Calculation of Response matrix of a BSS with ⁶LiI scintillator

H.R. Vega–Carrillo* ^{a , b} I. Donaire^c, E. Gallego^c, E. Manzanares–Acuñaª, A. Lorente^c, M.P. Iñiguez^d, A. Martin–Martin^d, and J.L. Gutierrez–Villanueva^d

ª Unidades Académicas de Estudios Nucleares e Ingeniería Eléctrica * Correspondig author e–mail: fermineutron@yahoo.com

^b Universidad Autónoma de Zacatecas, apartado postal # 336, 98000 Zacatecas, Zac. México.

^c Departamento de Ingeniería Nuclear de la Universidad Politécnica de Madrid, Spain.

^d Departamento de Física Teórica, Atómica y Optica, Laboratorio LIBRA de la Universidad de Valladolid, Spain

Recibido el 14 de mayo de 2007
Aceptado el 26 de octubre de 2007

Abstract

The response matrix of a Bonner sphere spectrometer was calculated using MCNP 4C and MCNPX 2.4.0 codes. As thermal neutron detector a 0.4 cm x 0.4 cm ⁶ LiI which is located at the center of a set of polyethylene spheres. The response was calculated for 0, 2, 3, 5, 8, 10, and 12 inches–diameter polyethylene spheres for neutrons whose energy goes from 2.50E(–8) to 100 MeV. The response matrix was calculated for 23 neutron energies, the response functions were energy–interpolated to 51 neutron energies and were compared with a matrix response reported in the literature, in this comparison both response matrices are in agreement. The main differences were found in the bare detector and are attributed to the irradiation conditions and cross sections, for the other detectors the differences are due to the cross sections libraries.

Keywords: Monte Carlo; ⁶LiI scintillator; Bonner sphere neutron spectrometer.

Resumen

Se calculó la matriz de respuesta de un espectrómetro de Esferas de Bonner utilizando los códigos Monte Carlo MCNP 4C y MCNPX 2.4.0. El detector de neutrones térmicos del espectrómetro es un centellador cilindrico, 0.4 cm X 0.4 cm, de ⁶LiI, que se ubica en el centro de esferas de polietileno. La respuesta se obtuvo para esferas cuyo diametro es 0, 2, 3, 5, 8, 10 y 12 pulgadas y para fuentes monoenergéticas de neutrones de 2.50E(–8) to 100 MeV. La matriz se calculó para 23 fuentes monoenergéticas, las funciones de respuesta se interpolaron a 51 energías que se compararon con las correspondientes reportadas en la literatura. Se encontró que ambas matrices son coincidentes, excepto para neutrones de baja y alta energía; esta diferencia es atribuida a las condiciones de irradiación utilizadas en ambos estudios y a las secciones eficaces.

Descriptores: Monte Carlo; centellador ⁶LiI; espectrometro de esferas de Bonner.

PACS: 24.10.Lx; 29.40.Mc; 29.30.–h

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Acknowledgments

This work is part of the SYNAPSIS project supported by CONACyT (México) under contract SEP–2004–C01–46893.

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