Investigación

 

Response matrix of a multisphere neutron spectrometer with an ³He proportional counter

 

H.R. Vega-Carrillo^a,b,c, E. Manzanares-Acuña^a, V Martín Hernández-Dávila^a,b, and G.A. Mercado Sánchez^c

 

^aUnidad Académica de Estudios Nucleares, Cuerpo Académico de Radiobiología de la Universidad Autónoma de Zacatecas Apartado Postal 336, 98000 Zacatecas, Zac. Mexico.

^b Unidad Académica de Ingeniería Eléctrica, Cuerpo Académico de Radiobiología de la Universidad Autónoma de Zacatecas Apartado Postal 336, 98000 Zacatecas, Zac. Mexico.

^c Unidad Académica de Matemáticas, Cuerpo Académico de Radiobiología de la Universidad Autónoma de Zacatecas Apartado Postal 336, 98000 Zacatecas, Zac. Mexico.

 

Recibido el 3 de marzo de 2004;
aceptado el 3 de diciembre de 2004

 

Abstract

The response matrix of a Bonner sphere spectrometer was calculated by use of the MCNP code. As thermal neutron counter, the spectrometer has a 3.2 cm-diameter ³He-filled proportional counter which is located at the center of a set of polyethylene spheres. The response was calculated for 0, 3, 5, 6, 8, 10, 12, and 16 inches-diameter polyethylene spheres for neutrons whose energy goes from 10~⁹ to 20 MeV. The response matrix was compared with a set of responses measured with several monoenergetic neutron sources. In this comparison the calculated matrix agrees with the experimental results. The matrix was also compared with the response matrix calculated for the PTB C spectrometer. Even though that calculation was carried out using a detailed model to describe the proportional counter; both matrices do agree, but small differences are observed in the bare case because of the difference in the model used during calculations. Other differences are in some spheres for 14.8 and 20 MeV neutrons, probably due to the differences in the cross sections used during both calculations.

Keywords: Monte Carlo simulations; neutron transport; gas filled counters.

 

Resumen

La matriz de respuesta de un espectrómetro de Esferas de Bonner ha sido calculada mediante el código MCNP. Como detector de neutrones térmicos se utilizó un contador proporcional de 3.2 cm de diámetro que se ubica en el centro de un conjunto de esferas de polietileno. La respuesta, ante neutrones de 10-9 a 20 MeV, se calculó para esferas cuyo diámetro es de 0, 3, 5, 8, 10, 12 y 16 pulgadas. La matriz de respuesta se comparó con un conjunto de respuestas determinado experimentalmente con varias fuentes de neutrones monoenergéticos. En esta comparación la matriz calculada coincide con los resultados experimentales. La matriz también se comparó con la matriz calculada para el espectrómetro PTB C donde el detector se modeló en forma detallada. De esta comparación, se observaron pequeñas diferencias debidas a que en esta investigación el detector se modeló en forma simple. Otras diferencias se observaron para algunas esferas y para neutrones de 14.9 y 20 MeV, la explicación probable de estas diferencias se atribuya a que en ambos cálculos se utilizaron versiones diferentes de los valores de las secciones eficaces.

Descriptores: Monte Carlo; transporte de neutrones; contador proporcional.

 

PACS: 24.10.Lx; 28.20.Gd; 29.40.Cs

 

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Acknowledgments

The authors gratefully thank Dr. Peter Wynn, visiting professor at UAZ, for his suggestions and discussions that helped to improve the manuscript.

 

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