Superconducting transition temperature of ion bombarded niobium carbide surface layers

The influence of Ge and C ion irradiation on the critical temperature of NbC layers obtained by the diffusion of C onto Nb-Ge-Cu substrate was studied. As a result of the irradiation with Ge ions of 150 keV and fluxes of 2.10¹⁵ and 2.10¹⁶ ion cm^–2, a slight decrease of the critical temperature, of 0.3 K and 0.6 K respectively, was observed. In both cases the critical temperature reached the pre-irradiation values after a thermal treatment for 24 h at 600° C. The irradiation with C ions of 170–180 keV and fluxes up to 2.10¹⁶ ions cm^–2 led to an increase by 30% of the critical temperature at low energies and to its degradation after the thermal treatment.     

Ultra-sensitive bolometers for atomic hydrogen detection

Two different types of bolometers have been developed to be used for spin-polarized atomic hydrogen detection. One of them uses a thin Cu shell as the absorber and a doped Ge chip as the thermometer element. The other uses a silver film as the absorber and a superconductor-insulator-normal metal junction to measure the temperature rise of the electrons in the absorber. These bolometers have a calculated noise equivalent power of 10^–15 WHz^–1/2 and 10^–17 WHz^–1/2, respectively, and can detect down to 6 × 10³ and 800 particles, respectively, at an operating temperature of 100 mK. If these detectors perform as predicted, the minimum number of detectable hydrogen atoms will be improved by several orders of magnitude.     

Nuclear recoil measurements in Superheated Superconducting Granule detectors

The response of Superheated Superconducting Granule (SSG) devices to nuclear recoils has been explored by irradiating SSG detectors with a 70MeV neutron beam. In the past we have tested Al SSG and more recently, measurements have been performed with Sn and Zn detectors. The aim of the experiments was to test the sensitivity of SSG detectors to recoil energies down to a few keV. In this paper, the preliminary results of the neutron irradiation of a SSG detector made of Sn granules 15–20µm in diameter will be discussed. For the first time, recoil energy thresholds of 1keV have been measured.     

Effect of temperature on fatigue crack growth in unplasticized polyvinyl chloride

The effect of temperature on the fatigue crack growth in a 150 mm class 12 unplasticized polyvinyl chloride (uPVC) pipe-grade material overa temperature range –30–60°C was studied. The Arrhenius relationship between fatigue crack growth rate, da/dN, and absolute temperature, T, was found to describe the experimental data very well independent of the applied stress intensity factor range, K. In the temperature range –30–10°C the activation energy was 8.8 kJ mol^–1 and between 26 and 60°C this was 30 kJ mol^–1. The two activation energies were found to be associated with two distinctly different crack growth mechanisms. In the low-temperature range there was a predominant shear mechanism, but in the high-temperature range multiple crazing was the major fatigue mechanism. Finally, a stress intensity factor—biased Arrhenius equation for fatigue crack growth was suggested and found to predict rather accurately the data of uPVC, as well as those of other polymeric materials at different temperatures.     

Low temperature hopping conduction in neutron transmutation doped isotopically enriched70Ge:Ga single crystals

The temperature dependence of variable range hopping resistivity in neutron transmutation doped (NTD) isotopically enriched⁷⁰Ge:Ga samples is reported. Five samples with compensation ratios K less than 0.001 and Ga concentrations between 3×10¹⁶ and 1.77×10¹⁷ cm^–3 were studied. All samples investigated show the ln T^–1/2 dependence in the temperature range below 1.5K. As thermistor materials NTD⁷⁰Ge:Ga samples are found to have more than factor of two higher sensitivity than commonly used natural NTD Ge in the temperature range between 0.2K and 1K. Our results are compared with theoretical predictions for variable range hopping conduction.     

Effect of ion implantation on the strength of sapphire at 300–600°C

Ion implantation with ¹¹B⁺ or ²⁸Si⁺ at 1000°C doubled the ring-on-ring flexure strength of c-plane sapphire disks tested at 300°C but had little effect on strength at 500 or 600°C. Disks were implanted on the tensile surface with 2 × 10¹⁷ B/cm² (half at 40 keV and half at 160 keV) or 1 × 10¹⁷ Si/cm² (80 keV). Sapphire implanted with 1 × 10¹⁸ B/cm² had only half as much flexure strength at 300° or 500°C as sapphire implanted with 2 × 10¹⁷ B/cm². Implantation with B, Si, N, Fe or Cr had no effect on the c-axis compressive strength of sapphire at 600°C. Boron ion implantation (2 × 10¹⁷ B/cm², half at 40 keV and half at 160 keV) induced a compressive surface force per unit length of 1.9 × 10² N/m at 20° and 1.4 × 10² N/m at 600°C. The infrared emittance at 550–800° of B-implanted sapphire at a wavelength of 5 m increased by 10–15% over that of unimplanted sapphire. Infrared transmittance of sapphire implanted with B, Si or N at either 1000°C or 25°C is within 1–3% of that of unimplanted material at 3.3 m. Implantation with Fe or Cr at 25°C decreases the transmittance by 4–8% at 3.3 m, but implantation at 1000°C decreased transmittance by only 2–4% compared to unimplanted material.     

Muon and neutron-induced background in gamma-ray spectrometry

A low-background γ-ray spectrometer for environmental surveillance, emergency response, and environmental health research has been constructed. It consists of a 132% efficient HPGe detector, graded lead shielding, and muon-rejection shielding, as well as external steel and building shielding. Detailed operation of the γ spectrometer and all of its components is described. Cosmic-ray muon and cosmic-neutron-induced background was accurately measured, and is discussed. We have achieved an overall background reduction by a factor of 9436 relative to the ambient level. Our integrated background rate in the γ energy range of 50-2700 keV was measured as 2.3 counts per min, corresponding to 15 counts ks⁻¹ kg⁻¹ Ge. Future directions in low-background γ spectroscopy at our facility are described.     

Spin Properties of Electrons in Low-Dimensional SiGe Structures

Using ESR, we investigate g-factor and spin coherence time of electrons confined in 2D Si_1–xGe_x {channels} (x < 0.1) by barriers with x > 0.2 and in SiGe quantum dots grown on prepatterned Si substrates. The quantum wells exhibit 2D-anisotropy of both g and which can be explained in terms of the Bychkov–Rashba field. The latter increases with increasing Ge content in the well indicating that the increasing spin-orbit coupling is more important than interface properties. The narrow ESR permits selective spin manipulation already for x > 0.02. Large, regular arrays of Ge quantum dots (about 10⁹) were grown on prepatterned substrates. Strain in the Si capping layer lowers the conduction band relative to that of Ge causing confinement. The g-shift observed implies the possibility of g-tuning by confinement. The line width shows substantial inhomogeneous broadening whereas the longitudinal spin lifetime is hardly changed with respect to 2D structures.     

Aerobic composting of tobacco industry solid waste—simulation of the process

Solid waste accumulated during the processing of tobacco for cigarette manufacture mostly contains tobacco particles and flavoring agents. Its main characteristics are a high content of nicotine (2,000 mg per kg of total solids), which is a toxic compound, and high value of total organic carbon of the aqueous extract (12,620.0 mg l^–1). Because of this fact tobacco waste cannot be disposed of with urban waste.The aim of this work was to stabilize tobacco solid waste by aerobic composting. The experiments were carried out in closed thermally insulated column reactors (1.0 l and 25 l) under adiabatic conditions and at an airflow rate of 0.9 l min^–1 kg^–1 of volatile solids for 16 days. During the process, temperature changes in the reactor, CO₂ production and the numbers of mesophilic and thermophilic organisms in the mixed microbial culture were closely monitored. Nicotine concentration in the samples was analyzed at the start and at the end of process. It was estimated that at the end of composting the volume and mass of total solids in the tobacco waste were reduced by about 50% and those of nicotine by 80%. A simple empirical model was used to simulate the biodegradation rate of the organic fraction of the solid waste. It was found that the selected model describes aerobic composting fairly well, although only two kinetic parameters (k₀ and n) were estimated.List of symbols c_pS specific heat capacity of the substrate, kJ kg^–1 K^–1 - c_pz specific heat capacity of air, kJ kg^–1 K^–1 - F_Ku and F_Ki molar airflow at the reactor inlet and outlet, mol h^–1 - H_r reaction enthalpy, kJ kg^–1 of dry substrate - k specific rate, Eqs. (5) and (9), h^–1 - k_o constant in Eq. (9), day^–1 - m_o initial mass of the substrate, kg - m_S mass of dry substrate, kg - n order of the reaction in Eq. (5) - n_K molar amount of oxygen, mol - Q_v airflow volume, m³ h^–1 - r_K oxygen depletion rate, mol kg^–1 h^–1 - r_S degradation rate, kg kg^–1 h^–1 - _z air density, kg m^–3 - SD mean square deviation - t time, h - T temperature in reactor, °C - T_o temperature of substrate at the beginning of reaction, °C - T_K temperature of compost at the end of reaction, °C - T_u temperature of air at the reactor inlet - space time, day - w_S mass fraction of compost, m_sm_o^–1, kg kg^–1     

Low cost porous mullite-corundum ceramics by gelcasting

A gelcasting process has been successfully employed to fabricate porous mullite-corundum ceramic composites from natural clay and corundum powders. The specimens based on the mullite composition are found with an open porosity of 45–47.9%, mean pore size of 1.28–2.55 m, and nitrogen permeability of 965–5038 m³· m^–2· bar^–1· hr^–1by reactively sintering the gelled mixture of kaolinite and -alumina at 1100–1500°C. The open porosity (_o), mean pore size (d _p), pore size distribution and gas permeability can be controlled by adjusting raw material ratios and sintering temperatures. The gas permeability of the specimens is found to be more dependent on the pore size distribution as well as d _pthan on _o. In addition, the gas transportation mechanism in porous mullite-corundum ceramic composites is dominated by viscous flow.     

Scintillating Bolometers for Rare Events Searches: The LUCIFER Experiment

The main goal of LUCIFER is the study of the neutrino-less double beta decay, a rare process that, if detected, could demonstrate the Majorana nature of neutrino and set the absolute mass of this particle. Dealing with rare decays, one of the most critical issues of the experiment is the background reduction. This requirement will be satisfied by LUCIFER thanks to the use of Zn \(^{82}\) Se scintillating bolometers: the simultaneous read-out of heat and light emitted by the interactions in the detector will allow to reject most of the spurious events, providing a background of 10 \(^{-3}\)  counts/keV/kg/year at the transition energy of \(^{82}\) Se (2,997 keV). The detector will be made by tens of \(\sim \) 0.5 kg ZnSe crystals and Ge light detectors operated as bolometers at 10 mK. We present the results obtained with a single detector module in terms of energy resolution, radio-purity and background rejection capability. In addition, we discuss the feasibility of dark matter searches in the framework of the LUCIFER experiment.     

Fabrication and properties of an anisotropic PZT/polymer 0–3 composite

Anisotropic 0–3 PZT platelet/polymer composites were prepared by a route involving the tape casting and sintering of PZT sheets and the subsequent alignment of platelets in a polymer matrix by either calendering or tape casting; both techniques induced a strong alignment of the platelets. At 60 vol 1/2 loading, measured d ₃₃- and d _h-values of ~ 30 pC N^–1 and ~ 100 pC N^–1, respectively, were obtained; the calculated g _h-value was 83 mV mN^–1. A strong relaxation effect observed is considered most likely to be dependent on the characteristics of the polymer phase.     

The effect of particles on the critical strain associated with the Portevin-LeChatelier effect in aluminium alloys

The effect of particles on the critical strain, _c, associated with the Portevin-LeChatelier (PL) effect of aluminium alloys is studied using Al-Mg-Ni and Al-Si alloys. Al-Mg-Ni and Al-Si alloy matrixes are composed of Al₃Ni and Si particles, respectively. Tensile tests were performed in the temperature range 223–273 K in which the critical strain decreases with increasing temperature, and strain rates between 10^–5 and 10^–2 s^–1 were chosen. According to the apparent activation energies, Q, Mg and Si solute atoms are responsible for the flow instability in Al-Mg-Ni and Al-Si alloys, respectively. The experimental results also show that the critical strain decreases with decreasing particle spacing, d _p. Since the particle spacing is small compared to the corresponding grain size, the decrease in critical strain should be ascribed to the effect of particles. Considering that the dislocation density is increased by the particles, a modified model showing the critical strain, _c, as a function of particle spacing, d _p, is proposed as T ^–1 exp (–Q/kT), in which , T and k are the strain rate, temperature and Boltzmann constant, respectively. Linear fit of the plots of In _c versus In d _p and In _c versus In d _p indicates that this equation is appropriate to rationalize the particle effect on the critical strain.     

Surface free energy of nickel and stainless steel at temperatures above the melting point

The surface tension (liquid-state surface free energy) of pure nickel and type 304 stainless steel was measured in a narrow temperature range above the melting point by the sessile drop method. The temperature coefficients of surface free energy in the liquid state were found to be –1.76 erg cm^–2 C^–1 for nickel and –2.48 erg cm^–2 C^–1 for stainless steel. These values are shown to be a factor of 2 larger than those previously determined for the solid surface free energies of nickel and stainless steel, but have the same sign. The latent heats of fusion of nickel and 304 stainless steel were determined by comparison of variations of solid and liquid-state surface energies with temperature and found to be 292 and 284 erg cm^–2 respectively. Measurement of the contact angle for a nickel sessile drop on thoria and a stainless steel sessile drop on alumina showed a decrease in the angle with an increase in temperature.     

Spin Properties of Electrons in Low-Dimensional SiGe Structures

Using ESR, we investigate g-factor and spin coherence time of electrons confined in 2D Si_1–xGe_x {channels} (x < 0.1) by barriers with x > 0.2 and in SiGe quantum dots grown on prepatterned Si substrates. The quantum wells exhibit 2D-anisotropy of both g and which can be explained in terms of the Bychkov–Rashba field. The latter increases with increasing Ge content in the well indicating that the increasing spin-orbit coupling is more important than interface properties. The narrow ESR permits selective spin manipulation already for x > 0.02. Large, regular arrays of Ge quantum dots (about 10⁹) were grown on prepatterned substrates. Strain in the Si capping layer lowers the conduction band relative to that of Ge causing confinement. The g-shift observed implies the possibility of g-tuning by confinement. The line width shows substantial inhomogeneous broadening whereas the longitudinal spin lifetime is hardly changed with respect to 2D structures.     

High Z bolometers for analysis of internal β and α activities

CdWO₄ bolometers were realized with the final purpose to study Double Beta Decay of¹¹⁶Cd. The test device we developed performs as a very efficient detector, with a preliminary resolution of aboout 5 keV FWHM. The detector background spectra are dominated at low energies by decay of¹¹³Cd: the calorimetric measurement of this process allows to detrmine the end point (318.8±1.4±5 keV) and with unprecedented precision the life time ((9,3±0.5±1)×10¹⁵ y). Following the same approach, we have analysed the internal contamination in²¹⁰Pb of three different types of lead used for shielding in low background experiments. Various lead bolometers were developed and operated, using common modern lead, special low activity modern lead and 2000 years old Roman lead. The presence of²¹⁰Pb was clearly observed through the decay of its daughter²¹⁰Po in the modern samples, while only a limit was set for the much purer Roman lead. The purifying effect of crystallization was clearly demontrated.as far as the part about CdWO₄ is concerned     

Energy sensitive detection of heavy ions with transition edge calorimeters

Status and results of a research project are reported, which aims at developing calorimetric low temperature detectors for heavy ions. The special conditions for the detection of energetic heavy ions are discussed. The response of an aluminium transition edge calorimeter, operated at about1.5K, to the impact of heavy ions was investigated. The observed energy resolutions E/E=3.9×10^–3for5.9MeV/u ²⁰⁸ Pb-ions, E/E=1.6×10^–3for4.8MeV/u ⁵⁸ Ni-ions and E/E=4.3×10^–3for100MeV/u ²⁰ Ne-ions are most probably not yet limited by the intrinsic detector resolution. The present results already represent an improvement over conventional solid state detectors and ionization chambers.     

Effects of Quasiparticle Recombination and Photoelectron Escape in Al-Superconducting Tunnel Junction Detectors

A slight deviation from linearity has been detected for single aluminum superconducting tunnel junction detectors (100×100×0.52=0.35 m³) in the energy range between E=1.74 keV and E=6.49 keV. The nonlinearity can be explained by the escape of recombination phonons into the substrate. Varying the size of the junction shows that the recombination of the quasiparticles takes place after their diffusive propagation across the junction, hot spot effects are not observed. Energy resolution obtained with aluminum tunnel junction detectors so far is not affected by recombination effects. Pulse shape analysis allows to deconvolve the double-peak structure of the pulse height spectra and to identify background events that are caused by the range of photo- and Auger-electrons. The range of photoelectrons (E_kin=4.34 keV) is determined to be 0.2 m in aluminum. In the pulse height spectrum, the escape of photoelectrons produces a flat background.     

Fatigue crack growth of polycarbonate under high pressures

In order to investigate the effect of hydrostatic pressure on the fatigue crack growth behaviour of solid polymers, an apparatus was designed for maximum pressure of 3000 kgf cm^–2. The crack growth rates as a function of stress intensity factor range, K, were measured using compact tension specimens of polycarbonate under pressures of 1–2000 kgf cm^–2. It was shown that (1) the fatigue crack growth rates at pressures higher than 500 kg cm^–2 were nearly insensitive to hydrostatic pressure, (2) the slope on a log (dc/dN) versus log (K) diagram was higher at the high pressures than at an atmospheric pressure, and (3) shear lips and the tear lines appeared on the fracture surfaces at atmospheric pressure, while they were not observed at pressures higher than 500 kgf cm^–2.     

Analytical technique for the determination of solidification rates during the inward freezing of cylinders

An analytical/experimental approach which permits the determination of solidification rates during the inward solidification of cylinders is proposed. The technique is based on a previous analytical solution that treats the generalized problem of solidification of slabs. This solution is modified by a geometric correlation to compensate for the cylindrical geometry. A number of experiments have been carried out with a special experimental set-up, designed to simulate the inward solidification of cylinders in a water-cooled mould. A series of comparisons of experimental results, numerical predictions and calculations furnished by the proposed technique were made, showing good agreement for any case examined.Nomenclature a _s Thermal diffusivity of solid metal = k _s/c _s d _s (m² sec^–1) - A _i Internal surface area of the mould (m²) - b _s Heat diffusivity of solid metal = (k _s c _s d _s ^1/2(J m^–2 sec^–1/2 K^–1) - c _s Specific heat of solid metal (J kg^–1 K^–1) - d _s Density of solid metal (kg m^–3) - h Newtonian heat transfer coefficien (W m^–2 K^–1) - H Latent heat of fusion (J kg^–1) - k _s Thermal conductivity of solid metal (W m^–1 K^–1) - q Heat flux (W m^–2) - r Radial position (m) - r _o Radius of cylinder (m) - r _f Radius of solid/liquid interface (m) - S Thickness of solidified metal (m) - S _o Thickness of metal side adjunct (m) - t Solidification time (sec) - T Temperature (K) - T _i Surface temperature (K) - T _f Freezing temperature of metal (K) - T _o Temperature of the coolant (K) - T _s Temperature at any point in the solidified metal (K) - V ₁ Volume of remaining liquid metal during the solidification (m³) - V _s Volume of solidified metal (m³) - V _T Total volume of metal in the mould (m³) - x Distance from metal/mould interface (m) - Dimensionless solidification constant.