A neutron diffraction investigation of some β′-sialons

Neutron diffraction measurements have been made on -sialons having chemical compositions Si₆-zAlzOzN₈-z, where Z=2.0, 2.9 and 4.0. The powder diffraction patterns have been recorded for sample temperatures of 300 K and 4.2 K, and the profile refinement method has been used in the data analysis. The unit-cell dimensions and the atomic co-ordinates were found to vary in a regular way with composition. The values of scattering amplitude per atomic site obtained using the refinement method provide evidence of a preferential replacement of nitrogen by oxygen on specific crystallographic sites, and an indication of a small vacancy concentration on the metal-atom sites.     

Practical aspects of neutron activation in VVÉR fields

The paper discusses neutron activation in basic research aspects of VVÉR fields.A library of typical VVÉR spectra is proposed, and characteristic integral cross sections are given for recommended activation reactions, with a discussion of neutron-activation detectors standardized in Russia for this form of measurement.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 67–71, January, 2005.     

BUMS—Bonner sphere Unfolding Made Simple: an HTML based multisphere neutron spectrometer unfolding package

A new multisphere neutron spectrometer unfolding package, Bonner sphere Unfolding Made Simple (BUMS) has been developed that uses an HTML interface to simplify data input and code execution for the novice and the advanced user. This new unfolding package combines the unfolding algorithms contained in other popular unfolding codes under one easy to use interface. The interface makes use of web browsing software to provide a graphical user interface to the unfolding algorithms.BUMS integrates the SPUNIT, BON, MAXIET, and SAND-II unfolding algorithms into a single package. This package also includes a library of 14 response matrices, 58 starting spectra, and 24 dose and detector responses. BUMS has several improvements beyond the addition of unfolding algorithms. It has the ability to search for the most appropriate starting spectra. Also, plots of the unfolded neutron spectra are automatically generated.The BUMS package runs via a web server and may be accessed by any computer with access to the Internet at http://nukeisit.gatech.edu/bums.     

Polarized infrared and neutron scattering studies of α-Bi2O3

Studies on the lattice dynamics of -Bi₂O₃ have been performed including IR polarized reflectance spectra on single crystal, inelastic neutron scattering and specific heat measurements. Dispersion parameters and polarizations of IR-active phonons are presented and compared with neutron and specific heat data.     

Experimental investigation of the metrological characteristics of the scintillation spectrometer in mixed gamma–neutron fields

A small-dimension scintillation spectrometer for measurements in mixed gamma–neutron fields is described. The block scheme and general characteristics of the spectrometer are given. The measured neutron and gamma-spectra are shown.     

In situ high-temperature X-ray and neutron diffraction of Cu–Mn oxide phases

Copper–manganese oxides were analyzed by in situ high-temperature powder neutron and X-ray diffraction to investigate their crystal structure. Cu–Mn spinel was found to form a continuous solid solution with cubic symmetry between Mn₃O₄ and Cu₂MnO₄. A high-temperature phase with approximate composition Cu₅Mn₄O₉ was shown to have hexagonal symmetry. The cation distribution and lattice parameters of Cu–Mn spinel were resolved through Rietveld refinement of in situ neutron diffraction data. The results demonstrated that the Cu ion has a lower octahedral site preference than manganese ions, and quenching is not a reliable method to determine the equilibrium structure in the system.     

An X-ray and neutron reflectometry study of ‘PEG-like’ plasma polymer films

Plasma-enhanced chemical vapour-deposited films of di(ethylene glycol) dimethyl ether were analysed by a combination of X-ray photoelectron spectroscopy, atomic force microscopy, quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray and neutron reflectometry (NR). The combination of these techniques enabled a systematic study of the impact of plasma deposition conditions upon resulting film chemistry (empirical formula), mass densities, structure and water solvation, which has been correlated with the films'' efficacy against protein fouling. All films were shown to contain substantially less hydrogen than the original monomer and absorb a vast amount of water, which correlated with their mass density profiles. A proportion of the plasma polymer hydrogen atoms were shown to be exchangeable, while QCM-D measurements were inaccurate in detecting associated water in lower power films that contained loosely bound material. The higher protein resistance of the films deposited at a low load power was attributed to its greater chemical and structural similarity to that of poly(ethylene glycol) graft surfaces. These studies demonstrate the utility of using X-ray and NR analysis techniques in furthering the understanding of the chemistry of these films and their interaction with water and proteins.     

Normal penetration of an eroding projectile into an elastic–plastic target

The main objective of the present work is to describe normal penetration of a deformable projectile into an elastic–plastic target. The force imposed on the projectile by the target is generally a complex function of the strength of the target material, the projectile velocity, its diameter and shape, as well as the instantaneous penetration depth. When this force exceeds a certain critical value the projectile begins to deform. At moderate-to-high values of the impact velocity, the projectile's tip material flows plastically with large deformations causing the formation of a mushroom-like configuration. This process is accompanied by erosion of the projectile material. In the rear (“elastic”) part of the projectile the deformations remain small and the region can be approximated as a rigid body being decelerated by the projectile's yield stress. The general model allows one to predict the penetration depth, the projectile's eroded length and the crater diameter. It has been shown that in the limit of very high impact velocities the present model reduces to the well-known form of the hydrodynamic theory of shaped-charge jets. Also, a simplified asymptotic formula for the crater radius has been derived which includes the effect of the target's yield stress and compares well with experimental data for very high impact velocities.     

The influence of neutron irradiation on the thermal conductivity of aluminum in the range 5–50 K

Measurements of thermal conductivity of 6N to 3N pure aluminum in the temperature range 5–50 K subjected to fast neutron irradiation, with exposures of 10¹³ and 10¹⁶ n · cm^–2, are reported. The thermal conductivity maximum was found to shift towards higher temperatures with an increase in the fast neutron irradiation exposure. At high temperatures, a departure from Wilson's theory was observed, which may be attributed to the existence of additional electron scattering mechanisms. An increase in both ideal and residual thermal resistivity components with an increase in the radiation exposure was noted.Nomenclature I ₅ (/t) Debye integral of the fifth order - –m slope of the straight line that crosses maximum thermal conductivity values - n exponent in ideal thermal resistivity component - T _m temperature corresponding to maximum thermal conductivity - W _e total electronic thermal resistivity - W _i ideal thermal resistivity - W ₀ residual thermal resistivity - ideal thermal resistivity coefficient in Eq. (4) - ideal thermal resistivity coefficient in Eq. (1) - constant related to the ideal part of thermal resistivity in Eq. (2) - () ideal thermal resistivity coefficient depending on irradiation exposure - () residual thermal resistivity coefficient depending on irradiation exposure - thermal conductivity - _m maximum thermal conductivity - Debye characteristic temperature - irradiation exposure     

Measurements of (n,γ) neutron capture cross-sections with liquid scintillator detectors

A method for measuring (n,γ) neutron capture cross-sections using liquid scintillator detectors has been investigated. If the response function of the detector is known, and the efficiency as a function of energy is low and approximately constant, then gamma cascades can be counted via a method that is independent of the cascade path provided the detector response is manipulated to allow detection efficiency to be proportional to emitted gamma-ray energy.In this paper, we demonstrate the measurement of efficiency and response functions for a C₆D₆ liquid scintillator using gamma-ray sources and (p,γ) reactions on light nuclei. Methods to reproduce the detector response and efficiency data successfully using simulations are presented and discussed. An entire response matrix for the detector has been constructed using a new interpolation technique, allowing weighting functions that force the detector efficiency to be proportional to gamma-ray energy to be calculated. An analysis of the sources of error involved in making (n,γ) cross-section measurements with this method has been undertaken using Monte-Carlo simulation techniques.     

Study of d–t neutron energy spectra at JET using natural diamond detectors

Four natural diamond detectors (NDDs) have been used for deuterium–tritium neutron spectrometry and flux monitoring during the 1997 tritium experiments (DTE1) carried out in the Joint European Torus (JET).Neutron energy spectra have been measured with three NDDs for discharge scenarios that included (a) hot ion H-mode studies using combined neutral-beam (NB) and ion cyclotron resonance frequency (ICRF) heating, (b) optimized shear experiments using combined NB and ICRF heating, (c) alpha-particles heating experiments with NB heating only and (d) ICRF heating studies without NB heating. Within the statistical accuracy of the data, the spectra can be adequately represented by Gaussian distributions, whose fwhm values provide effective ion temperatures that characterize the energy distributions of the ions taking part in fusion reactions.     

Application of Design of Experiments for AlloyDevelopment of an Aluminum Copper Casting Alloy

Design of experiments (DoE) based on a linear regression model was used to develop an Aluminum Copper-based casting alloy. The main objectives of the development were the achievement of (1) a high strength at elevated temperatures with (2) a low hot tearing tendency. Within the DoE, 17 different chemical compositions of the newly developed alloy AlCuMnCo(Ni) were cast, tested regarding hot tearing tendency and characterized in tensile tests up to 300 °C. Test results showed that the AlCuMnCo(Ni)-alloys from the DoE have high mechanical properties from ambient temperature up to 300 °C and thus feature a high thermal stability. It was found that the alloying elements Cu and Co increase the yield strength whereas Mn and Ni tend to increase the attainable elongation. Furthermore, some of the alloys showed no or a very low tendency to hot tearing a remarkable feature for Al-Cu alloys which are otherwise highly susceptible to hot tearing. The regression model that was developed from the test results fulfils a set of quality criteria and is therefore expected to provide reliable predictions. The predictive ability of the model was validated by casting and testing a sweet spot alloy. Results show that the model is sufficient for predicting the mechanical properties from ambient temperature to 250 °C. Furthermore, the sweet spot alloy surpasses the reference alloy AlCuNiCoSbZr (RR30) in its mechanical properties up to 250 °C. It was shown that by applying design of experiments, time and effort for an alloy development can effectively be reduced and simultaneously a high degree of information density about the alloying system considered is generated.     

Use of radioisotopes (1–92) made at a steady state neutron facility

The use of reactor-produced radioisotopes is reviewed, with emphasis on those applications which require high neutron fluxes. Considerable opportunities are noted for new or improved utilization if neutron fluxes in the 10²⁰/m² s range can be achieved. New uses are seen in medical applications, condensed matter research and in a variety of industrial applications.     

Isothermal Crystallization Kinetics of an Amorphous CuTi Alloy

Isothermal crystallization kinetics ofCu_(40)Ti_(60)amorphous alloy has been studied usingdifferential scanning calorimetry(DSC).Bothas-quenched and pre-annealed ribbons were inves-tigated.For crystallization of as-quenched amor-phous ribbon in Ar,it was found that the kineticsfollows Johnson-Mehl-Avrami equation withmean Avrami exponent n=2.58,which indicatesthat crystallization of amorphous Cu_(40)Ti_(60)is athree-dimensional diffusion controlled growth pro-cess with constant nucleation rate,i.e.,primarycrystallization process.The primary phase is thetetragonal CuTi_2.The as-quenched amorphousribbons were also crystallized in air,the results re-veal that oxidation has no significant influence oncrystallization kinetics of amorphous Cu_(40)Ti_(60).The results of crystallization of pre-annealed rib-bons show a decreasing tendency of Avrami expo-nent with increasing pre-anneal time.The localactivation energy and local Avrami exponent dur-ing crystallization process of as-quenched amor-phous alloy were also examined.     

Monitoring of an ATP-binding aptamer and its conformational changes using an α-hemolysin nanopore

An aptamer is a specific oligonucleotide sequence that spontaneously forms a secondary structure capable of selectively binding an analyte. An aptamer's conformation is the key to specific binding of a target molecule, even in the case of very closely related targets. Nanopores are a sensitive tool for the single-molecule analysis of DNA, peptides, and proteins transporting through the pore. Herein, a single α-hemolysin natural nanopore is utilized to sense the conformational changes of an adenosine 5'-triphosphate (ATP)-binding aptamer (ABA). The known DNA sequence of the ABA is used as a model to develop real-time monitoring of molecular conformational changes that occur by binding targets. The native, folded ABA structure has a nanopore unfolding time of 4.17 ms, compared with 0.29 ms for the ABA:ATP complex. A complementary 14-mer strand, which binds the ABA sequence in the key nucleic acids responsible for folding, forms linear duplex DNA, resulting in a nanopore transit time of 0.50 ms and a higher capture probability than that of the folded ABA oligomer. Competition assays between the ABA:ATP and ABA:reporter complexes are carried out, and the results suggest that the ABA:ATP complex is formed preferentially. The nanopore allows for the detection of an ABA in its folded, ATP-bound, and linear conformations.     

A method for measuring the neutron flux from an AmBe source using a Nal(Tl) scintillator

We present a simple method for measuring the neutron flux from an ²⁴¹Am-Be radioactive source. The yield determination is based on counting (n,p) + (n,d) and (n,α) events in a NaI(Tl) scintillator. This technique offers the advantages of two independent measurement of the flux rather than one, insensitivity to the threshold setting used for counting, and low sensitivity to edge effects.     

Shape Memory Effect of an Aged Fe-Mn-Si-Co-Mo Alloy

The effect of ageing on the microstructure, mechanical properties and shape memory effect (SME) in a newly developed Fe-24Mn-5Si-8Co-4Mo shape memory alloy has been studied. It was found that Fe2Mo particles precipitate during ageing and thereby increase hardness and strength of the alloy The SME of the alloy can be remarkably improved by ageing and a maximum SME can be obtained when aged at 873 K. When the ageing temperature is over 873 K, the SME decreases with increasing ageing temperature. The reason for the improvement of SME by ageing in the Fe-Mn-Si-Co-Mo alloy is discussed