Synthesis and characterization of Pr<Superscript>3+</Superscript>-doped glass scintillators prepared by the sol–gel method

Transparent and crack-free Pr-doped silica glass scintillators were successfully synthesized using the sol–gel method. A peak found at 301 nm in the photoluminescence spectrum was ascribed to a radiative transition of the Pr³⁺ emission center. The associated excitation peak was located at 276 nm. The energy of the excitation peak (4.50 eV) was significantly lower than the energy gap (5.83 eV) of the ¹S₀ to ³H₄ f–f transition. Therefore, the f–f transition was excluded as the origin, and the transition was attributed to 5d–4f. In the absorption spectrum, several bands of the f–f transition were observed. Fourier transform infrared spectroscopy was employed to understand the microstructural features and OH group concentration in the Pr³⁺-doped silica glass. It was revealed that a Si–O network had been successfully formed, and that the OH group concentration decreased with increasing thermal treatment temperature reaching a saturation value for temperatures higher than 750 °C. The absence of praseodymium oxide nanocrystalline clusters was confirmed by transmission electron microscopy (TEM), even in the sample with the highest Pr ion concentration. Scintillation properties of the Pr³⁺-doped silica glass were also characterized. The scintillation decay time constants were estimated to be approximately 1.3 and 14 ns, which supports the assignment of the luminescence to the 5d–4f transition. The scintillation light yield of the Pr³⁺-doped silica glass was estimated to be approximately 130 photons/MeV.     

Adsorption behavior of 181W and 93mMo as lighter homologues of seaborgium (Sg) in HF/HNO3 on anion-exchange resin

Adsorption of carrier-free radiotracers ¹⁸¹W and ^93mMo produced in the ¹⁸¹Ta(p, n) and ^natNb(p, n) reactions, respectively, on anion-exchange resin was studied in mixed solution of HF and HNO₃ in a concentration range of 10⁻⁴–10⁻¹ M HF/0.1 M HNO₃. Distribution coefficients (K _d) of ¹⁸¹W and ^93mMo at 70 °C showed the V-shaped variation with the minimum at around 10⁻¹ M HF/0.1 M HNO₃, although variation of the K _d values for ^93mMo was quite small compared with that for ¹⁸¹W. Formation of oxofluoro complexes for W and Mo is briefly discussed.     

Dihydrobenzofurans as cannabinoid receptor ligands from Cordyceps annullata,an entomopathogenic fungus cultivated in the presence of an HDAC inhibitor

The secondary metabolite production of Cordyceps annullata, an entomopathogenic fungus, was clearly enhanced by the addition of suberoyl bis-hydroxamic acid (SBHA), a histone deacetylase (HDAC) inhibitor, to the culture medium. Four new 2,3-dihydrobenzofurans, annullatins A–D (1–4), and a new aromatic polyketide, annullatin E (5) were isolated from the culture medium, and the structures, including the absolute stereochemistries, were determined by spectroscopic analysis, vibrational circular dichroism (VCD), and chemical transformations. Annullatin A (1) exhibited potent agonistic activity toward the cannabinoid receptors CB1 and CB2. Annullatin B (2) and D (4) displayed CB1 agonistic activity and CB2 inverse agonistic activity.     

First observation of o-Ps to p-Ps transition and first direct measurement of positronium hyperfine splitting with sub-THz light

Positronium is an ideal system for the research of the bound state QED. The hyperfine splitting of positronium (Ps-HFS, about 203 GHz) is an important observable but all previous measurements of Ps-HFS had been measured indirectly using Zeeman splitting. There might be the unknown systematic errors on the uniformity of magnetic field. We are trying to measure Ps-HFS directly using sub-THz radiation. We developed an optical system to accumulate high power (about 10 kW) radiation in a Fabry-Pérot resonant cavity and observed the positronium hyperfine transition for the first time.     

Tenuipyrone, a novel skeletal polyketide from the entomopathogenic fungus, Isaria tenuipes, cultivated in the presence of epigenetic modifiers

The concomitant addition of the histone deacetylase inhibitor and the DNA methyltransferase inhibitor to the culture medium of an entomopathogenic fungus, Isaria tenuipes, greatly enhanced its secondary metabolite production and led to the isolation of tenuipyrone (1), a novel polyketide with an unprecedented tetracyclic ring system bearing a spiroketal structural component, along with two known C(10)-polyketides, cephalosporolide B (2), which is a plausible biosynthetic precursor of 1, and cephalosporolide F (3).     

Optical band gap of semiconductive type II Si clathrate purified by centrifugation

The optical properties of Si clathrate, which is believed to have potential as a new Si-based material for optical devices, were investigated in this study. Si clathrates with type II structure (Na_xSi₁₃₆) with low Na content (x = 1.3, 2.0) were synthesized by thermal decomposition of NaSi. The synthesized samples were purified by centrifugation using a solution of CH₂Br₂–C₂Cl₄ to remove impurities. Using the obtained high purity samples (Na_1.3Si₁₃₆, 93 wt.%; Na_2.0Si₁₃₆, 90 wt.%), the optical absorption spectra of Na_xSi₁₃₆ were clarified, for the first time, from diffuse reflection measurements. The inclusion of Na in Si₁₃₆ was found to cause free carrier absorption in the infrared region but had little effect on the fundamental absorption edge found in the visible region.     

A metallofullerene that encapsulates 225Ac

The properties of a metallofullerene that encapsulates ²²⁵Ac were studied by radio-chromatographic methods. The results of chromatography on a Buckyclutcher column suggest that there are some metallofullerene isomers of AcC₈₂. The identical HPLC retention time of the major AcC₈₂ peak with that of La@C₈₂ indicates that the structure of one of the AcC₈₂ isomers is the same as La@C₈₂.     

Optimization of an isothermal gas-chromatographic setup for the chemical exploration of dubnium (Db,Z = 105) oxychlorides

An isothermal gas-chromatographic (IGC) device has been developed and tested for on-line gas phase studies of volatile oxychlorides of short-lived group-5 transition metals. Radioisotopes of niobium and tantalum, produced in nuclear fusion evaporation reactions, are directly flushed into the IGC setup by an inert gas-jet. Oxychloride compounds are formed by the addition of SOCl₂ and O₂. Parameters influencing the formation and transport of NbOCl₃ and TaOCl₃ are discussed. For nuclides with half-lives (t_1/2) of about 30 s, an overall efficiency of 7% is obtained, rendering the IGC setup suitable for the chemical exploration of ²⁶²Db (t_1/2?=?34 s).

     

Onset of pi(0) suppression studied in Cu+Cu collisions at sqrt S NN=22.4, 62.4, and 200 GeV

Neutral pion transverse momentum (p(T)) spectra at midrapidity (|y| less than or approximately 0.35) were measured in Cu+Cu collisions at sqrt[s(NN)]=22.4, 62.4, and 200 GeV. Relative to pi_(0) yields in p+p collisions scaled by the number of inelastic nucleon-nucleon collisions (N(coll) the pi_(0) yields for p(T) more than or approximately 2 GeV/c in central Cu+Cu collisions are suppressed at 62.4 and 200 GeV whereas an enhancement is observed at 22.4 GeV. A comparison with a jet-quenching model suggests that final state parton energy loss dominates in central Cu+Cu collisions at 62.4 and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.