Neutron sprectra re-binning and dose calculation using Monte Carlo methods

H.R. Vega-Carrilloª ^{, b}, E. Manzanares Acuñaª, J.M. Ortiz Rodríguezª ^{, b}, and T. Arteaga Arteagaª ^,c

Unidades Académicas:
ª Estudios Nucleares,

^b Ing. Eléctrica, Universidad Autónoma de Zacatecas, Apartado Postal 336, 98000 Zacatecas, Zac. México, e-mail: fermineutron@yahoo.com

^c Envases de Zacatecas, SA de CV, Parque Industrial de Calera de Víctor Rosales, Zac. México

Recibido el 2 de marzo de 2006
Aceptado el 18 de agosto de 2006

Abstract

One hundred thirty lethargy neutron spectra in 60 energy groups were converted to energy spectra and re-binned to 31 energy groups. Original spectra were taken form the compilation published by the IAEA and covers neutron spectra from isotopic neutron sources, nuclear reactors, medical and physical application accelerators, cosmic rays, etc. The 31 energy groups were taken from the BUNKIUT unfolding code, which is utilized to obtain the neutron spectrum from a multisphere neutron spectrometer. Re-binned spectra were utilized to calculate the ambient, personal and effective doses covering 13 types of doses. This calculation was carried out through the ICRP74 dose-to-fluence conversion coefficients. This procedure was performed using Monte Carlo methods using the MCNP 4C code. Two experiments were carried out to obtain, with a Bonner sphere spectrometer, the BUNKIUT code and the UTA4 response matrix, the neutron spectra of ²⁵²Cf and ²⁵²Cf/ D₂O. For both sources and at the same locations the equivalent ambient dose were measured using a rem meter. Measured H*(10) and neutron spectra were compared with those obtained in the Monte Carlo calculations.

Keywords: Neutron spectrometry; dose; Monte Carlo.

Resumen

Ciento treinta espectros por unidad de letargia definidos en 60 grupos de energía se convirtieron en espectros por unidad de energía y se re-estructuraron a 31 grupos de energía. Los espectros originales se tomaron de la colección publicada por el OIEA y comprenden espectros producidos por fuentes isotópicas de neutrones, reactores nucleares, aceleradores de uso médico y de investigación en física, rayos cósmicos, etc. Los 31 grupos de energía se tomaron del código de reconstrucción de espectros BUNKIUT que se utiliza para obtener los espectros de neutrones a partir de las tasas de conteo de un espectrómetro de esferas de Bonner. Los espectros re-estructurados se utilizaron para calcular 13 dosis que incluyen la dosis equivalente ambiental, la dosis equivalente personal y la dosis efectiva. Este cálculo se realizó utilizando los coeficientes de conversion de fluencia a dosis del ICRP74. Los cálculos se realizaron utilizando métodos Monte Carlo mediante el código MCNP 4C. Mediante el uso de un espectrómetro de esferas de Bonner, el código BUNKIUT y la matriz de respuesta UTA4 se realizaron dos experimentos donde se determinaron los espectros de dos fuentes de neutrones: ²⁵²Cf y ²⁵²Cf/D₂O. Además de la determinación de los espectros de neutrones se midió el equivalente de dosis ambiental utilizando un dosímetro moderado de neutrones. Los valores de H*(10) y los espectros de neutrones se compararon con los espectros y las dosis obtenidas con los cálculos Monte Carlo.

Descriptores: Espectrometría de neutrones; dosis; Monte Carlo.

PACS: 29.30.Hs; 87.58.Sp; 87.53.Wz

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Acknowledgments

This work was partially supported by CONACyT (México) under contract SEP-2004-C01-46893.

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