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Local coordination state of rare earth in eutectic scintillators for neutron detector applications.

Masai H, Yanagida T, Mizoguchi T, Ina T, Miyazaki T, Kawaguti N, Fukuda K - Sci Rep (2015)

Bottom Line: In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution.However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection.The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.

ABSTRACT
Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca(2+) ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu(2+) ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

No MeSH data available.


Related in: MedlinePlus

80LiF-20CaF2 eutectics containing different Eu concentrations.(a) Optical transmittance spectra of several eutectics and the appearances. SEM images of 0.005Eu (b), 0.02Eu (c), and 5Eu (d) -doped samples.
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f1: 80LiF-20CaF2 eutectics containing different Eu concentrations.(a) Optical transmittance spectra of several eutectics and the appearances. SEM images of 0.005Eu (b), 0.02Eu (c), and 5Eu (d) -doped samples.

Mentions: Figure 1(a) shows optical transmittance spectra of LiF/CaF2 eutectics containing different Eu concentrations (0.005, 0.1, and 5 mol%) with the inset graphic showing their appearances. They are visibly translucent or opaque with brownish coloration, and the opacity increases with increasing Eu concentration (also see Supplementary Fig. 1). Because the difference of the refractive index between CaF2 and LiF is less than 0.05 (~0.0417), it is expected that the low transparency, even in Eu-free samples, originates from a phase separation with micrometre size regions. Figure 1(b–d) show backscattered SEM images of these Eu-doped LiF/CaF2 eutectics. In these figures, brighter parts indicate the existence of heavier elements. Therefore, bright regions are CaF2 containing Eu cations, whereas the dark regions are due to LiF. Similar to previous reports161718, a lamella structure with a layer thickness of submicron-order is generated in the eutectics containing small amounts of Eu cations, which is one of the reasons for low transparency. The lamella structure is not oriented along a fixed direction in the sample but is partially oriented in a grain-like region with several hundred micrometres diameter, which is why no periodical absorption is observed in these transmittance spectra. On the other hand, the lamella structure no longer exists in the 1mol%-Eu doped eutectic, and precipitation of large size grains are observed in high Eu concentration samples. The decrease of transparency owing to such irregularity of the structure is shown in Supplementary Figs 2 & 3. It is notable that some aggregation of Eu cations is observed in the LiF/CaF2 eutectics with small Eu-doping. With increasing Eu concentration, there seems to be no aggregation spot in the matrix, suggesting that Eu cations are homogeneously dispersed in the CaF2 region.


Local coordination state of rare earth in eutectic scintillators for neutron detector applications.

Masai H, Yanagida T, Mizoguchi T, Ina T, Miyazaki T, Kawaguti N, Fukuda K - Sci Rep (2015)

80LiF-20CaF2 eutectics containing different Eu concentrations.(a) Optical transmittance spectra of several eutectics and the appearances. SEM images of 0.005Eu (b), 0.02Eu (c), and 5Eu (d) -doped samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4544017&req=5

f1: 80LiF-20CaF2 eutectics containing different Eu concentrations.(a) Optical transmittance spectra of several eutectics and the appearances. SEM images of 0.005Eu (b), 0.02Eu (c), and 5Eu (d) -doped samples.
Mentions: Figure 1(a) shows optical transmittance spectra of LiF/CaF2 eutectics containing different Eu concentrations (0.005, 0.1, and 5 mol%) with the inset graphic showing their appearances. They are visibly translucent or opaque with brownish coloration, and the opacity increases with increasing Eu concentration (also see Supplementary Fig. 1). Because the difference of the refractive index between CaF2 and LiF is less than 0.05 (~0.0417), it is expected that the low transparency, even in Eu-free samples, originates from a phase separation with micrometre size regions. Figure 1(b–d) show backscattered SEM images of these Eu-doped LiF/CaF2 eutectics. In these figures, brighter parts indicate the existence of heavier elements. Therefore, bright regions are CaF2 containing Eu cations, whereas the dark regions are due to LiF. Similar to previous reports161718, a lamella structure with a layer thickness of submicron-order is generated in the eutectics containing small amounts of Eu cations, which is one of the reasons for low transparency. The lamella structure is not oriented along a fixed direction in the sample but is partially oriented in a grain-like region with several hundred micrometres diameter, which is why no periodical absorption is observed in these transmittance spectra. On the other hand, the lamella structure no longer exists in the 1mol%-Eu doped eutectic, and precipitation of large size grains are observed in high Eu concentration samples. The decrease of transparency owing to such irregularity of the structure is shown in Supplementary Figs 2 & 3. It is notable that some aggregation of Eu cations is observed in the LiF/CaF2 eutectics with small Eu-doping. With increasing Eu concentration, there seems to be no aggregation spot in the matrix, suggesting that Eu cations are homogeneously dispersed in the CaF2 region.

Bottom Line: In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution.However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection.The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.

ABSTRACT
Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca(2+) ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu(2+) ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

No MeSH data available.


Related in: MedlinePlus