Tsutomu Tada

Equilibrium and kinetic studies of selective adsorption and separation for strontium using DtBuCH18C6 loaded resin

A crown ether loaded resin was prepared by successive impregnation and fixing the 4′,4′(5″)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its molecule modifier, 1-dodecanol, onto the porous silica/polymer composite support (SiO2-P particles). The characterization of DtBuCH18C6 loaded resin was examined by thermal gravimetry and differential thermal analysis and electron probe microanalysis. The adsorption behavior of Sr(II), Cs(I), Ru(III), Pd(II), La(III), Nd(III), Sm(III), Gd(III), Zr(IV), and Mo(VI) was investigated by the batch method. Furthermore, the column test for Sr (II) was performed. The batch experiments were carried out by varying the shaking times, HNO3 concentration, and initial concentration of metal ions. A relatively large K d value above 182 cm3/g for Sr(II) was obtained in the presence of 3 M HNO3. In contrast, the K d values of Cs(I), Ru(III), Pd(II), La(III), Nd(III), Sm(III), Gd(III), Zr(IV), and Mo(VI) were considerably lower than 10 cm3/g. The adsorption of Sr(II) was found to be controlled by chemisorption mechanism, and followed a Langmuir-type adsorption equation. The breakthrough curve of Sr(II) had S-shaped profile, and the elution percentage was estimated to be 99.9% by using the eluent of H2O.

Timing Performance of TlBr Detectors

The timing performance of TlBr detectors was evaluated at room temperature (22 °C). 0.5-mm-thick planar TlBr detectors with Tl circular electrodes with a diameter of 3 mm were fabricated from TlBr crystals grown by the traveling molten zone method using a zone-purified material. The pulse rise time of the TlBr detector was measured using a digital oscilloscope as the cathode surface of the device was irradiated with a 22Na gamma-ray source. Coincidence timing spectra were obtained between the TlBr detector and a BaF2 scintillation detector when both detectors were irradiated with 511 keV positron annihilation gamma-rays. The timing resolution of the TlBr detector was found to be inversely proportional to the applied bias voltage. The TlBr detector, in coincidence with the BaF2 detector, exhibited timing resolutions characterized by a 6.5 ns full width at half maximum (FWHM) and an 8.5 ns FWHM with and without an energy window of 350 keV-560 keV, respectively.

TlBr Capacitive Frisch Grid Detectors

Capacitive Frisch grid detectors with the dimensions of 2 mm × 2 mm × 4.4 mm were fabricated from TlBr crystals grown by the travelling molten zone method using zone-purified materials. Spectroscopic performance of the detectors was evaluated at room temperature (24°C), - 5°C and - 20°C. The TlBr detector exhibited an energy resolution of 1.6% FWHM at 662 keV with a peak-to-Compton ratio of 8.7 with the depth correction at room temperature. Improvement of the detector performance was achieved by cooling the detector-preamplifier system. The energy resolutions of 3.4%, 1.5%, 1.0% and 0.9% FWHM at 122 keV, 356 keV, 662 keV and 1332 keV, respectively, were recorded with the TlBr detector without the depth correction at - 5°C. An energy resolution of 0.9% FWHM at 662 keV with a peak-to-Compton ratio of 18.2 was obtained from the TlBr detector with the depth correction at -20°C. An upper limit for the Fano factor of TlBr was estimated to be 0.43 at -20°C.

Characterization of Thallium Bromide Detectors Made From Material Purified by the Filter Method

Thallium bromide (TlBr) has been regarded as candidate detector materials for the gamma-ray spectrometers operating at room temperature. In this study, a simple and rapid method, the filter method, was performed to purify a raw TlBr material used for fabrication of TlBr detectors. The material was loaded on shards of crashed quartz and installed in a Pyrex tube, and was melted using a furnace. A purified material passing through interspaces of the shards of quartz was collected in a quartz ampoule located at the outlet of the Pyrex tube. After the purification, impurities colored black extracted from the raw material remained. TlBr crystals were then grown by the travelling molten zone method both from the raw material and the purified material. TlBr detectors were fabricated from the grown crystals, and were characterized by measuring mobility-lifetime products (μτ) for carriers and gamma-ray spectra ( 137Cs) at room temperature. μτ for electrons of a TlBr detector fabricated from the purified material was around 5 times higher than that of a detector fabricated from the raw material.

PIXE STUDY ON THE GROWTH ENVIRONMENT OF PLANTS

Growth environment of plants was investigated by analyzing the elemental concentration in leaves of the plants. Camellia was selected as the sample and the leaves of the camellias were collected from Miyagi and Chiba prefectures. The species of elements and their concentrations in the leaves were measured by the in-air PIXE system at Tohoku University. More than 10 elements were detected from the leaves. The concentrations of Mn, Fe, and Rb in the leaves were strongly affected by the place where the tree grew. On the other hand, the concentration of P, S, K, and Ca were less affected by the place of the tree. The determination of the place of the tree was also performed by evaluating the similarity of the elemental concentration in the leaves quantitatively. The difference due to the place was clearly identified and the sampling place was successfully determined by using the elemental concentrations in the leaves.

Characterization of thallium bromide crystals purified by the filter method

Thallium bromide (TIBr) has been regarded as candidate detector materials for the gamma-ray spectrometers operating at room temperature. In this study, a simple and rapid method, the filter method, was performed to purify a raw TIBr material used for fabrication of TIBr detectors. The material was loaded on shards of crushed quartz and installed in a Pyrex tube, and was melted using a furnace. A purified material passing through interspaces of the shards of quartz was collected in a quartz ampoule located at the outlet of the Pyrex tube. After the purification, impurities colored black extracted from the raw material remained. TlBr crystals were then grown by the travelling molten zone method both from the raw material and the purified material. TlBr detectors were fabricated from the grown crystals, and were characterized by measuring mobility-lifetime products (μτ) for carriers and gamma-ray spectra (137Cs) at room temperature. μτ for electrons of a TlBr detector fabricated from the purified material was around 5 times higher than that of a detector fabricated from the raw material.

Recent development of TlBr gamma-ray detectors

Planar detectors, strip detectors, and double-sided strip detectors were fabricated from TlBr crystals grown by the traveling molten zone method using zone-purified material. The detector performance including the leakage current, energy resolutions, and timing performance were evaluated in order to assess the capability of the detectors for PET and SPECT applications. The TlBr detectors exhibited excellent spectroscopic performance at room temperature. An energy resolution of 3.4% FWHM at 511 keV was obtained from a TlBr planar detector 1 mm thick. A TlBr strip detector 1 mm thick with four anode strip electrodes exhibited almost uniform detector performance over the strips with the average energy resolution of 4.4% FWHM at 511 keV. A TlBr double-sided strip detector exhibited an energy resolution of 6.3% FWHM for 122 keV gamma-rays. Coincidence timing spectra between a TlBr planar detector and a BaF2 scintillation detector were recorded at room temperature. Timing resolutions of 14 ns and 24 ns were obtained from TlBr detectors 0.5 mm and 1 mm thick, respectively. By cooling the detector to 0° C, an improved timing resolution of 12 ns was obtained from a TlBr detector 1 mm thick.