The improvement of the energy resolution in epi-thermal region of Bonner sphere

using boric acid solution moderator

H. Ueda1, H. Tanaka2, Y. Sakurai2

 

1Graduate School of Engineering, Kyoto University2Kyoto University Research Reactor Institute

Outline

1. Calculation of Bonner sphere response functions using polyethylene and boric acid solution as a moderator.

2. Comparison of energy resolution between two types of Bonner spheres.

3. Evaluation of the neutron spectrum at Kyoto University Reactor Heavy Water Neutron Irradiation Facility ( KUR-HWNIF )

Introduction

• RBE of neutron greatly vary depending on its energy, especially in epi-thermal region.

• It is difficult to obtain the detailed information for the neutron energy spectrum in the keV region.

• We are improving the energy resolution of Bonner sphere, especially in the keV region, using the boric acid solution as a moderator.

Bonner Sphere1

moderator

Thermal neutron detector

Bonner Sphere2

1. Incidence

Neutron

2. Moderation to thermal energy

3. Detection

Moderator including 10B

Thermal NeutronAbsorbed by 10B

Epi-thermal NeutronThermalized near the center and detected

10B

Response function calculation

Parallel neutron beam

Thermal neutron detector• Manganin foil

(thickness: 200um, diameter: 2cm)

• Gold foil(thickness: 50um, diameter: 1cm)

Sphere diameter• 10, 15, 20 cm

Moderator material• Polyethylene• Boric acid solution ( 0.14 10B wt%)

Calculation results

Moderator: polyethylene boric acid water (0.14 10B wt%)

Activation foil: Gold(197Au)

• The specific saturated activities per flux for each energy neutron were calculated as the response function of Bonner spheres

Unfolding test1• We performed unfolding tests for the comparison of energy resolution.• Saturated activities were calculated and errors were added to the data.• The data were unfolded into estimated spectrum by UMG unfolding package for each moderator Bonner sphere.

Examples of Neutron spectra used in the tests

Unfolding tests2

Moderator: polyethylene boric acid solution (0.14 10B wt%)

Unfolding test3

Moderator: polyethylene boric acid solution (0.14 10B wt%)

Unfolding tests4

Moderator: polyethylene boric acid solution (0.14 10B wt%)

Unfolding test5

Moderator: polyethylene boric acid solution (0.14 10B wt%)

Measurement at KUR-HWNIF

Bonner sphere

Stochastic errors : 3-5%

Influence of foil placement and solution concentration

• The estimated spectrum in epi-thermal region changed by twenty and a several percentage if the foil position varied by 5mm or the boric acid concentration did by 10B 0.03wt%.

Estimation of KUR-HWNIF spectrum

Conclusion

1. It was confirmed that boric acid solution moderator improves the energy resolution of the Bonner sphere in the keV region.

2. The estimated spectrum was in good agreement with the data from the previous study.

3. The estimated spectrum in epi-thermal region changed by twenty and a several percentage if the foil position varied by 5mm or the boric acid concentration did by 10B 0.03wt%.

Thank you very much for your attention.

Response Functions1

Moderator: polyethyleneActivation foil: manganin(55Mn)

Moderator: polyethyleneActivation foil: gold(197Au)

Response Functions2

Moderator: boric acid water(0.14wt%)Activation foil: manganin(55Mn)

Moderator: boric acid water(0.14wt%)Activation foil: gold(197Au)