Automated sample exchange and tracking system for neutron research at cryogenic temperatures

An automated system for sample exchange and tracking in a cryogenic environment and under remote computer control was developed. Up to 24 sample "cans" per cycle can be inserted and retrieved in a programed sequence. A video camera acquires a unique identification marked on the sample can to provide a record of the sequence. All operations are coordinated via a LABVIEW program that can be operated locally or over a network. The samples are contained in vanadium cans of 6-10 mm in diameter and equipped with a hermetically sealed lid that interfaces with the sample handler. The system uses a closed-cycle refrigerator (CCR) for cooling. The sample was delivered to a precooling location that was at a temperature of approximately 25 K, after several minutes, it was moved onto a "landing pad" at approximately 10 K that locates the sample in the probe beam. After the sample was released onto the landing pad, the sample handler was retracted. Reading the sample identification and the exchange operation takes approximately 2 min. The time to cool the sample from ambient temperature to approximately 10 K was approximately 7 min including precooling time. The cooling time increases to approximately 12 min if precooling is not used. Small differences in cooling rate were observed between sample materials and for different sample can sizes. Filling the sample well and the sample can with low pressure helium is essential to provide heat transfer and to achieve useful cooling rates. A resistive heating coil can be used to offset the refrigeration so that temperatures up to approximately 350 K can be accessed and controlled using a proportional-integral-derivative control loop. The time for the landing pad to cool to approximately 10 K after it has been heated to approximately 240 K was approximately 20 min.     

中速定向凝固K10高温合金的组织和偏析的研究

本文利用最新研制的ZMLMC（区域熔化液态金属冷却）超高温度梯度定向凝固装置研究了钴基高温合金K10在中等冷却速率下定向凝固时的微观组织变化和枝晶偏析及其与凝固参数的关系。结果表明,钴基高温合金K10在中速定向凝固后,其一次枝晶间距比传统的HRS法定向凝固组织细化5倍以上,并在一定的冷却速率下获得了二次分枝被强烈抑制、一次轴呈平行排列的定向凝固超细柱晶组织,在所研究的冷却速率范围内,合金元素Cr、Mo和Ni在枝晶干与枝晶间的偏析比均随冷却速率的增大而趋于1,枝晶偏析得到抑制甚至消除。     

Temperature directly affects the rate of irradiation-induced mass loss from phosphatidylcholine multilayers

We monitored the mass thickness of egg yolk phosphatidylcholine multilayers at several temperatures during electron irradiation. The rate of irradiation-induced mass loss was reduced substantially when this specimen was cooled to liquid nitrogen temperature from room temperature. Additional cooling to liquid helium temperature caused an additional reduction of mass-loss rate. The characteristic doses D(1/e), which are the slopes of the logarithm of the differential mass thickness against dose, were approximately 7 x 10(3) e/nm2 at 290 K, 8 x 10(4) e/nm2 at 130 K, and 1.4 x 10(5) e/nm2 at less than 10 K. The fractions of the original mass thickness that remained after arbitrarily high doses were about 69% at 290 K, 72% at 130 K, and 77% at less than 10 K.     

Present status of traceability and accuracy of dimensional measurement in Japan

The establishment and maintenance of the traceability of standards in Japan is rightly seen as an important task of the National Research Laboratory of Metrology. In this article, T. Katoh, M. Sawabe, K. Sakamoto and S. Seino outline the procedures and the results of three round robin measurements of gauge blocks by interferometry and by comparators, of ring gauges and plug gauges involving local branches of the National Laboratory and manufacturers' metrology laboratories. An encouraging improvement in gauge block measurement by interferometry has been noted over the past 20 years; they are now being measured to within 0.03 μm     

冷速对液态Ti_3Al合金快速凝固过程中微观结构变化的影响

采用分子动力学方法模拟研究了不同冷速条件下液态Ti3Al合金的凝固过程。采用对相关函数法、原子团类型指数法(CTIM)对凝固过程中团簇结构的变化进行了分析。结果表明:在以1×1012K/s,1×1013K/s,1×1014K/s三种不同冷速条件下,系统都形成了以(12 0 12 0)基本原子团为主的非晶态结构,冷速对于Ti3Al合金凝固过程微观结构的影响主要是通过(12 0 12 0)基本原子团数目变化体现出来,(12 0 12 0)基本原子团在Ti3Al合金快速凝固过程团簇结构演变中起了主要作用。冷速越低,Ti3Al合金的玻璃态转化温度越低,体统形成的(12 0 12 0)基本原子团数目越多,非晶体的结构越稳定。     

On the effects of lateral gauge misalignment in shocked targets

Plate-impact experiments have been used to interrogate the influence of gauge alignment on the shock response of wire-element lateral manganin stress gauges in PMMA and aluminium targets. Embedded gauges were progressively rotated relative to the target impact face. Peak stress and lateral gauge rise-times were found be proportional (negatively and positively, respectively) to the resolved angle of the embedded gauge element. However, lateral stress gradients behind the shock were found to be relatively insensitive to gauge alignment. In addition, investigation of the effects of release arrival showed no connection to either peak stress or behaviour behind the shock.     

Automatic 300-4 K temperature cycling apparatus

The apparatus described here automatically cycles small samples between 300 and 4 K by alternately raising and lowering the sample through the neck of a commercial liquid helium storage Dewar. A bellows, which is pressurized by the helium boil-off gas, provides all of the required mechanical motion. By utilizing the cooling available from the boil-off gas, liquid helium helium consumption is limited to 0.03 l/cyc for a 12-g sample. Cycle times can be as short as 5 min.     

Ultra-rapid freezing by spraying/plunging: pre-cooling in the cold gaseous layer

A thermophysical model is established to analyse the influence of pre-cooling of a biological specimen in the cold gas layer associated with spray-freezing techniques. The basic principles governing the process of pre-cooling are provided. It is concluded that pre-cooling is one of the major limiting steps in attaining an overall ultra-rapid cooling rate. Pre-cooling has a substantial influence on the nature of the final frozen specimens. In order completely to avoid crystallization before entry into the liquid cryogen and maximize the overall cooling rate of the specimen, precautions should be taken to control the height of the gaseous layer and the size of the specimen. The probability of the specimen being frozen in the cold gaseous layer is reduced by increasing the entry speed. The effectiveness, however, becomes less marked at speeds greater than 10 m/s. In order to minimize the risk of misinterpreting the measured cooling rate, it is necessary to specify the pre-cooling conditions. The pre-cooling effect is much more evident in liquid helium than in cryogens such as propane, ethane, Freon 12, 13 and 22.     

Differential membrane-based nanocalorimeter for high-resolution measurements of low-temperature specific heat

A differential, membrane-based nanocalorimeter for general specific heat studies of very small samples, ranging from 0.5 mg to sub-μg in mass, is described. The calorimeter operates over the temperature range from above room temperature down to 0.5 K. It consists of a pair of cells, each of which is a stack of heaters and thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The device has several distinctive features: (i) The resistive thermometer, made of a Ge(1 - x)Au(x) alloy, displays a high dimensionless sensitivity ∣dlnR∕dlnT∣ ? 1 over the entire temperature range. (ii) The sample is placed in direct contact with the thermometer, which is allowed to self-heat. The thermometer can thus be operated at high dc current to increase the resolution. (iii) Data are acquired with a set of eight synchronized lock-in amplifiers measuring dc, 1st and 2nd harmonic signals of heaters and thermometer. This gives high resolution and allows continuous output adjustments without additional noise. (iv) Absolute accuracy is achieved via a variable-frequency-fixed-phase technique in which the measurement frequency is automatically adjusted during the measurements to account for the temperature variation of the sample heat capacity and the device thermal conductance. The performance of the calorimeter is illustrated by studying the heat capacity of a small Au sample and the specific heat of a 2.6?μg piece of superconducting Pb in various magnetic fields.     

Development of a low-temperature photoelectron spectroscopy instrument using an electrospray ion source and a cryogenically controlled ion trap

The ability to control ion temperatures is critical for gas phase spectroscopy and has been a challenge in chemical physics. A low-temperature photoelectron spectroscopy instrument has been developed for the investigation of complex anions in the gas phase, including multiply charged anions, solvated species, and biological molecules. The new apparatus consists of an electrospray ionization source, a three dimensional (3D) Paul trap for ion accumulation and cooling, a time-of-flight mass spectrometer, and a magnetic-bottle photoelectron analyzer. A key feature of the new instrument is the capability to cool and tune ion temperatures from 10 to 350 K in the 3D Paul trap, which is attached to the cold head of a closed cycle helium refrigerator. Ion cooling is accomplished in the Paul trap via collisions with a background gas and has been demonstrated by observation of complete elimination of vibrational hot bands in photoelectron spectra of various anions ranging from small molecules to complex species. Further evidence of ion cooling is shown by the observation of H2-physisorbed anions at low temperatures. Cold anions result in better resolved photoelectron spectra due to the elimination of vibrational hot bands and yield more accurate energetic and spectroscopic information. Temperature-dependent studies are made possible for weakly bonded molecular and solvated clusters, allowing thermodynamic information to be obtained.     

On the design of capacitive sensors using flexible electrodes for multipurpose measurements

This article evaluates the potential of capacitive measurements using flexible electrodes to access various physical quantities. These electrodes are made of a thin metallic film, typical thickness 0.2 microm, evaporated on a plastic substrate. Their large flexibility enables them to be mounted in complex geometries such as curved surfaces. In the configuration of planar condensers, using a very sensitive commercial capacitive bridge and a three-terminal measurement method, several measurements are presented. A relative resolution of 10(-8) for the thermal expansion of samples is obtained at low temperature in a differential configuration. The same technique adopted for pressure gauge measurements at low temperature led to a typical 0.1 Pa resolution over a dynamic range of 10(4) Pa. In the configuration of interleaved electrodes, condensers have been used to measure wetting by either bulk liquid helium or by thin continuous helium films in a cylindrical pipe. Both experimental and numerical evidence is provided, showing that the close proximity of a reference ground potential significantly increases the relative sensitivity to fluid wetting. Further, interleaved electrodes can be used to access both the area that is covered by a liquid film but also to determine the thickness of this film, provided it is comparable to the periodicity of the electrode pattern.     

A low-temperature capacitive dilatometer

A dilatometer with a capacitive displacement sensor intended for measuring the thermal expansion of solid samples in a temperature range of 4–300 K is described. The sensor of the instrument was mounted inside of industrial insert VTI SIV with controlled circulation of liquid helium encased in portable cryostat and was successfully used jointly with a simple commercial temperature control system. The dilatometer allows studies of the thermal expansion of samples with a sensitivity of ∼1.4 ? in consecutive cooling and warming cycles with a rate of ∼10⁻³ K/min. The results of measuring the thermal expansion of a CoS₂ sample near the phase-transition point are presented.     

New instruments which facilitate rapid freezing at 83 K and 6 K

We have developed three instruments to freeze different biological specimens for various purposes in the easiest and most economical way: a punching device, a rapid immersion device and a device to freeze the specimens against a copper block cooled by liquid helium. Cooling rate measurements are made by a thin flat thermocouple. Freezing against a copper block cooled down to 4 K gives cooling rates 3–5 times higher than freezing by immersion into propane at 85 K.     

An improved single crystal adsorption calorimeter for determining gas adsorption and reaction energies on complex model catalysts

A new ultrahigh vacuum microcalorimeter for measuring heats of adsorption and adsorption-induced surface reactions on complex single crystal-based model surfaces is described. It has been specifically designed to study the interaction of gaseous molecules with well-defined model catalysts consisting of metal nanoparticles supported on single crystal surfaces or epitaxial thin oxide films grown on single crystals. The detection principle is based on the previously described measurement of the temperature rise upon adsorption of gaseous molecules by use of a pyroelectric polymer ribbon, which is brought into mechanical∕thermal contact with the back side of the thin single crystal. The instrument includes (i) a preparation chamber providing the required equipment to prepare supported model catalysts involving well-defined nanoparticles on clean single crystal surfaces and to characterize them using surface analysis techniques and in situ reflectivity measurements and (ii) the adsorption∕reaction chamber containing a molecular beam, a pyroelectric heat detector, and calibration tools for determining the absolute reactant fluxes and adsorption heats. The molecular beam is produced by a differentially pumped source based on a multichannel array capable of providing variable fluxes of both high and low vapor pressure gaseous molecules in the range of 0.005-1.5 × 10(15) molecules?cm(-2)?s(-1) and is modulated by means of the computer-controlled chopper with the shortest pulse length of 150 ms. The calorimetric measurements of adsorption and reaction heats can be performed in a broad temperature range from 100 to 300 K. A novel vibrational isolation method for the pyroelectric detector is introduced for the reduction of acoustic noise. The detector shows a pulse-to-pulse standard deviation ≤15 nJ when heat pulses in the range of 190-3600 nJ are applied to the sample surface with a chopped laser. Particularly for CO adsorption on Pt(111), the energy input of 15 nJ (or 120 nJ?cm(-2)) corresponds to the detection limit for adsorption of less than 1.5 × 10(12) CO molecules?cm(-2) or less than 0.1% of the monolayer coverage (with respect to the 1.5 × 10(15) surface Pt atoms?cm(-2)). The absolute accuracy in energy is within ～7%-9%. As a test of the new calorimeter, the adsorption heats of CO on Pt(111) at different temperatures were measured and compared to previously obtained calorimetric data at 300 K.     

Air gauges as a part of the dimensional inspection systems

Air gauges for dimensional measurement are known for decades. They have been applied in many technological processes, especially in the systems of in-process control. The air gauges are connected with pneumatic measuring devices able to generate control signals. Nowadays, however, it is not enough to just indicate dimensional bounds of tolerance. The Quality Management Systems require recorded and processed data achieved during the measurement. Investigations led to the development of air gauges integrated with piezoresistive pressure transducers. In those systems the results of measurement are achieved in digital form, they are processed and recorded. Additionally, dynamical properties of integrated air gauges appear much better. Multipoint linearization of the air gauge appears to be advantageous, though some companies offer the adjustment using one setting master only.     

Improvement in stage measuring technique of the ultrasonic sensor gauge

Bar check is the routine procedure in depth sounding to eliminate temperature influencing effect during the oceanographic surveying. This paper adopted the bar check concept prior to stream stage measuring on-site to improve the measuring accuracy and efficiency with popular ultrasonic sensor gauges. This study also propose both experimental dimensionless curves/corresponding equations and the relative profile of calibrating coefficients and ambient temperature of the specific ultrasonic sensor to accelerate the field calibrating process and for the bar check calibrating procedure being unavailable before the formal stage measuring. Then, field stage measuring data by a float-type gauge with which relative reliable measuring result being identified were compared with the data by an ultrasonic sensor gauge measuring simultaneously at the same location and obtained quite similar results. This advanced and improved stage measuring technique of ultrasonic sensor gauges without sonic conduit has been proved its practical validity in field stage accurate measuring throughout the on-site bar check procedure and introduced the process with dimensionless curves/formulas and relative correlation profile between calibrating coefficients and ambient temperature as well.     

Virtual spheres gauge for coordinate measuring arms performance test

This work presents a new class of gauges with virtual spheres to check the performance of coordinate measuring arms (CMA). The proposed gauge has two groups of four holes that are used to determine points of two spherical surfaces. These points are fitted to spheres using computational algorithms and the distance between the center of the spheres is calculated. The proposed gauge was named virtual ball bar and an application was performed to test the performance of an articulated arm CMA with rigid probe. The results were compared with the application of the ANSI/ASME B89 volumetric performance test using a conventional ball bar and the proposed virtual ball bar. An additional experiment using fractional factorial design was carried out to complement the comparison of the gauges. The results showed good agreement between the two approaches and it was observed a potential cost reduction compared to ball bar gauge.     

Designing of an Electromagnetic-Acoustic Thickness Gauge for Testing of Thin-Walled Pipes

A contactless electromagnetic-acoustic thickness gauge has been designed. The gauge ensures high-rate automatic contactless ultrasonic thickness measurements and makes it possible to process the information in real time, sort out the products into two classes when their thickness deviates from the permissible interval, to display the measurement results graphically in real time, and to conserve these results in the form of computer files, as well as to analyze the measurement results and output the information in the form of a report. The new thickness gauge has considerable advantages as compared with wet thickness gauges which use a contact liquid.     

Recast layer removal using ultrafast laser in titanium alloy

Recast layer, which has undesirable effects on the fatigue resistance and service life of components and microstructures, has been observed and analyzed from the points of surface morphology and internal microstructure by three test methods including scanning electron microscopy, metallographic corrosion analysis, and transmission electron microscopy in this study. In order to reduce the harms of these unwanted recast layers, taking ultrafast laser as a post-machining method for recast material removal is proposed based on the advantages of ultrafast laser micromachining technology, which include the wide material applicability and absence of the recast layer during processing. The feasibility of this new recast layer removal method was verified by experiments on Ti-6Al-4V. With a series of optimized processing parameters, horizontally bedded scanning processing was adopted ultimately in final recast layer removal experiment because of its higher material removal rate and better machined surface quality compared with vertically shifting scanning processing. Based on the theoretical analysis and experimental results, ultrafast laser could be widely applied in more fields of microstructures finish machining.     

Thermally defined cryomicroscopy and some applications on human leucocytes

A freezing-stage has been developed for use on a standard light-microscope, which can provide reproducible, precisely linear cooling and warming rates in the range from 0·1 to 10,000 K/min. Biological cells in aqueous solutions can be observed during the freeze-thaw cycle; the volume loss due to osmotic efflux of water and the intracellular crystallization of water are detected by video-monitoring. The temperature field generated in the observed samples is comparable to extended cylindrical probes and allows the transfer of cryomicroscopic data to technically used vial geometries. Lymphocytes and granulocytes were observed during freezing using the system described. They were separated and washed, and then frozen on the cold stage of the cryomicroscope at cooling rates ranging from 2 to 500 K/min. Shrinkage of the cells was observed up to 100 K/min and intracellular ice formation could be detected starting at 10 K/min. The results show that human leucocytes show excessive shrinkage up to 36% of their initial volume; the probability of intracellular ice formation exhibits a sharp increase from 10 to 100 K/min where nearly all cells contain ice.