YbNi2: A heavy fermion ferromagnet

Measurements of the magnetization and specific heat of YbNi₂ binary alloy are reported. The DC magnetic susceptibility displays a ferromagnetic behavior with a Curie temperature T_C=10.5 K, one of the highest found in Yb compounds. Moreover, the temperature dependence of the specific heat exhibits a lambda anomaly with a peak of 5.12 J/mol K at 9.4 K. The analysis also shows an additional magnetic contribution around 32 K stemming from the crystalline electric field of a quartet at ${\Delta }_1=72\mathrm{K}$ and a doublet at ${\Delta }_2=126\mathrm{K}$, according to the splitting of the Yb³⁺ ion in cubic symmetry. From the magnetic contribution to the specific heat, a relatively high Kondo temperature $T_K=27\mathrm{K}$ is estimated. Below the magnetic transition, the specific heat shows a huge value of the electronic coefficient ${\gamma }_{\mathit{LT}}=573\mathrm{mJ}/\mathrm{mol}\mathrm{K}$, which is a signature of a heavy fermion behavior. Therefore, this alloy is a fine example of enhanced ferromagnetism and heavy fermion behavior among Yb compounds.     

Neutron induced alpha radiography

A radiography technique which makes use of $\alpha$-particles as penetrating radiation has been developed. The images were registered in the solid-state nuclear track detector CR-39 and the conditions to obtain the best radiography image were 2.2 h of irradiation and 25 min of etching in a KOH (30%) aqueous solution at $70{}^{\circ }\mathrm{C}$. For such conditions the resolution in the image was $23\mathrm{\mu }\mathrm{m}$. Some radiographs are shown and demonstrate the potential of the technique to inspect samples with thickness in the $\mathrm{\mu }\mathrm{m}$ range.     

First tests of the active shield for a gamma ray spectrometer

The operational problems of the gamma ray spectrometer shielded passively with 12 cm of lead and actively by five $0.5\mathrm{m}\times 0.5\mathrm{m}\times 0.05\mathrm{m}$ plastic veto shields are described. The active shielding effect from environmental gamma ray, cosmic muons, and neutrons was investigated. Wide range of scintillator pulses, corresponding to the energy range of 150 keV–75 MeV, was used for anticoincidence gating. With the optimal set up, the integral background of 0.31 c/s was achieved for the energy region of 50–3000 keV. The detector mass-related background was 0.345 c/kg s. The 511 keV annihilation line was reduced by factor of 7 by the anticoincidence gate. It is shown that the plastic shields increase the neutron capture gamma line intensities due to neutron termalization.     

Indentation measurements on the eardrum with automated projection moiré profilometry

Computer modeling of middle ear mechanics is an important tool to investigate its complex behavior, but correct mechanical and elastic parameters are needed to obtain realistic simulations. A possible way to determine eardrum elasticity in situ is the use of point indentation measurements. The eardrum is, however, a small fragile membrane, so a non-contacting high-resolution technique is needed to measure the shape change caused by point indentation. We have developed a projection moiré interferometer combined with an indentation actuator and a high-resolution force sensor. The apparatus applies deformations up to 1 mm with a resolution of $1\mathrm{\mu }\mathrm{m}$, while the indentation force is measured with a resolution better than 1 mN. The moiré setup delivers height data on $512\times 512$ points through phase-shifting, with a height resolution of $15\mathrm{\mu }\mathrm{m}$. Shape recordings are made on a rabbit eardrum at different indentation distances, and indentation force is recorded simultaneously.     

Principal and secondary luminescence lifetime components in annealed natural quartz

Time-resolved luminescence spectra from quartz can be separated into components with distinct principal and secondary lifetimes depending on certain combinations of annealing and measurement temperature. The influence of annealing on properties of the lifetimes related to irradiation dose and temperature of measurement has been investigated in sedimentary quartz annealed at various temperatures up to $900{}^{\circ }\mathrm{C}$. Time-resolved luminescence for use in the analysis was pulse stimulated from samples at 470 nm between 20 and $200{}^{\circ }\mathrm{C}$. Luminescence lifetimes decrease with measurement temperature due to increasing thermal effect on the associated luminescence with an activation energy of thermal quenching equal to $0.68\pm 0.01\mathrm{eV}$ for the secondary lifetime but only qualitatively so for the principal lifetime component. Concerning the influence of annealing temperature, luminescence lifetimes measured at $20{}^{\circ }\mathrm{C}$ are constant at about $33\mathrm{\mu }\mathrm{s}$ for annealing temperatures up to $600{}^{\circ }\mathrm{C}$ but decrease to about $29\mathrm{\mu }\mathrm{s}$ when the annealing temperature is increased to $900{}^{\circ }\mathrm{C}$. In addition, it was found that lifetime components in samples annealed at $800{}^{\circ }\mathrm{C}$ are independent of radiation dose in the range 85–1340 Gy investigated. The dependence of lifetimes on both the annealing temperature and magnitude of radiation dose is described as being due to the increasing importance of a particular recombination centre in the luminescence emission process as a result of dynamic hole transfer between non-radiative and radiative luminescence centres.     

Analysis of the characteristics of the polarization splitter based on tellurite glass dual-core photonic crystal fiber

A novel kind of polarization splitter based on tellurite glass dual-core photonic crystal fiber is proposed. The characteristics of the polarization splitter have been studied by the finite element method. By adjusting the ellipticity of the dual-core PCF, a very high value of birefringence can be reached. The high birefringence can increase the D-value of coupling length in the two orthogonal polarization directions, then the polarization-independent splitter can be achieved. Comparing with the SF57 glass dual-core PCF, the tellurite glass dual-core PCF has higher extinction ratio, the extinction ratio can reach ?31 dB at the wavelength $\lambda =1.55\mathrm{\mu }\mathrm{m}$. The 0.36-mm-long splitter is proposed to achieve extinction ratio better than ?10 dB and a bandwidth of 20 nm.     

Pressure behaviour of birefringence in [(CH3)2CHNH3)]4Cd3Cl10 crystal

The studies of birefringence of [(CH₃)₂CHNH₃)]₄Cd₃Cl₁₀ single crystal were carried out in the temperature interval 240–420 K and in the hydrostatic pressure range up to 570 MPa. The shift of temperature of phase transition at T₁ to higher temperature is observed with increase of pressure with the pressure coefficient ${\mathit{dT}}_1/\mathit{dp}=0.233\mathrm{K}/\mathrm{MPa}$. The shift of phase transition at T₂ to higher temperatures with the pressure coefficient ${\mathit{dT}}_2/\mathit{dp}=0.063\mathrm{K}/\mathrm{MPa}$ is observed up to about 250 MPa. At temperature T_PCP=310 K and pressure p_PCP=310 MPa the character of continuous phase transition changes to there first order and it corresponds to the tricritical point existence. Based on the studies of the temperature and pressure dependences of birefringence of [(CH₃)₂CHNH₃)]₄Cd₃Cl₁₀ crystal, its (p,T) phase diagram was constructed and its main features were discussed.     

Examining the fragmentation of 158 A GeV lead ions on copper target: Charge-changing cross sections

A stack of plastic CR-39 Track Detectors were exposed to 158 A GeV ²⁰⁷Pb ions at the CERN-SPS beam facility. The exposure of stack was performed at normal incidence with a fluence of about $1500\mathrm{ions}/{\mathrm{cm}}^2$. The total number of lead ions in each spill was about $7.8\times {10}^4$ with eight spills on each stack. For the stack with the Cu target, the lengths of etched cones on one face of the CR-39 detectors (before and after the target) were measured. Using these measurements and charge identification methodology in CR-39 track detectors, total and partial charge changing cross sections of 158 A GeV ${\mathrm{Pb}}^{82+}$ ions on Cu and CR-39 targets are determined in the charge region $63⩽Z⩽82$. The possibilities of presence and absence of odd–even effect in measured partial charge changing cross sections of 158 A GeV Pb ions for Cu and CR-39 targets are described. The charge resolution $({\sigma }_Z)$ achieved in the present experiment is $\sim 0.18\mathrm{e}$–0.21e. The analysis of discrepancies between our experimental results and other published results for the identical reaction is also presented.