A new hybrid photomultiplier tube as detector for scintillating crystals

In this work, we have attentively studied the performance of a new hybrid photomultiplier tube (HPMT) as detector for photons from scintillating crystals. The HPMT is equipped with a YAP window in order to improve light collection and increase measured light response from scintillating crystals. Several measurements have been performed on BGO, LSO, CsI(Tl) and NaI(Tl) planar crystals having three different surface treatments as well as on YAP : Ce and CsI(Tl) matrices. Such crystals have been coupled to two HPMTs, one equipped with a YAP window (Y-HPMT) and the other with a conventional quartz window (Q-HPMT). Measurements on crystals coupled to the Y-HPMT have shown a consistent improvement of the light response, thanks to the presence of the YAP window. Indeed, the light response measured with the Y-HPMT was on average equal to 1.5, 2.1 and 2.6 times that obtained with the Q-HPMT for planar crystals with white painted (diffusive), fine ground and polished rear surfaces, respectively. With regards to crystal matrices, we measured a light response increase of about 1.2 times.     

Systematic studies of scintillation detector with timing resolution of 10 ps for heavy ion beam

We have tested Time-Of-Flight detectors consisting of several combinations of scintillators and photomultiplier tubes for the identification of produced heavy ion beam. Timing resolution of 6.8 ps (RMS) is achieved with energy deposited of 150–160 MeV in the plastic scintillator, where ⁴⁰Ar beam is used as a primary beam at the total energies of 3.8 GeV. Our systematic studies suggest the importance of maximizing the number of photoelectrons, where the timing resolution seems to be scaled by the pulse height according to the characteristic function of the photomultiplier tube. In addition, scintillator with faster timing property seems to be also essential for better timing resolution.     

Development of the tandem reciprocating magnetic regenerative refrigerator and numerical simulation for the dead volume effect

In this paper, the development of the tandem reciprocating room-temperature active magnetic regenerative refrigerator and the numerical simulation for the effect of the dead volume are presented. The dead volume effect is analyzed by establishing a one-dimensional time-dependent model for the active magnetic regenerator (AMR). The cooling power at the mass flow rate of 5 g s⁻¹ water and a temperature span of 20 K is reduced from 4 W to 2 W when the length of the dead volume (D_DV = 12 mm) is increased from 15 mm to 30 mm. The numerical results indicate that the minimization of dead volume facilitates the improvement of the AMR performance. In particular, the components and the parameters of AMR system are demonstrated. The printed circuit heat exchangers (PCHEs) are employed as the warm end heat exchangers in order to minimize the dead volume of the system. The experimental apparatus includes two active magnetic regenerators containing 186 g of Gd spheres. The maximum no-load temperature span of 26.8 K and a maximum cooling power of 33 W at a zero temperature span were obtained with the frequency of 0.5 Hz under the maximum field of 1.4 T.     

A new inexpensive method for the preparation of acicular precursors for magnetic recording media

Magnetic materials meant for audio/video recording applications necessitate that polycrystalline materials be in acicular shape. So preparation of acicular precursors for magnetic storage materials assumes significance. The employment of aqueous solutions do not produce needle shape crystallites. Glycerol is one of the complexing media used for the precipitation of ferrous oxalate dihydrate. An inexpensive method using starch for preparation of acicular particles is described. The influence of an additive namely Gd on acicularity is also investigated.     

Effect of citric acid content on the structural and magnetic properties of SrFe12O19 thin films

Strontium hexaferrite SrFe₁₂O₁₉ thin films have been synthesized on the Si (100) substrate using spin coating sol-gel process. The influence of different citric acid to metal ions (CA/MN) molar ratios of 0.5, 1 and 1.5 on the formation of SrFe₁₂O₁₉ was investigated. Fourier transform infrared analysis and theoretical calculations were conducted to determine and help control the concentration of metal citrates in solution precursors. X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer techniques were also applied to evaluate the composition, microstructure, crystallite size and magnetic properties of the SrFe₁₂O₁₉ thin films. The results showed that single phase strontium hexaferrite thin films with optimum physical properties can be obtained from the solution with the CA/MN molar ratio of 1 after calcination at 800 °C. The SrFe₁₂O₁₉ thin films synthesized with the CA/MN molar ratio of 1 exhibited crystallite size of 42 nm and isotropically magnetic properties of M_s = 267.5 kA/m (at 795.8 kA/m), M_r = 134 kA/m, and H_c = 341.4 kA/m.     

Enhancement of the magnetic properties of Ni-Cu-Zn ferrites with the substitution of a small fraction of lanthanum for iron

The effect of lanthanum ion substitution for iron on the structural and magnetic properties of Ni-Cu-Zn ferrite is reported. The (Ni_0.25Cu_0.20Zn_0.55)La_xFe_2−xO₄ ferrite compositions with x = 0.0, 0.025, 0.050 and 0.075, were synthesized by nitrate-citrate auto-combustion route. Rietveld structure refinement was carried out to evaluate; La solubility in spinel, residual stress in sintered core, quantity of secondary LaFeO₃ phase formed and change in lattice parameters, etc. Density, crystallite size, grain size, residual macrostress and initial permeability were directly affected by the substitution. A significant increase in initial permeability was achieved by a small fraction of La substitution. The La solubility in the Ni-Cu-Zn ferrite lattice was found very low (∼0.1 atom/unit cell). Co-relations between magnetic properties and measured physical/structural properties were discussed.     

Optimization of magnetic field configuration for the production of Ar ions from RIKEN 18 GHz ECR ion source

We successfully extracted a 1.9 mAAr⁸⁺ ion beam and a 1 mAAr⁹⁺ ion beam from the RIKEN 18 GHz ECR ion source at the extraction voltage of 17 kV and the microwave power of 700–800 W. To obtain these intensities, we optimized the magnetic field configuration and the plasma electrode position.     

Axial crushing of tubes as an energy dissipating mechanism for the reduction of acceleration induced injuries from mine blasts underneath infantry vehicles

A novel simple numerical formulation has been developed and implemented as a program to improve the capability of analytical approaches while reducing the dependence on computationally intensive numerical simulations. The formulation is based on an energy balance approach and utilizes explicit time integration of governing analytical energy equations to study the plastic work of the tube and impactor velocity in real time. An impulse–momentum equation yields the time history of the dynamic axial crushing force. The results of the numerical formulation are in excellent agreement with data from various external sources. The geometric and material properties of the tube can be varied to accurately study their effect on the dynamic crushing response, thus eliminating the need for frequent destructive testing. Further, the numerical formulation when properly modified, can predict occupant responses such as lumbar accelerations and compressive forces when used in crashworthiness applications.     

A simple model for falling film absorption on vertical tubes in the presence of non-absorbables

Most water–lithium bromide (LiBr) absorption chillers have a purge system to remove non-absorbable gases that cause a reduction in cooling capacity. Generally, the non-absorbables are originated in corrosion/passivation processes inside the machine, but leaks can also be a source of concern. However, since leaks must be corrected immediately to avoid machine deterioration, this study is mostly aimed at the non-absorbables evolved during operation. This paper analyses the effect of inlet non-absorbable air concentration, outlet purge velocity, absorber pressure and cooling water temperature on the falling film absorption process inside a vertical tube absorber, based on a simple transport coefficient model. This model consists of three ordinary differential equations solved with as method for initial-value problem, and a set of auxiliary equations. The study shows that the effect of non-absorbables can be significant, and furthermore provides a quantitative framework to aid in purge design. The nominal working conditions in this study were a solution Reynolds number of 100, an absorber pressure of 1.3 kPa, a cooling water temperature of 35 °C and an inlet solution concentration of 62% LiBr by weight. The results indicate that a minimum vapour velocity is required to sweep the non-absorbables along the absorber towards the purge, thus preventing reduced absorption fluxes. At a cooling water temperature of 35 °C, an inlet air concentration of 20% (by mole) resulted in a 61% reduction in mass absorption flux.     

New heat generation material in AC magnetic field for Y3Fe5O12-based powder material synthesized by reverse coprecipitation method

We found the most promising powder material for the application of the thermal coagulation therapy for the treatment of cancerous tissues. The maximum heat generation ability (ΔT = 40-77 °C, 370 kHz, 1.77 kA·m^− 1) was obtained for the powder materials by the calcination at 1100 °C for the Y_3 − XGd_XFe₅O₁₂ system. This ΔT value is higher than ca. ΔT = 30 °C in same magnetic field for fine FeFe₂O₄ particles as the candidate material for this type of therapy. The particle growth with the formation of the cubic single phase might influence to the high heat generation. As an unexpected result, the Gd₃Fe₅O₁₂ (X = 3) has no heat generation ability in an AC magnetic field.     

Sr and Ba substitution in charge ordered Pr0.5Ca0.5MnO3: Sharp steps in the magnetic and transport properties for a narrow composition range

The magnetic and transport properties of Pr_0.5Ca_0.5−xA_xMnO₃ (A = Sr, Ba) have been investigated in this paper. The substitution of Ca with bigger cations such as Sr and Ba can favour the field-induced ferromagnetism and induce sharp steps in the magnetization versus field and resistivity versus field curves. These properties strongly depend on the thermal history of the samples. All the results have been interpreted by a martensitic-like mechanism based on phase separation induced by A-site size mismatch. The above model can also explain the result that the less efficient ability of Sr substitution than Ba substitution to induce ferromagnetism and sharp steps. Another interesting feature in the system is the existence of an optimum substitution range to induce magnetization steps and reach high field-induced magnetization values for both Sr (x = 0.07–0.10) and Ba (x = 0.01–0.08) substitution. We suggest that the disappearance of the steps beyond the optimum substitution range possibly results from the different nature of phase separation in the optimum substitution range and beyond this range.     

Modeling of the interface behavior in tape casting of functionally graded ceramics for magnetic refrigeration parts

The main goal of this work is to study the multiple material flows in side-by-side (SBS) tape casting and analyze the influence of the different material properties, i.e. the density and the viscosity, on the interface between the fluids, since this is highly important for the efficiency of a graded configuration of the magnetocaloric materials. The Newtonian flow behavior with relatively high viscosity is assumed for each fluid and used in the simulation with a commercial CFD code (ANSYS FLUENT). The results show that the density difference does not affect the interface between the adjacent fluids, whereas the viscosity of the fluids plays the most important role in the behavior of the interface. Moreover, increasing the viscosity difference of the adjacent fluids, Δμ, leads to increasing the diffusive region between them. However, this can be counteracted by decreasing the velocity by the substrate.     

Application of Box–Behnken design in the optimization of a magnetic nanoparticle procedure for zinc determination in analytical samples by inductively coupled plasma optical emission spectrometry

This article describes the development of a procedure for zinc determination in water and biological samples after extraction by magnetic nanoparticles by inductively coupled plasma optical emission spectrometry (ICP-OES). The optimization strategy was carried out by using two level full factorial designs. Results of the two level full factorial design (2⁴) based on an analysis of variance demonstrated that only the pH, amount of extractant and amount of nanoparticles were statistically significant. Optimal conditions for three variables: pH of solution, amount of extractant (E), and amount of nanoparticles (N) for the extraction of zinc samples were obtained by using Box–Behnken design. These values were 3.8, 3.1 and 3.3 mg, for pH of solution, amount of nanoparticles and amount of extractant, respectively. Under the optimized experimental conditions, the detection limit of the proposed method followed by ICP-OES was found to be 0.8 μg L⁻¹. The method was applied to the determination of zinc in water and biological samples.     

Structural characterization, thermal, spectroscopic and magnetic studies of the (C3H12N2)0.75[Mn1.50Fe1.50(AsO4)F6] and (C3H12N2)0.75[Co1.50Fe1.50(AsO4)F6] compounds

The (C₃H₁₂N₂)_0.94[Mn_1.50Fe_1.50^III(AsO₄)F₆] and (C₃H₁₂N₂)_0.75[Co_1.50Fe_1.50^III(AsO₄)F₆] compounds 1 and 2 have been synthesized using mild hydrothermal conditions. These phases are isostructural with (C₃H₁₂N₂)_0.75[Fe_1.5^IIFe_1.5^III(AsO₄)F₆]. The compounds crystallize in the orthorhombic Imam space group. The unit cell parameters calculated by using the patterns matching routine of the FULPROOF program, starting from the cell parameters of the iron(II),(III) phase, are: a = 7.727(1) Å, b = 11.047(1) Å, c = 13.412(1) Å for 1 and a = 7.560(1) Å, b = 11.012(1) Å, c = 13.206(1) Å for 2, being Z = 8 in both compounds. The crystal structure consists of a three-dimensional framework constructed from edge-sharing [M^II(1)₂O₂F₈] (M = Mn, Co) dimeric octahedra linked to [Fe^III(2)O₂F₄] octahedra through the F(1) anions and to the [AsO₄] tetrahedra by the O(1) vertex. This network gives rise two kinds of chains, which are extended in perpendicular directions. Chain 1 is extended along the a-axis and chain 2 runs along the c-axis. These chains are linked by the F(1) and O(1) atoms and establish cavities delimited by eight or six polyhedra along the [1 0 0] and [0 0 1] directions, respectively. The propanediammonium cations are located inside these cavities. The thermal study indicates that the structures collapse with the calcination of the organic dication at 255 and 285 °C for 1 and 2, respectively. The Mössbauer spectra in the paramagnetic state indicate the existence of two crystallographically independent positions for the iron(III) cations and a small proportion of this cation in the positions of the divalent Mn(II) and Co(II) ones. The IR spectrum shows the protonated bands of the H₂N- groups of the propanediamine molecule and the characteristic bands of the [AsO₄]³⁻ arsenate oxoanions. In the diffuse reflectance spectra, it can be observed the bands characteristic of trivalent iron(III) cation and divalent Mn(II) and Co(II) ones in a distorted octahedral symmetry. The calculated Dq and B-Racah parameters for the cobalt(II) phase are 710 and 925 cm⁻¹, respectively. The ESR spectra of compound 1 maintain isotropic with variation in temperature, being g = 1.99. Magnetic measurements for both compounds indicate that the main magnetic interactions are antiferromagnetic in nature. However, at low temperatures small ferromagnetic components are detected, which are probably due to a spin decompensation of the two different metallic cations. The hysteresis loops give values of the remnant magnetization and coercive field of 84.5, 255 emu/mol and 0.01, 0.225 T for phases 1 and 2, respectively.