Fabrication and characterization of large size 6LiF/CaF2:Eu eutectic composites with the ordered lamellar structure

doi:10.1016/j.nima.2011.02.009

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Volume 652, Issue 1, 1 October 2011, Pages 209-211

https://doi.org/10.1016/j.nima.2011.02.009 Get rights and content

Abstract

As alternative candidates for the ³He neutron detectors, ⁶LiF/CaF₂:Eu eutectic composites were fabricated and their scintillation properties were evaluated. Large size LiF/CaF₂:Eu eutectic composites of 58 mm diameter and 50 mm thickness were produced by Bridgman method. The composites had a finely ordered lamellar structure along the solidification direction. The lamellar structure was controlled by the direction and the rate of solidification, and it was optimized to improve the scintillation properties. Better results were achieved when thinner lamellar layers were aligned along the scintillation light path.

Introduction

Recently, the alternatives to ³He neutron detector are strongly desired as a result of crisis of ³He gas supply. ⁶LiF/ZnS composite scintillator is one of the candidates because of its low sensitivity to gamma-rays; thus it is widely used in neutron diffraction [1]. However, the opacity of this scintillator limits the detection efficiency for neutrons. From the viewpoint of detection efficiency, LiF/CaF₂ eutectic composite is an attractive material because it has high lithium content (Fig. 1). Furthermore, its semi-transparent nature allows the use of rather thick scintillator, and excellent neutron absorption can be achieved with a few mm thick LiF/CaF₂ scintillator (Fig. 1). The LiF/CaF₂ eutectic composite doped with Mn was first proposed for dosimeter applications in Ref. [2], and recently it was studied as a neutron scintillator when doped with Eu [3].

The objective of our current project is to control and optimize the lamellar structure of LiF/CaF₂ to achieve the best scintillation properties. In the present work, LiF/CaF₂:Eu with a finely ordered lamellar structure was produced and its scintillation properties for neutron detection were evaluated.

Section snippets

Fabrication of LiF/CaF₂:Eu eutectic composites

The Bridgman method (Fig. 2) was employed to produce LiF/CaF₂:Eu composites in order to achieve the ordered lamellar structure. In the unidirectional solidification processes such as Bridgman, Czochralski, or micro-pulling-down method, LiF and CaF₂ phases deposit from the melt on their own former solid phases. Thus, each phase grows along the solidification direction and the ordered structure can be achieved.

The starting material was prepared from high-purity (>99.99%) fluoride powders of LiF,

Lamellar structure of LiF/CaF₂:Eu

The as-produced LiF/CaF₂:Eu composites were 58 mm in diameter and 50 mm thick. Fig. 3 shows 1 mm thick samples cut across and along the solidification direction. The lamellar structure showed random shape across the solidification direction, but it had a well ordered wall shape along the growth (solidification) direction. The straight-wall structure of the CaF₂:Eu scintillator is expected to enhance the transmittance of scintillation light along the domain walls.

The samples were coupled to a PMT

Conclusions

Large size LiF/CaF₂:Eu eutectic composite blocks were produced by the Bridgman method. The lamellar structure of the specimens was controlled by the direction and the rate of solidification, and it was optimized to improve the scintillation performance. The results demonstrated that the faster solidified specimens had better energy resolution.

Thus, the unidirectional solidification process is a promising way for commercial production of such material. Since the composite ingots still had some

Acknowledgements

This work was partially supported by the Ministry of Health and Welfare, Grant-in-Aid for the development of medical instruments. This work was also partially supported by Ministry of Education, Culture, Sports, Science and Technology of Japanese government, Grant-in-Aid for Young Scientists (A), 19686001 (AY).

References (3)

Kaoru Sakasai et al.
Nucl. Instr. and Meth. A
(2009)

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Fabrication and characterization of large size 6LiF/CaF2:Eu eutectic composites with the ordered lamellar structure

Abstract

Introduction

Section snippets

Fabrication of LiF/CaF2:Eu eutectic composites

Lamellar structure of LiF/CaF2:Eu

Conclusions

Acknowledgements

Nucl. Instr. and Meth. A

Fabrication and characterization of large size ⁶LiF/CaF₂:Eu eutectic composites with the ordered lamellar structure

Fabrication of LiF/CaF₂:Eu eutectic composites

Lamellar structure of LiF/CaF₂:Eu