Half-life determination of the ground state decay of 167Tm and 168Tm.

Precise determination of half-lives of 167Tm and 168Tm are important for their application in nuclear medicine diagnostics, nuclear forensics, and other nuclear data measurements. We produced 167Tm and 168Tm sources using an α-particle beam bombarded 165Ho target and a series purification steps. A series of 173 measurements was performed over a period of 44 days using a high-purity germanium (HPGe) detector to track the count rate change as a function of time by following the 207.8 keV and 531.5 keV γ-lines to determine the radioactive decay half-life of 167Tm. The measurement of half-life of 168Tm ground state has been performed using the same HPGe γ-ray spectrometer to observe γ-lines at 198.3 keV, 816.0 keV, 184.3 keV, 741.4 keV and 914.9 keV. Weighted least-squares fits of exponential decay curves were performed for the dataset of each γ-ray emission, with final determined half-lives of 9.250(15) d and 93.41(12) d for 167Tm and 168Tm, respectively. The uncertainty budgets are presented and discussed in detail. Our result of 167Tm half-life is consistent with the Evaluated Nuclear Structure Data File (ENSDF) recommended half-life of 9.25(2) d. The outcome of 168Tm half-life determination is longer than the ENSDF recommended half-life of 93.1(2) d. Further independent measurements would be ideal to resolve the discrepancy.

ω-transaminase-catalyzed synthesis of (R)-2-(1-aminoethyl)-4-fluorophenol, a chiral intermediate of novel anti-tumor drugs.

The chiral amine (R)-2-(1-aminoethyl)-4-fluorophenol has attracted increasing attentions in recent years in the field of pharmaceuticals because of its important use as a building block in the synthesis of novel anti-tumor drugs targeting tropomyosin receptor kinases. In the present study, a ω-transaminase (ωTA) library consisting of 21 (R)-enantioselective enzymes was constructed and screened for the asymmetric biosynthesis of (R)-2-(1-aminoethyl)-4-fluorophenol from its prochiral ketone. Using (R)-α-methylbenzylamine, D-alanine, or isopropylamine as amino donor, 18 ωTAs were identified with target activity and the enzyme AbTA, which was originally identified from Arthrobacter sp. KNK168, was found to be a potent candidate. The E. coli whole cells expressing AbTA could be used as catalysts. The optimal temperature and pH for the activity were 35-40 °C and pH8.0, respectively. Simple alcohols (such as ethanol, isopropanol, and methanol) and dimethyl sulfoxide were shown to be good cosolvents. High activities were detected when using ethanol and dimethyl sulfoxide at the concentrations of 5-20%. In the scaled-up reaction of 1-liter containing 13 mM ketone substrate, about 50% conversion was achieved in 24 h. 6.4 mM (R)-2-(1-aminoethyl)-4-fluorophenol was generated. After a simple and efficient process of product isolation and purification (with 98.8% recovery), 0.986 g yellowish powder of the product (R)-2-(1-aminoethyl)-4-fluorophenol with high (R)-enantiopurity (up to 100% enantiomeric excess) was obtained. This study established an overall process for the biosynthesis of the high value pharmaceutical chiral amine (R)-2-(1-aminoethyl)-4-fluorophenol by ωTA. Its applicable potential was exemplified by gram-scale production.

Half-life determination of 111Ag.

111Ag is a radionuclide that can be generated by neutron capture on 110Pd and whose decay properties and production feasibility make it a potential therapeutic agent against arthritis. Due to the discrepancies of recent published values of the half-life of 111Ag with previous published works which are not thoroughly documented for detailed experiment procedures and uncertainty budgets evaluation, an independent redetermination of the 111Ag half-life value is required. In this work, a solid 111Ag source was prepared and repeatedly measured in a high purity Germanium (HPGe) detector to determine its half-life. In total, more than fifty measurements were performed over a period of 26.3 days, corresponding to ∼3.5 half-lives of 111Ag. The experimental method and corresponding uncertainty budget are presented. The result of 7.419(15) days is consistent with the recently published value, 7.423(13) days, by Collins et al. and deviates by 0.418% from the currently recommended value 7.45(1) days. A new recommend half-life value of 7.437(7) days was determined utilizing all available experimental values by a power-moderated mean (PMM) method.

Determination of the half-life of 161Tb.

161Tb has potential applications in targeted radionuclide therapy and nuclear forensic science. However, the half-lives of 161Tb in previous studies show a discrepancy. In this study, 161Tb samples were produced by irradiating 160Gd2O3 with thermal neutron flux. A series of procedures were applied to extract a pure 161Tb solution and three solid samples were prepared. The half-life of 161Tb has been measured with a high-purity germanium (HPGe) detector. The time-dependency of the 161Tb activity was followed by assessing the count rate of their characteristic gamma-ray emissions at 48.9 keV and 74.6 keV over a period of 33-43 days. The experiment and uncertainty budget are discussed in detail. Different uncertainty propagation equations were applied for random uncertainties, medium-frequency deviations and potential systematic errors. The result for the 161Tb half-life of 6.967 (11) d was determined by the weighted mean of half-lives from three samples, which confirms that the half-life is longer than the of the current evaluated half-life of 6.89 (2) d. From all available quoted experimental values, a recommended half-life of 6.934 (14) d was determined by the power-moderated method (PMM). Based on recent four published half-life values, a half-life of 161Tb of 6.9582 (33) d was determined by the PMM analysis.

Anisotropic dielectric behavior of layered perovskite-like Cs3Bi2I9 crystals in the terahertz region.

The ternary metal halide perovskites have gradually attracted attention for application in the optoelectronic field, owing to their tunable crystal structure and appropriate bandgap. Lead free Cs3Bi2I9 perovskite, with a 0D layered structure containing molecular [Bi2I9]3- dimers, exhibits prominent optical and electrical anisotropies. Here, the anisotropic properties of the Cs3Bi2I9 crystals were evaluated using terahertz time-domain spectroscopy (THz-TDS); meanwhile, the effect of phonon vibration on the THz transmission was confirmed using density functional perturbation theory (DFPT). Accordingly, the refractive index and extinction coefficient are estimated using THz-TDS, thanks to the high transmission in the range of 0.2-0.9 THz. The anisotropic refractive index was observed for the Cs3Bi2I9 crystals, and was found to be 3.2-3.7 for the (100) plane (CBI(100)) in contrast to 2.8-3.2 for the (001) plane (CBI(001)). Furthermore, the Lorentz model was employed to extract the dielectric constant of Cs3Bi2I9, in which anisotropy is obviously indicated by the static dielectric constant and the high-frequency dielectric constant. These anisotropic behaviors are determined by the dipole moment, which is attributed to the anisotropic packing density of [Bi2I9]3- dimers. This study is significant and provides a deeper insight into the anisotropic photoelectric properties of Cs3Bi2I9, thus contributing to the development of metal halide perovskites in the field of optoelectronics.

Effect of Deep-Level Defects on the Performance of CdZnTe Photon Counting Detectors.

The effect of deep-level defects is a key issue for the applications of CdZnTe high-flux photon counting devices of X-ray irradiations. However, the major trap energy levels and their quantitive relationship with the device's performance are not yet clearly understood. In this study, a 16-pixel CdZnTe X-ray photon counting detector with a non-uniform counting performance is investigated. The deep-level defect characteristics of each pixel region are analyzed by the current-voltage curves (I-V), infrared (IR) optical microscope photography, photoluminescence (PL) and thermally stimulated current (TSC) measurements, which indicate that the difference in counting performance is caused by the non-uniformly distributed deep-level defects in the CdZnTe crystals. Based on these results, we conclude that the CdZnTe detectors with a good photon counting performance should have a larger Te cd 2 + and Cd vacancy-related defect concentration and a lower A-center and Tei concentration. We consider the deep hole trap Tei, with the activation energy of 0.638-0.642 eV, to be the key deep-level trap affecting the photon counting performance. In addition, a theoretical model of the native defect reaction is proposed to understand the underlying relationships of resistivity, deep-level defect characteristics and photon counting performance.