PHOBIA: Photon Buildup Factors to Account for Angular Incidence on Shield Walls.

No retrieval program is included.

Los Alamos National Laboratory, Los Alamos, New Mexico.

North Carolina State University, Raleigh, North Carolina.

Radiation Oncology Department, Washington University School of Medicine, St. Louis MO

PHOBIA (PHOton Buildup In Angles) slant-path buildup factors were calculated for photons in the energy range of 1 keV to 10 MeV for nine radiation safety and shielding materials (air, aluminum, concrete, iron, lead, leaded glass, polyethylene, stainless steel, and water). The data provide extensive improvement to the analysis capabilities of the Pandemonium code originally developed by the Stockpile Complex Modeling & Analysis Group at LANL. (PANDEMONIUM is not yet available for public distribution.) These photon buildup factors were calculated with the most recent cross-section data and a newly established group structure accommodating the necessary energy range extension. The ambient dose equivalent (hence abbreviated dose) buildup factors were analyzed at lower energies where corresponding response functions do not exist in literature.

The buildup factors utilized the following LANL codes: CEPXS, NJOY, and PARTISN. MCNPX was also used to provide a comparison to a few representative PARTISN buildup factor values. These codes are not included in this distribution but can be obtained from RSICC or the NEADB. Sample input files for these codes can be found in the appendix of the thesis.

Slant-path photon buildup factors for nine radiation shielding materials (air, aluminum, concrete, iron, lead, leaded glass, polyethylene, stainless steel, and water) are calculated with the most recent cross-section data available using Monte Carlo and discrete-ordinates methods. Discrete-ordinates calculations use a 244-group energy structure based on previous research at Los Alamos National Laboratory (LANL), and focus on the effects of group widths in multigroup calculations for low-energy photons. Buildup-factor calculations in discrete ordinates benefit from coupled photon/electron cross sections to account for secondary photon effects. Also, ambient dose equivalent buildup factors were analyzed at lower energies where corresponding response functions do not exist in the literature. The results of these studies are directly applicable to radiation safety at LANL, where the dose modeling code PANDEMONIUM is used to estimate worker dose in plutonium handling facilities. Buildup factors determined in this work will be used to enhance the code’s modeling capabilities but also should be of general interest to the radiation shielding community.

The data are distributed in a Microsoft Office EXCEL file.

EXCEL on X86 PC Windows; RSICC ID: D00236PCX8600.

Runtimes varied based on the material composition, the mean free path, photon energy level, and photon incident angle. In all cases, the PARTISN calculations were achieved in seconds to minutes, while the MCNPX calculations ranged from minutes to hours.

**a. Documentation available
with library**

F. G. Schirmers, *Improvement of Photon Buildup Factors
for Radiological Assessment*, Thesis NCSU, Raleigh, North Carolina (April
19, 2006), LA-14296-T (July 2006).

**b. Other useful
documentation**

D. Kornreich and D. Dooley, *PANDEMONIUM: Bringing Order
to Dose in Complicated Glovebox Arrays*, LA-UR-99-2765, Los Alamos National
Laboratory (1999).

Fritz G. Schirmers, *et al.*, “Calculation of Photon
Exposure and Ambient Dose Slant-Path Buildup Factors for Radiological
Assessment,” *Nuclear Technology*, **167 (3)**, pp 395-409 (September
2009).

Included are the document referenced in 10.a and a CD which contains a ZIP file with the buildup factor data in a Microsoft Excel file. Appendices B and D are included as separate pdf files.

December 2009.

**KEYWORDS:** BUILDUP FACTORS; GAMMA-RAY CROSS
SECTIONS