CsI Matrix Research Articles

Green, solventless debromination of C70Br10 to C70 with CsI

A smooth, solventless and solid state debromination of C70Br10 can be achieved in a CsI matrix with the restoration of the pristine C70 in quantitative yields. Such debromination reaction was studied with FT-IR spectroscopy and its kinetics was fitted by a pseudofirst order law, with a rate constant in the range of 3.6-5.2 x 10−5 s−1. The thermal properties of the compound C70Br10 were studied with TGA and DSC analysis focusing on the thermal decomposition processes. From the DSC data both the activation energy for the thermal decomposition of C70Br10 as well as its enthalpy of formation were determined. Some considerations on the relative weakness of C-Br bonds in brominated fullerenes compounds were made. Accordingly, the debromination mechanism is discussed in terms of unimolecular elimination reaction (E1) in a concerted mechanism which leads to the restoration of the pristine C70 fullerene.

Green, solventless debromination of C70Br10 To C70 with CsI

A smooth, solventless and solid state debromination of C70Br10 can be achieved in a CsI matrix with quantitative restoration of the pristine C70 in quantitative yields. The debromination kinetics was studied with FT-IR spectroscopy and according to the pseudofirst order kinetics law, the rate constant was found in the range 3.6–5.2 × 10−5 s−1. The compound C70Br10 was studied with TGA and its thermal decomposition by DSC analysis. From the DSC data both the activation energy for the thermal decomposition of C70Br10 was determined as well as its enthalpy of formation, which has led to some considerations on the relative weakness of C–Br bonds in brominated fullerenes compounds. The debromination mechanism is discussed in terms of unimolecular elimination reaction (E1) in a concerted mechanism which leads to the restoration of the pristine C70 fullerene.

SCINTILLATION CHARACTERISTICS OF HEAVILY DOPED CsI:Tl, IO3 CRYSTALS

The effect of 3 IO− ions on spectrometric characteristic of CsI:Tl crystal has been considered. It has been shown that co-doping of CsI:Tl crystal by 3 IO− anions permits to obtain clear ingots with increased thallium concentration up to CTl ~ 0.9 mole % in which the concentration quenching of photo- or radioluminescence do not observed. It has been shown that the decay of solid solution in CsI:Tl, 3 IO crystals is not observed, at least up to CTl ~ 0.5 mole %, as evidenced by a good energy resolution (R = 6.3%) of samples with the specified Tl concentration and this also evidenced by a larger segregation coefficient of thallium in CsI:Tl, 3 IO crystals (k = 0.24 contrary to k = 0.19 in CsI:Tl). An explanation of thallium solid solution stability in CsI matrix has been proposed which based on experimental fact of complex formation. Compensation of elastic stresses of opposite sign due to complex formation results in preventing of nucleation for solid solution decay.

Characteristics of Pb2+ doped CsI matriz under gamma and neutron excitations

In recent years, there has been an increasing interest in finding new fast scintillating material or improve the characteristics of known scintillators for the demand of high energy physics, industrial and nuclear medical applications. Ions divalent lead Pb2 + built in some crystal structures are efficient emission centers and their applications in scintillators was and still is the reason of an intensive study of emission properties of different compounds containing these ions. In this context, the crystals of Pb2 + doped CsI matrix were grown by the vertical Bridgman technique and subjected to annealing in vacuum of 10 -6 mbar and continuous temperatura of 350°C, for 24 hours, and then they were employed. To evaluate the response of the CsI:Pb scintillator crystal to gamma radiation, radioactive sources of 137 Cs (662 keV), 60 Co (1173 keV and 1333 keV), 22 Na (511 keV and 1275 keV) and 133 Ba (355 keV) was used. The operating voltage of the photomultiplier was 2700 V for the detection of gamma rays and the accumulation time in the counting process was 600 s. The scintillator response to neutron radiation from a radioactive source of Am/Be with energy range of 1 MeV to 12 MeV was available. The activity of the AmBe source was 1Ci Am. The fluency was 2.6 x 10 6 neutrons / second. The operating voltage of the photomultiplier tube was 1300 V. The accumulation time in the counting process was 600 s. With the results obtained, it may be observed that the crystals are sensitive to these radiations.

Phase-separated CsI–NaCl scintillator grown by the Czochralski method

A phase-separated CsI–NaCl scintillator with light-guiding properties was grown by the Czochralski method. The CsI–NaCl eutectic phase usually consists of NaCl cylinders in a CsI matrix and contains grain boundaries. However, we have grown composites without grain boundaries by creating a convex solid/liquid interface, selecting a single grain by Dash’s neck method, and increasing the diameter of the composite moderately. The good continuous convection flow required for these conditions was achieved by suppressing the drop in the aspect ratio of the melt height to the crucible radius with a double crucible setup. We successfully obtained a CsI–NaCl:Tl composite that was uniform with no grain boundaries greater than 30mm in diameter.

Luminescent properties of BaCl2-Eu microcrystals embedded in a CsI matrix

The spectral-luminescent properties of CsI-BaCl2(1 mol%)-Eu(0.02 mol%) crystalline system are studied. Europium ion doped BaCl2 microcrystals embedded in a CsI matrix are revealed on CsI-BaCl2(1 mol%)-Eu(0.02 mol%) freshly cleaved surface by the scanning electron microscopy. The size of microcrystals is shown to be within 0.5–5 microns. The luminescent parameters of the BaCl2-Eu2+ microcrystals are shown to be similar to ones of a single crystal analogue. The 4f → 5d absorption transitions in europium ions and the reabsorption of the intrinsic emission of the CsI host are the main excitation mechanisms of europium luminescence in the BaCl2 microcrystals.

Phase-Separated CsI-NaCl Scintillator With Optical Guiding Function

We demonstrate a new scintillator material that has a one-dimensional eutectic structure and optical light-guiding properties. Our light propagation calculations predicted that a structure where high refractive index luminescence cylinders are embedded in a matrix should show effective light-guiding properties. An inverse structure where a high refractive index luminescence matrix contains low refractive index cylinders was also predicted to possess light-guiding properties. A CsI-NaCl:Tl eutectic phase, which contained NaCl cylinders in a CsI matrix, was grown by a one-dimensional solidification method. This material showed high spatial resolution because of the difference in the refractive indices of NaCl and CsI.

In vitro study of the SBF and osteoblast-like cells on hydroxyapatite/chitosan–silica nanocomposite

Hydroxyapatite/chitosan–silica (HApCSi) nanocomposites were synthesized by co-precipitated method and their potential application as filler materials for bone regeneration were investigated in simulated body fluid (SBF). To study their biocompatibility, they were cultured with rat osteoblast-like UMR-106 cells for 3, 7, 14, and 21days. Studies of the silica contents in chitosan matrix showed the presence of silinol (Si–OH) groups in CSi hybrid and their decrease after being composited with calcium phosphate (CaP) which is desirable for the formation of the apatite. XRD and TEM studies showed that the HAp formed in the CSi matrix were nanometer (20–40nm) in size. Nanocomposites of HApCSi20 processed with 20%v/v silica whisker showed a micro hardness of 84.7±3.3MPa. Mineralization study in SBF showed the formation of apatite crystals on the HApCSi surface after being incubated for 7days. In vitro biocompatibility, cell morphology, proliferation, and cell adhesion tests confirmed the osteoblast attachment and growth on the HApCSi20 surface. The density of cells and the production of calcium nodules on the substrate were seen to increase with increasing cultured time. The mechanical evaluation and in vitro experiment suggested that the use of HApCSi composite will lead to the formation of new apatite particles and thus be a potential implant material.

Preliminary study of metabolic radiotherapy with 188Re via small animal imaging

188Re is a β − ( Emax = 2.12 MeV ) and γ (155 keV) emitter. Since its chemistry is similar to that of the largely employed tracer, 99mTc, molecules of hyaluronic acid (HA) have been labelled with 188Re to produce a target specific radiopharmaceutical. The radiolabeled compound, i.v. injected in healthy mice, is able to accumulate into the liver after a few minutes. To study the effect of metabolic radiotherapy in mice, we have built a small gamma camera based on a matrix of YAP:Ce crystals, with 0.6 × 0.6 × 10 mm 3 pixels, read out by a R2486 Hamamatsu PSPMT. A high-sensitivity 20 mm thick lead parallel-hole collimator, with hole diameter 1.5 mm and septa of 0.18 mm, is placed in front of the YAP matrix. Preliminary results obtained with various phantoms containing a solution of 188Re and with C57 black mice injected with the 188Re-HA solution are presented. To increase the space resolution and to obtain two orthogonal projections simultaneously we are building in parallel two new cameras to be positioned at 90 degrees. They use a CsI(Tl) matrix with 1 × 1 × 5 mm 3 pixels read out by H8500 Hamamatsu Flat panel PMT.

Luminescence of Pb2+-based aggregates in CsI matrix

Emission bands at 355, 430, 465, 530, 590 and 730 nm are observed in CsI: Pb system, after annealing at 220–370°C for 20h. Their relative intensities depend strongly on annealing temperature. Absorption and excitation spectra of 465–590 nm emissions have maxima near 410 nm, i.e. in the region of exciton absorption band of bulk CsPbI3. Thus the creation of CsPbI3-like aggregates in CsI matrix is not excluded. The origin of the emission bands and creation mechanism of CsPbI3 aggregates are discussed.

Crystals and light collection in nuclear medicine

Recently, particular attention has been paid to the development of small Field of View (FOV) breast imagers for Nuclear Medicine applications provided with YAP:Ce and CsI, both thallium and sodium doped, multipillar matrices. In order to improve their energy and spatial resolution performances, it is necessary to increase the light output of such scintillating matrices. We have developed a MonteCarlo code with the purpose of studying the detection efficiency as well as the light collection efficiency of crystal pillars as a function of their geometry and surfaces treatment. By analysing both the experimental and the simulations results, we have found out that the best choice for this gamma detector is represented by a CsI(Na) matrix made up of orthogonally arranged pillars whose dimensions are 2×2×3 mm 3. For this geometry, our simulations have showed a detection efficiency of 62%, a collection efficiency of 80% and an expected light output of 68%.

Design features and performance of a CsI(Na) array based gamma camera for small animal gene research

The authors report on the development of a radiation imaging system based on a matrix of CsI(Na) scintillating crystals. This detector system has been optimized for high resolution radiation imaging of the distribution of iodine 125 (/sup 125/I) in a laboratory animal. The radioisotope /sup 125/I is readily available as a label to molecular biology probes that can be used in gene research. Iodine 125 decays via electron capture emitting a 35 keV gamma-ray with the prompt emission of several 27-32 keV X-rays. A coincidence condition can be set to detect the /sup 125/I decays thus reducing background radiation contribution to the image. The system utilizes the Hamamatsu 5 inch diameter 3292 position sensitive photomultiplier tube (PSPMT) coupled to the CsI(Na) matrix and a custom built high resolution copper-beryllium collimator. A conventional photomultiplier coupled to a NaI(Ti) crystal scintillator is used to detect the coincident radiation resulting from the decay of /sup 125/I.

Comparison between YAP : Ce and CsI(Tl) multipillar matrices

The characteristics of segmented CsI(Tl) and YAP : Ce scintillators coupled to a position-sensitive photomultiplier tube (PSPMT Hamamatsu R2486) have been measured and compared to evaluate the potential use of such scintillators as precise X- and γ-ray imagers. For such configurations, we obtained good spatial resolution and linearity over their entire 40×40 mm 2 Fields of View (FOVs). The scintillating matrices consist of orthogonal arrays of crystal pillars with 0.6×0.6 mm 2 cross sections and thicknesses of 3 and 10 mm. The 3 mm thick CsI(Tl) matrix shows a light yield of 44% compared to NaI(Tl), an energy resolution of 22% FWHM at 122 keV, a single pillar spatial response of 0.5 mm FWHM, and a spatial resolution of 0.83 mm.

Are there Diagnostic Spectral Features of Irradiated Cometary Ices?

There is now evidence that at least some cometary nuclei are dark and red. Cometary ices prepared from combinations of CH4 with H2O and sometimes NH3 were irradiated at 77 K by corona discharge. CH4 - containing ice reddened and darkened at a dose ~1011 erg cm−2 over a period of ~1 hour. Upon evaporation of the now yellowish, irradiated ice, a slightly yellowish colored solid film remains on the walls of the container at room temperature. Transmission measurements of this organic film (called cometary tholin) were made from 0.2 μm to 50 μm wavelength. Strong UV absorption is seen from 0.45 μm to 0.2 μm. Above 0.45 μm, the spectrum remains flat to ~1.3 μm in the near infrared, except for a very small feature near 1.15 μm. A medium sized feature appears centered at 1.4 μm with shoulders at both sides and a nearby weaker feature at 1.52 μm. A strong feature appears at 1.9 μm accompanied by a smaller feature at 1.78 μm. in the region 2.5 μm to 50 μm, the infrared spectrum was taken by dispersing the film in a CsI matrix. Bands are found at 2.92(M), 3.36(S), 3.40(S), 3.46(M), 3.48(M), 5.75(M), 5.99(S), 6.21(M), 6.83(M), 7.30(S), 7.81(W), 8.89(M), 9.26(M), 20.00(W), 22.22(W), and 28.57(W) micrometers, suggesting complex organics including alkane, alkene, aldehyde, and carboxylic acid functional groups. These results are also relevant to UV and cosmic ray processing of interstellar grains, and to icy bodies in the outer solar system.

Infrared Spectra of Sodium Salts in CsCl Disks

The use of CsCl as a matrix for the preparation of disks for infrared spectra of sodium salts was investigated. During the grinding of the disks, sodium salts form a substitutional solid solution of hydrated Na+ in a CsCl lattice. The IR spectrum of the substitutional hydrated solid solution has four characteristic HOH absorption bands which are very sharp, whereas in general, the spectra of hygroscopic salts have broad HOH absorption bands. The spectra of sodium salts in a CsCl matrix were compared to those of (1) potassium halides and LiCl in KBr, CsCl, and CsI matrices; (2) various cesium salts in NaCl and NaBr matrices; (3) various sodium salts in a CsI matrix. From the various spectra it was concluded that the formation of the substitutional solid solution of hydrated Na+ in CsCl crystals is a mechanochemical process. In the first step, NaCl is formed because of a double decomposition reaction between the sodium salt and CsCl. In the second step, a solid solution of NaCl in CsCl crystals is obtained because of a mechanochemical process in which planes of NaCl crystals and atmospheric water combine with planes or fractures of CsCl crystals due to sliding of crystal planes under the effect of shearing. Substitutional solid solutions of hydrated Na+ in CsBr and CsI are obtained when NaBr or NaI is ground with CsBr or CsI.

Resonance Raman spectra of Cu‐porphin‐d4(meso) and Ni‐porphin, and the infrared spectrum of Cu‐porphin‐d4

AbstractThe resonance Raman spectra are presented for Ni‐porphin and Cu‐porphin‐d4(meso) as dilute solutions in CS2 and C2Cl4 using an Ar+ laser and a tunable Rhodamine 6G dye laser. The Raman features are assigned to the different vibrational species on the basis of their depolarization data. The assignment of 14 features in the spectrum of Cu‐porphin‐d4 and 13 features in the spectrum of Cu‐porphin and Ni‐porphin is discussed by comparing the spectra of the three molecules. Also the infrared spectrum of Cu‐porphin‐d4 as a solid dispersed in CsI matrix is reported for the 200–2000 cm−1 region.