Test of a micromegas detector with helium-based gas mixtures for active target time projection chambers utilizing radioactive isotope beams

A Micromegas detector was tested in a helium-carbon dioxide mixture at atmospheric pressure. A stable operation of the detector was confirmed at a gain of over 10³ for a standard alpha source of ²⁴¹Am. In order to realize a position-dependent gain, an anode strip was biased while keeping the other strips at the ground potential. The gain of the biased strip was reduced by one order of magnitude without affecting the gains of the neighboring strips. The energy spectra at 3.7 MeV, the energy deposited by Am alpha particles in the sensitive region of the Micromegas, were obtained from the total charge and the charge deposit profile along the track. The energy resolutions for helium:carbon dioxide 90:10 mixture at a gas gain of about 100 were 11% FWHM for the former and 4% FWHM for the latter. The present results highlight the Micromegas as a promising electron amplifier of the forthcoming active target time projection chambers that will be dedicated to nuclear reactions with radioactive isotope beams.     

Growth, thermal and spectroscopic characteristics of LiNd(WO4)2 crystal

Crystal growth, thermal and optical characteristics of LiNd(WO₄)₂ crystal have been investigated. The LiNd(WO₄)₂ crystal up to Ø15 × 32 mm³ has been grown by Czochralski technique. The hardness is about 5.0 Mohs’ scale. The specific heat at 50 °C is 0.42 J g⁻¹ K⁻¹. The thermal expansion coefficient for c- and a- axes is 1.107 × 10⁻⁵ and 2.104 × 10⁻⁵ K⁻¹, respectively. The absorption and fluorescence spectra and the fluorescence decay curve of LiNd(WO₄)₂ crystal were measured at room temperature. Some spectroscopic parameters such as the intensity parameters, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and emission cross sections were estimated.     

Improvement of semiconductor detector characteristics during supercurrent proton irradiation

Volt-ampère characteristics of Si p-type detectors are established to improve after pulse supercurrent irradiation with low energy protons. Appreciable improvement of energy resolution is observed for detectors irradiatied with the supercurrent proton beam within a dose interval from 10¹¹ to 5×10¹² proton cm⁻². Radiational resource of operation increases from 2.3 × 10¹⁰ to 3.7×10 ¹¹ proton cm⁻² for detectors which were pre-irradiated by the supercurrent proton beam.     

Surface and grain-boundary energies as well as surface mass transport in polycrystalline CeO2

The multiphase equilibration technique for the determination of the equilibrium angles that develop at the interphase boundaries of a solid–liquid–vapor system, has been used to calculate the surface and interfacial energies in polycrystalline CeO₂ and CeO₂/Cu system in argon atmosphere at the temperature range 1473–1773 K. Linear temperature functions were obtained by extrapolation, for the surface energy γ_sv (J/m²) = 2.465–0.563 × 10⁻³ T and the grain-boundary energy γ_ss (J/m²) = 1.687–0.391 × 10⁻³ T of the ceramic, as well as for the interfacial energy γ_sl (J/m²) = 2.623–1.389 × 10⁻³(T −1356 K) of the CeO₂/Cu system. Grain-boundary grooving studied on polished surfaces of CeO₂ annealed in argon atmosphere at the same temperature range has shown that surface diffusion was the dominant mechanism for the mass transport. The surface diffusion coefficient can be expressed according to the equation D_s (m²/s) = 3.82 × 10⁻⁴ exp(−308,250/RT).     

A detection system for energetic light heavy ions

A light heavy ion detection system which consists of a gas-filled ionization chamber (IC) connected to a scattering chamber via a time-of-flight (TOF) system has been constructed. The entrance window of the IC has an area of 14 × 40 cm², the active depth is 115 cm. Filled with CF₄ at a pressure of 350 Torr, the energy range for ¹²C and ⁴⁰Ar is 5–20 MeV/A and 6–30 MeV/A, respectively. The TOF system consists of two parallel plate avalanche counters with a flightpath of 70 cm in between. The IC has been tested with ¹²C ions at an energy of 39 MeV. The energy resolution of the IC (1.1%) is mainly determined by the energy straggling in the foils of the TOF system and the ionization chamber. The energy-loss resolution is 3.5%, the horizontal position resolution varies between 6 and 20 mm and the vertical position resolution is 2 mm. The time resolution of the TOF system ranges from 800 ps for ⁴He at 5.0 MeV, to 280 ps for ²⁸Si at 55 MeV.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Growth and optical characterizations of (Ba0.32Sr0.68)5Nb4O15 crystal

(Ba_0.32Sr_0.68)₅Nb₄O₁₅ crystal with sizes of Ø 17 × 35 mm was grown successfully by Czochralski technique method. The thermal anisotropy was discussed. The principal coefficients of thermal expansion along (100), (010), (001) directions were precisely measured to be 1.308 × 10^− 5, 1.288 × 10^− 5, 1.478 × 10^− 5 K^− 1, respectively. Its optical transparency range has been measured and found to span from 323 to 5500 nm. The bands present in the IR spectra were identified and assigned to the corresponding vibration modes of NbO₆ anions.     

Development of a cryogenic gas target for intense RI beam production at CRIB

Nuclear reactions of astrophysical interest, especially those under high-temperature and high-density conditions, require high-intensity low-energy radioactive ion beams, because the cross-sections are very small for the direct method study. Production of high-intensity radioactive ion beams is, therefore, one of the key developments for RI beam facilities.We report the development of a new cryogenic RI beam production gas target, along with its characteristics and performance. Some of its advantages are the increased stability against high-current primary beams and the increased thickness due to the cooling by liquid nitrogen.The target is being tested with heavy-ion beams. Measures by energy loss of the beam indicate that a thickness of about 2.4 mg/cm² of H₂ gas has been attained and a secondary beam of ⁷Be⁴⁺ at 4.0 MeV/u of more than 2×10⁸ pps was produced.     

The performance of thinner-THGEM

A thinner-THGEM (Thick Gas Electron Multiplier) with a thickness of 200 μm and small rim has been produced by high speed drilling and global etching. Some performances have been studied and the working conditions have been tested and selected, using various Ar and Ne based gas mixtures. Gain values above 3×10³ under relatively low working voltage, energy resolution of 15.9% with 5.9 keV X-rays and good gain stability are obtained. Using Monte Carlo simulation, the dependence of the energy resolution on drift electric field was analyzed and compared with experimental results.     

Ion–molecule reactions in mixtures of ethane with carbon tetrafluoride

Ion–molecule reactions have been measured for the ethane–carbon tetrafluoride mixtures of different compositions using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of ethane in these mixtures ranged from 10% to 90% (at 10% increment). The following primary and secondary ions: CH₃⁺, F⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, C₂H₆⁺, C₃H₅⁺, C₃H₇⁺, C₄H₇⁺, C₄H₉⁺, C₄H₁₀⁺, C₄H₁₁⁺ and CF₃⁺ were observed. Relative ion current intensities for primary and secondary ions are presented as a function both of total mixture pressure and concentration of carbon tetrafluoride in the mixture. Primary ions were produced by electrons with the energy of 300 eV. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. The total mixture pressure was changed from 0.7 to 26.6 Pa. Schemes of ion–molecule reactions were proposed.     

Solid–liquid interfacial energy of camphene

The Gibbs–Thomson coefficient and the solid–liquid interfacial energy for camphene have been measured to be (8.58±0.96)×10⁻⁸ K m and (4.43±0.49)×10⁻³ J m⁻², respectively, by a direct method. The grain boundary energy of camphene has also been calculated to be (8.36±0.92)×10⁻³ J m⁻² from the observed grain boundary groove shapes.     

CdWO4 bolometers for double beta decay search

In the field of Double Beta Decay (DBD) searches, the possibility to have high resolution detectors in which background can be discriminated is very appealing. This very interesting possibility can be largely fulfilled in the case of a scintillating bolometer containing a Double Beta Decay emitter whose transition energy exceeds the one of the natural gamma line of ²⁰⁸Tl.We present the latest results obtained in the development of such a scintillating bolometer. For the first time, an array of five CdWO₄ (¹¹⁶Cd has a Double Beta Decay transition energy of 2805 keV) crystals is tested. The array consists of a plane of four 3 × 3 × 3 cm³ crystals and a second plane consisting of a single 3 × 3 × 6 cm³ crystal. This setup is mounted in hall C of the National Laboratory of Gran Sasso inside a lead shielding in order to reduce as far as possible the environmental background. The aim of this test is to demonstrate the technical feasibility of this technique through an array of detectors, and perform a long background measurement in the best conditions in order to prove the achievable background in the 0νDBD region.     

Mossbauer effect studies of the thermal decomposition of iron(II) oxalate in hydrogen

Mössbauer-effect and X-ray studies were carried out on the product samples of the thermogravimetric analysis (TGA) and of the isothermal decomposition of iron(II) oxalate in flowing H₂. Two types of sample configurations were employed for isothermal studies between 280 to 420°C for various periods of heating. Low temperature Mossbauer measurements at liquid nitrogen temperature were carried out to examine the superparamagnetic (SPM) contributions. From the spectra of samples decomposed at 340°C, in vertical experiments, the percentage SPM and percentage ferromagnetic (FM) area of Fe₃O₄ were estimated and an average size (˜167Å) for Fe₃O₄ was derived. Mossbauer measurements (at high temperatures) were carried out on Fe₃C formed in horizontal experiments, for two samples decomposed at ˜320°C for 1 hr and 2 hr. An estimate of SPM and FM Fe₃C was obtained by calculating KV, the anisotropy energy for the Fe₃C in these two samples and values of 5.07 × 10⁻¹⁶ and 7.02 × 10⁻¹⁶ erg/sec, respectively, were obtained.     

Three-dimensional measurement of ice crystals in frozen dilute solution

A Micro-Slicer Image Processing System (MSIPS) has been applied to observe the ice crystal structures formed in frozen dilute solutions. Several characteristic parameters were also proposed to investigate the three-dimensional (3-D) morphology and distribution of ice crystals, based on their reconstructed images obtained by multi-slicing a frozen sample with the thickness of 5 μm. The values of characteristic parameters were determined for the sample images with the dimension of 530×700×1000 μm. The 3-D morphology of ice crystals was found to be a bundle of continuous or dendrite columns at any freezing condition. The equivalent diameter of ice crystals were in the range of 73–169 μm, and decreased exponentially with increasing freezing rate at the copper cooling plate temperature of −20 to −80 °C. At the T_cp −40 °C, the volumes of ice crystals were in the range of 4.6×10⁴ μm³ to 3.3×10⁷ μm³, and 36 ice columns were counted in the 3-D image.     

Influence of repeller potential on ion-molecule reactions in methane and carbon tetrafluoride mixtures

Investigations of ion-molecule reactions were performed for methane-carbon tetrafluoride mixtures of different compositions. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment) and total mixture pressure was fixed at 13.3 Pa. Measurements were made using a quadrupole mass spectrometer with a high-pressure ion source. Primary ions CH₄⁺, F⁺, CF⁺ and CF₃⁺ were produced by electrons with energy of 300 eV. Secondary ions CH₅⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, C₂H₇⁺ and CF₃⁺ were observed as the result of ion-molecule reactions.The influence of repeller potential on ion-molecule reactions efficiency was examined.     

Thermoluminescence response of CaS:Bi nanophosphor exposed to 200 MeV Ag ion beam

A study of the thermoluminescence (TL) parameters has been performed on swift heavy ion exposed Bi³⁺ doped CaS nanophosphors prepared by the chemical co-precipitation method. All the samples have been exposed to 200 MeV Ag⁺¹⁵ ions in a fluence range of 1 × 10¹²–1 × 10¹³ ions/cm². The prominent TL glow peak at 403 K (observed for the γ-irradiated sample) appeared at the same position in the 200 MeV Ag⁺¹⁵ ion beam irradiated samples, while the other peak at 466 K disappeared and the broad peak normally measured at 534 K split into two peaks at 535 K and 582 K for the Ag⁺¹⁵ ion beam irradiated samples. The effect of different Bi³⁺ concentration has been investigated and it was found that the maximum TL intensity was measured for the 0.08 mol% sample. The effect of different heating rates on the TL response has also been determined. The trapping parameters (i.e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen’s formulae. The low fading and linear TL response in the range of 1 × 10¹²–1 × 10¹³ ions/cm² will be helpful to explore the potential use of this material for heavy ion dosimetry.     

Electrical transport in magnesium aluminate

The conductivity of MgAl₂O₄ has been measured at 1273, 1473 and 1673 K as a function of the partial pressure of oxygen ranging from 10⁵ to 10⁻¹⁴ Pa. The MgAl₂O₄ pellet, sandwiched between two platinum electrodes, was equilibrated with a flowing stream of either Ar + O₂, CO + CO₂ or Ar + H₂ + H₂O mixture of known composition. The gas mixture established a known oxygen partial pressure. All measurements were made at a frequency of 1 kHz. These measurements indicate pressure independent ionic conductivity in the range 1 to 10⁻¹⁴ Pa at 1273 K, 10⁻¹ to 10⁻¹² Pa at 1473 K and 10⁻¹ to 10⁻⁴ Pa at 1673 K. The activation energy for ionic conduction is 1·48 eV, close to that for self-diffusion of Mg²⁺ ion in MgAl₂O₄ calculated from the theoretical relation of Glyde. Using the model, the energy for cation vacancy formation and activation energy for migration are estimated.     

Simultaneous synthesis of high crystalline manganese oxides with layered and tunnel structures

High crystalline manganese oxides with birnessite-type (H-BirMO) and large 2 × 4 tunnel-type (Na-2 × 4) were synthesized simultaneously using a low crystalline Na-form birnessite (NaBir) as a precursor in a 2 M NaOH solution at low temperature (150 °C) and autogenous pressure. The weight ratio of the obtained Na-2 × 4 to H-BirMO was about 50. Elemental analyses indicated that Na-2 × 4 had a formula in one unit cell of Na₈Mn₂₇O₅₃·9H₂O, and the manganese average oxidation state was 3.63. H-BirMO had a formula of Na_0.31Mn_2.04O₄·0.66H₂O and the manganese average oxidation state of 3.77. H-BirMO contained a set of basal reflections with d values that correspond to a minimum periodicity along c equal to 7.06 Å. H-BirMO belonged to a monoclinic system, and the lattice parameters were a = 5.18 Å, b = 2.85 Å, c = 7.35 Å, and β = 103.3°, respectively. Na-2 × 4 showed that the first peak appeared at a d spacing of 12.07 Å in the [0 0 2] direction, and the second peak had a similar d spacing of 7.16 Å in the [2 0 0] direction with Na-birnessite in the [1 0 0] direction. FE-SEM image of H-BirMO showed a very large plate-like morphology, while SEM photograph of Na-2 × 4 consisted of nanofibers with a thickness of about 80 nm and lengths ranging between 6 and 10 μm.     

High pressure investigations of ion – Molecule reactions in a mixture of C3H8 and Ne

The gas phase reactions of positive Ne⁺ ions produced from neon with neutral propane have been studied with the use of a quadrupole mass spectrometer with a high pressure ion source. The measurements were performed in a mixture of 1% C₃H₈ and 99% Ne in the pressure range 1.33–40.00 Pa. The fractional abundances I_i/ΣI_i (relative intensity of the ion currents) of dominant C₂H₂⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, C₃H₅⁺, C₃H₇⁺ ions and neon ions have been determined as a function of the gas mixture pressure and of the repeller electrode potential ranged from 3 V to 10 V.