New fast organic scintillators using intramolecular bromine quenching

Femtosecond laser-induced optical kerr dynamics in CS 2/alkane binary solutions

SynopsisTheoretical and experimental studies have been made of the scintillation pulse shapes of organic scintillators. In a unitary crystal the pulse shape is characterised by the scintillation decay timeτs. In solution scintillators additional parameters are required to describe the pulse shape: Δt, the pulse width (FWHM);tm, the time at which the intensity reaches a maximumpmax; andt½, the time at which the intensity reaches ½pmax. General relations are derived for τs, Δτ,τm,τ½, andpmaxfor binary liquid solutions in terms of molecular parameters, and the corresponding expression is given for the scintillation pulse shape of a binary plastic solution.The scintillation pulse shapes of 4 binary liquid solutions and 12 binary and 15 ternary plastic solutions were measured using a single-photon sampling fluorometer. The results confirm the theoretical analysis. A new plastic scintillator (NE 111) with improved timing characteristics has thus been developed, and some of its applications in nuclear physics are briefly discussed. The time association of nuclear events can be measured to within 130 ps with this scintillator, the limiting factor being the time jitter of the photomultiplier itself.

The green-emitting plastic scintillators with high transparence, short decay time and high quantum yield were fabricated by the modified thermal polymerization procedure. The effects of different concentrations of primary and secondary fluorescent dopants on photoluminescence performance, such as fluorescence intensity, decay time and absolute quantum yield, were investigated through orthogonal experiments. The optimal formula ratio for the plastic scintillator was that the primary dopant concentration was 0.25 wt.% and the secondary dopant concentration was 0.03 wt.%. The photoluminescence decay time of the optimal sample was 3.37 ns, which was faster than that of EJ-260 (6.57 ns) and its corresponding quantum yield was 91.57%, compared to that of EJ-260 (98.59%).

A new technique for measuring the Fickian diffusion coefficient in binary liquid solutions

The behaviour of isotope tracers in diffusion processes was investigated. In systems of organic binary solutions gradients of chemical concentration were present. Using the capillary method the tracer and the mutual diffusion coefficients were determined. It was found that the tracer diffusion coefficient is equal to the mutual one if the tracer moves in the same directions as the unlabelled part of component and the ratio of both parts of component is time independent. When both conditions are not justified the tracer diffusion is due to the simultaneously mutual and self‐diffusion processes.

The properties of high rare-earth-containing borosilicate glasses have been investigated to assess the potential for using these materials to construct electromagnetic calorimeters for particle physics. We report here on measurements of scintillation yield, transmission and decay time, on large blocks of Ce3+-doped Gd2O3-based glasses. The samples were excited by a high energy X-ray beam and the associated scintillation yield and decay time was measured. The optical transmission of the samples was measured. It was observed that scintillation yield of present scintillation glass is 20% of BGO scintillation yield, decay time is in range of 50 - 80 ns, glass density is 5.50 g/cm3. It was concluded that higher light yield and density make this glass become promising candidate for cerium doped dense glass scintillator.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Digital Light Processing (DLP) 3D printing technique can be a powerful tool to fabricate plastic scintillator with a geometrically desired shape in innovatively fast time. Plastic scintillator with the size of 30 mm × 30 mm × 10 mm was fabricated by using the plastic resin and the DLP 3D printer (ASIGA, Pico2HD). The characteristics of decay time, energy resolution, intrinsic detection efficiency were analyzed and compared between the fabricated 3D printing plastic scintillator and a commercial plastic scintillator BC408 (Saint-Gobain Crystal). Decay time profile of the tested plastic scintillators was measured for 137Cs Compton maximum electron 477 keV by using a modified time correlated single photon counting (TCSPC) setup. The time profile was fitted by reconvolution function, and each decay time component and contribution was analyzed. For energy resolution of plastic scintillator, the Gaussian spectrum for 137Cs Compton maximum electron 477 keV was selectively measured by using the γ-γ coincidence experimental setup. As a result, it was confirmed that the 3D printing plastic scintillator showed average decay time 15.6 ns and energy resolution 15.4%. These characteristics demonstrates the feasibility of 3D printing plastic scintillator as a radiation detector.

Molecular interaction forces in acetone + ethanol binary liquid solutions: FTIR and theoretical studies

Binary and ternary transition metal dichalcogenide (TMD) heterostructures, MSe2 and MSeS (where M = Mo or W), are investigated as future building blocks for high‐performance device applications with a tailorable electronic bandgap. For light‐emitting device applications, investigating the decay time of the material is a prerequisite. Herein, time‐resolved photoluminescence (TRPL) of binary and ternary TMD heterostructures is measured. A tri‐exponential function is adopted to fit the TRPL data. Short, medium, and long decay times are <50 ps, ≈400 ps, and >400 ps, respectively. Except for monolayer MoSe2 and MoSeS, only two PL decay time components are observed with a large contribution from short decay time photocarriers (>80%). Bilayer TMDs exhibit a much shorter PL decay time, which could be attributed to the indirect nature of excitons and different dielectric environments, compared with that of monolayer TMDs. Using the center‐of‐mass (CM) method, a PL decay time map is successfully obtained for binary and ternary TMD heterostructures. This allows the qualitative visualization of the decay time distribution within the heterostructure or among other materials. This technique could be applied to assess the decay time of materials used in high‐performance light‐emitting devices.

Poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) exhibits two distinct conformations in solution depending on the temperature and solvent. The transition from the high- to low-temperature conformation resembles the β-phase formation of poly(9,9-dioctylfluorene) (PFO), in the sense that there is an increase of the conjugation length, while involving less pronounced enthalpy and entropy changes (ΔH = −7.1 kcal/mol and ΔS = −22.9 cal/(mol K) vs ΔH = −18.0 kcal/mol and ΔS = −68.4 cal/(mol K) for PFO). The entropy loss indicates a substantial increase in the polymer order in the low-temperature conformation. Fluorescence decays of F8T2 in solvents with various viscosities, at different temperatures and collected at different emission wavelengths, are triple-exponential in character (e.g., 20, 440, and 650 ps in methylcyclohexane, at 20 °C). The two longer decay times are related to the lifetimes of the two conformations. The shorter decay time appears as either a decay or rise time, at the onset or the tail of the emission band, respectively, and is assigned to conformational relaxation on the basis of its dependence on solvent viscosity and temperature.

In this study, simultaneous adsorption of cationic dyes was investigated by using binary component solutions. Thiourea-modified poly(acrylonitrile-co-acrylic acid) (TMPAA) polymer was used as an adsorbent for uptake of cationic dyes (malachite green, MG and methylene blue, MB) from aqueous solution in a binary system. Adsorption tests revealed that TMPAA presented high adsorption of MG and MB at higher pH and higher dye concentrations. It suggested that there are strong electrostatic attractions between the surface functional groups of the adsorbent and cationic dyes. The equilibrium analyses explain that both extended Langmuir and extended models are suitable for the description of adsorption data in the binary system. An antagonistic effect was found, probably due to triangular (MG) and linear (MB) molecular structures that mutually hinder the adsorption of both dyes on TMPAA. Besides, the kinetic studies for sorption of MG and MB dyes onto adsorbent were better represented by a pseudo-second-order model, which demonstrates chemisorption between the polymeric TMPAA adsorbent and dye molecules. According to experimental findings, TMPAA is an attractive adsorbent for treatment of wastewater containing multiple cationic dyes.

Development of a single crystal with a high index of refraction

Si/β-FeSi2 particles/Si(001) and Si/β-FeSi2 film/Si(111) structures were grown by reactive deposition epitaxy (RDE) and by molecular beam epitaxy (MBE), and time-resolved photoluminescence (PL) was measured from 8 K to 150 K. Both samples exhibited the same PL peak wavelength of 1.54 µm at low temperatures, but the PL decay time of 1.54 µm emission was different, showing that the luminescence originated from different sources. A short decay time (τ∼10 ns) was found to be dominant for the Si/β-FeSi2 particles/Si(001) at low temperatures. In contrast, the decay curve of the Si/β-FeSi2 film/Si(111) was well fitted by assuming a two-component model, with a short decay time (τ∼10 ns) and a long decay time (τ∼100 ns).

The structure of diffusion flames burning pure, binary, and ternary solutions of methanol, heptane, and toluene

We have developed a compact, stable, single-stage intensified photodiode array detector for photon-counting, far ultraviolet astronomy applications. The intensifier, constructed by ITT, employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain (≈10⁶) pulses with a narrowly peaked pulse height distribution. A high efficiency, opaque CsI photocathode is coated directly onto the MCP input surface. The P-20 output phosphor exhibits a very short (≈10μs) decay time, due to the high current density of the electron pulses. We are currently coupling this intensifier to a Reticon RL1024-SF self-scanning linear photodiode array, with 1024 - 25μ x 2.5 mm tall diodes. This device has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. Initial testing has been accomplished using the driver circuitry supplied by Reticon, followed by a 4 bit ADC and DMA interface with an HP 9845 desktop computer. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location. Event location algorithms that compute the pulse centroids to 1/2 diode width accuracy have yielded detector spatial resolution limited by the MCP channel spacing (32μ). Designs for a fast amplifier/clock driver circuit and a bit-slice microprocessor device for real-time photon event location are now being implemented. We anticipate that the short phosphor decay time and use of a fast, dedicated microprocessor for event location will permit rapid scan speeds and hence large dynamic range. The small physical size, stability, insensitivity to environment, low bias voltage, wide dynamic range and independent pixel properties combine to make this detector very suitable for space flight astronomy applications.