radiological device to be used in response to a “dirty bomb” attack. This work was supported by the National Science Foundation's Research Experiences for Undergraduates program (CHE- 0353724).

What is a Monte Carlo? Plus 50% by a Charged Particle

- The Monte Carlo program is a software simulation of our experimental work, written in GNU Fortran
- The simulation helps us to better understand our experimental data.
- It can be used to develop new experimental models.
- Programs have been developed to simulate the behavior of a beta particle emitted from either a Strontium-90 or Thallium-204 source
- A program to simulate the behavior of gamma rays from a Cobalt-60 source is still in development

Event Generation Plus 50% by a Charged Particle

- First an event or simulated particle is created
- Simulated beta particles are assigned several initial properties through the use of random number generators
- The frequent use of random number generators in the program is why this type of program is called a “Monte Carlo”
- Initial Particle Energy
- First a particle must be assigned a random energy appropriate for the type of particle it is simulating
- Use the radioisotope’s maximum energy along with the random number generator
- Test the energy against the radioisotope’s beta decay spectrum to see if it’s a valid representation
- For an Strontium-90 source, will the beta particle simulate a Strontium or Yttrium emission?

Strontium-90 Beta Spectrum Plus 50% by a Charged Particle

Yttrium-90 Beta Spectrum Plus 50% by a Charged Particle

Thallium-204 Beta Spectrum Plus 50% by a Charged Particle

Cobalt-60 Beta Spectrum Plus 50% by a Charged Particle

Initial Properties Plus 50% by a Charged Particle

- Initial Position
- The particle is randomly assigned an initial x and y position within the source disc

- Random Angle
- The particle is also randomly assigned an angle in three dimensions at which it leaves the source

- Collimation
- The Strontium-90 and Thallium-204 sources were both experimentally tested two ways: collimated and un-collimated
- To simulated the physical restriction of collimation, an option was included in the angle generation section
- When selected, the particle was assigned only a path straight out of the source

Particle Tracking Plus 50% by a Charged Particle

- Now that the simulated particle has been assigned all of its initial properties, it leaves the source and we follow it as it passes through the simulated materials
- The program takes the particle through a series of materials corresponding to the actual materials used in the experimental setup
- Stopping Power
- Each material interacts differently with a charged particle
- Stopping power is a measure of how much energy is lost per centimeter in a given material and is a function of the energy of the particle

Stopping Power Plus 50% by a Charged Particle Table for Plastic Polymethyl Methacralate (Lucite, Perspex, Plexiglass)(Beta Energy Spectrum)

Stopping Power Table for ScintiSafe Plus 50% Cocktail – (Beta Energy Spectrum)

How Particles Travel (Beta Energy Spectrum)

- Particles travel through the materials one “step” at a time from their initial position
- For our simulations we defined a “step” to be 0.01cm
- After every “step” the particle’s current position, energy and applied conditions are reevaluated by the program

Material Selection and Energy Tracking (Beta Energy Spectrum)

- One of the factors recalculated after every step is how far the particle has traveled from the source
- This distance is used to tell the program which material the particle is passing through
- For example, the plastic material covering the source is defined to be from 0.0 cm to 0.05 cm away from the source
- After the particle has passed 0.05cm, it has moved on to the next material, Teflon
- After the material to be applied for a step is selected, the particle’s energy is put into the stopping power function for that material
- This calculates the stopping power to be applied in this step
- The stopping power value is used to calculate the mean energy loss for the step

Energy Spreading (Beta Energy Spectrum)

- When a charged particle actually passes through a material, the large number of collisions it incurs causes statistical variations
- This results in the actual energy loss not simply being the mean energy loss expected
- The energy loss is better illustrated as distribution of energy, not a direct shift
- This distribution is generally Gaussian in form, so it can be calculated and a correction factor applied
- After the energy spreading is applied, the corrected energy loss for the step is subtracted to get the energy of the particle in its next step

Sr-90 without Spreading (Beta Energy Spectrum)

Sr-90 with Spreading (Beta Energy Spectrum)

Sr-90 Experimental Data (Beta Energy Spectrum)

When to Stop Tracking (Beta Energy Spectrum)

- The particle has left the equipment
- The particle’s energy is too small
- When this occurs the program starts over with the creation of a new particle

Conclusions (Beta Energy Spectrum)

- Once the particle reaches the scintillating material the energy lost by the particle is tallied
- For each step (0.01cm) in the scintillating material some of the particle’s energy is deposited into the material
- This deposited energy is added to the energy from the previous steps
- The total energy deposited in the scintillating material is proportional to the light generated experimentally
- The program is run for 500,000 events, where each event represents one particle simulation
- This sufficiently reproduces the general shape of experimental energy distributions
- Therefore the program has strong predictive power

Results Sr-90 Collimated (Beta Energy Spectrum)

Noise Corrected Graphs Monte Carlo Graphs

Crun 01a – 2.5 cm of Scintillator Mrun 01a – 2.5 cm of Scintillator

Crun01b – 2.0 cm of Scintillator Mrun01b – 2.0 cm of Scintillator

Results Sr-90 Un-collimated (Beta Energy Spectrum)

Noise Corrected Graphs Monte Carlo Graphs

Crun02a – 2.5 cm of Scintillator Mrun02a – 2.5 cm of Scintillator

Crun02b – 2.0 cm of Scintillator Mrun02b – 2.0 cm of Scintillator

Results Tl-204 Collimated (Beta Energy Spectrum)

Noise Corrected Graphs Monte Carlo Graphs

Crun03a – 2.5 cm of Scintillator Mrun03a – 2.5 cm of Scintillator

Crun03b – 2.0 cm of Scintillator Mrun03b – 2.0 cm ofScintillator

Results (Beta Energy Spectrum)Tl-204 Un-collimated

Noise Corrected Graphs Monte Carlo Graphs

Crun04a – 2.5cm of Scintillator Mrun04a – 2.5cm of Scintillator

Crun04b – 2.0 cm of Scintillator Mrun04b – 2.0 cm of Scintillator

Acknowledgements (Beta Energy Spectrum)

National Science Foundation

Research Experience for Undergraduates

Program

At the University of North Carolina at Pembroke

Summer 2004

Funding made possible in part by grant

#CHE-0353724 from the National Science Foundation’s “Research Experience for Undergraduates” program

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