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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)