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Adding Dose Equivalent Scoring for Heavy Ions in FLUKA

Adding Dose Equivalent Scoring for Heavy Ions in FLUKA. Toni Empl & Lawrence Pinsky University of Houston. Current NASA Funding Status.

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Adding Dose Equivalent Scoring for Heavy Ions in FLUKA

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  1. Adding Dose Equivalent Scoring for Heavy Ions in FLUKA Toni Empl & Lawrence Pinsky University of Houston Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  2. Current NASA Funding Status • We have a specific grant from NASA/JSC to add Dose Equivalent Scoring into FLUKA (to support Toni through July). Kerry Lee and Neal Zapp continue to use FLUKA for operational calculations. • NASA is interested in having an “Advanced” FLUKA Course at some point in the not too distant future. • No word yet on possible extensions to validate codes for Light Fragments… • Funding to add a “Medipix (Si Charge Cluster) Simulation” to FLUKA is pending… • Tom Wilson has a proposal in to fund the use of FLUKA to model Lunar habitats and potential Lunar-based experiments Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  3. Dose Equivalent for Heavy Ions • Much of the effort has been done for protons and can be directly implemented for Heavy ions (We will use the NCRP 132 Q Factors)… • Scoring at an interface is less problematic than within a volume, (except for neutrals). • Principal Issues: • Neutrons (Multi-Group—Kerma)… • Double counting energetic d-rays… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  4. Neutron Issues • When a (multi-group) neutron is propagating in a medium the Kerma is normally scored and the neutron’s group is changed. • Scoring Dose Equivalent properly, one should propagate the neutron in detail and account for the energy deposits via any produced charged particles from interactions, much like a g. • This is problematic at surfaces. • Proposed Solution: Update Kerma tables in FLUKA to account for the Oxygen in Water, using a water equivalent scoring. Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  5. LET∞ Issues & Double Counting • The NCRP definition of Dose Equivalent for Heavy Ions employs an LET∞–based formula. • If one uses the actual Net Energy Lost by the particle over its track-length in a volume to be scored, and in addition propagates the long range d-rays does one count the deposition from them in addition to the energy lost by the primary, both when the d-ray remains entirely within that volume, and when it leaves the volume for an neighboring volume to be separately scored? • The same issue occurs for gamma’s produced. • A biological argument would be to score both… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  6. Recent Efforts in the Development of a TimePix-Based Active Dosimeter for Use in theSpace Radiation Environment Lawrence Pinsky (& Others) University of Houston Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  7. A Report on the TimePix @ HIMAC In February, 2009 Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  8. HIMAC @ NIRS in Japan • HIMAC - (Heavy Ion Medical Accelerator Center) @ NIRS (National Institute for Radiological Sciences) in Chiba, Japan. • Primarily a Cancer Therapy Center, but they give us free beam time Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  9. HIMAC Layout Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  10. Some “Standard” HIMAC Beams The Numbers in BLACK are the dE/dx values in Si, and the “*” are Non-Standard Beams. The Numbers in RED are the maximum kinematically allowed d-Ray energies. Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  11. Measuring Charge AND Energy • If you know b then measuring the charge is reasonably simple because of the Z2 dependence. • In accelerator experiments the interaction fragments from the projectile particle is generally moving at close to the projectile’s original velocity, at least for forward fragments. • However, if you have no a priori velocity information, the problem is the BETHE-BLOCH Equation… All charge-1 particles. Higher charge particles are raised by the square of the charge at the same momenta Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  12. Same dE/dx, BUT, Different Z Remember, these dE/dx values are from the Bethe-Bloch Equation! Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  13. dE/dx vs. Energy Deposited 180 MeV/A Ne 600 MeV/A Si 800 MeV/A Si 100 MeV/A O Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  14. High Energy d-Rays • Because the number of d-rays produced per unit track length in the Air prior to entering the Si is much less than in the the Si… • …The highest energy d-rays carry away more energy from the Si than enters from the air. • HOWEVER—It is the High Energy d-rays that offer the prospect of telling the difference between the different particle velocities with the same dE/dx… TimePix Air d-Rays Incident Particle Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  15. TimePix in the HIMAC Beams • Data were taken in a parasitic mode with Fe @ 500 MeV/A, N @ 290 & 180 MeV/A and Si @ 400 MeV/A • The primary beams were: • Si @ 600 & 800 MeV/A, • Ne at 180 MeV/A and • O @ 100 MeV/A, • all at Incident angles of 0, 15, 30, 45, 60& 90 • …With a TimePix clock of 20 MHz, IKRUM’s of 3, and with a Bias Voltages of 35V Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  16. Examples of Individual Tracks 100 MeV/A O 800 MeV/A Si 180 MeV/A Ne 800 MeV/A Si The high energy d-rays are clear in the higher energy tracks. These are not yet calibrated, and the study to be preformed is to explore the detailed resolution possible when all the information is included… The next goal is to be able to model these tracks in the FLUKA Monte Carlo code… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  17. The “Volcano” (Plasma) Effect • When the ionization creates a charge density that exceeds the doping density it can overwhelm them dielectric capability in the Si detector layer. • When that happens the charges “see” each other, and recombination increases considerably… • Also, when the track is parallel with respect to the bias field the recombination opportunity is a maximum. This can create a “hole” or dip in the center of the circular drift image, making the “lego-plot” look like a volcano… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  18. Close Up of the “Partial” Event • The right-hand event is a “normal” iron event, which does show a clear “Volcano” Effect. The scale is so high that the d-rays are not visible. • The left-hand event is a “Partial-Event.” One that was partially cutoff by the “Shutter.” • Because the central hole essentially goes to zero, it would appear that this event occurred at the end of the Shutter window and was only the early part of the drift image… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  19. Another view of the Volcano Event… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  20. The Next Steps… • The Chip has now been calibrated and absolute analyses in KeV are being started… • …And, we will also complete the measurement program at HIMAC… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  21. Using the TimePix to Measure Interaction Cross Sections… • There are many heavy ion interaction cross sections that will be needed to verify the existing event generators used to predict doses in astronauts will take on future space missions… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  22. Pixelman Frames from11B @ ~90 From Last Year Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  23. Image of Time of Arrival of Charge at the Chip… • We can examine the nature of the drift of the charge cloud by using the TDC capability of the TimePix… • See separate ABCDView Plot… Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

  24. Thank You for Your Attention Adding Dose Equivalent Scoring and Recent Efforts in the Development of a TimePix-Based Active Dosimeter

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