Some Lessons Learned from MCNP Usage

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Some Lessons Learned from MCNP Usage

• Robin P. Gardner, Libai Xu, Walid A. Metwally,
  and Dan Speaker
• Center for Engineering Applications of
  Radioisotopes
• North Carolina State University
• September 6th 2006

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Outline

• Unexpected density log peaks with spatial
  position
• Unexpected correlated sampling effects with
  density logs
• Spectroscopy binning effects
• Spectroscopy Gaussian spreading

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Unexpected Density Log Peaks
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CTZ
Reference M. B. Holstad, G. A. Johansen,
Scattered Gamma Radiation Utilized for Level
Measurement in Gravitational Separators, IEEE
Sensors Journal, Vol. 5, No. 2, 2005
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Alberto Mendoza et. al. (2005), Monte Carlo
Modeling of Nuclear Measurement in Vertical and
Horizontal Wells in the Presence of Mud-filtrate
Invasion and Salt Mixing, SPWLA 46th Annual
Logging Symposium, June 26-29
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Unexpected correlated sampling effects
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Same initial seed for different position, but
the seed is different from the previous case
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different seeds for different positions
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Spectroscopy Binning Effects
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90 Channels Even Between 0 and 900 keV
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900 Channels Even Between 0 and 900 keV
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10 keV Increments Between 0 and 500 keV 2 keV
Increments Between 500 and 600 keV and 4 keV
Increments Between 600 and 700 keV
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10 keV Increments Between 0 and 500 keV 2 keV
Increments Between 500 and 600 keV and 4 keV
Increments Between 600 and 700 keV
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10 keV Increments Between 0 and 500 keV 4 keV
Increments Between 500 and 700 keV
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10 keV Increments Between 0 and 500 keV 20 keV
Increments Between 500 and 620 keV and 5 keV
Increments Between 620 and 720 keV
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Spectroscopy Gaussian Spreading

W. A. Metwally, R. P. Gardner, and Avneet Sood,
Gaussian Broadening of MCNP Pulse Height
Spectra, Trans. of ANS, vol. 91, pp. 789-790,
2004
Heath, R.L., 1964, Scintillation
Spectrometry Gamma-Ray Spectrum Catalogue,''
IDO-16880-1. AEC Research and Development Report,
Physics, TID-4500.
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• How MCNP simulates Gaussian broadening?
• Particle energy is changed before it is tallied
  by randomly sampling an energy to be deposited
  from a Gaussian distribution centered at the
  original particle energy.
• Our proposed idea.
• Broadening process is performed at the end of
  simulation.

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• Simulation Testes

3 3NaI
Cs137

• MCNP broadening, 1 million histories.
• MCNP broadening, 10 million histories.
• MCNP broadening, 100 million histories.
• Our broadening, 1 million histories.

a0 b0.05086 c0.30486
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• Thank You