Showing papers on "Calorimeter published in 1996"

X‐ray detection using a superconducting transition‐edge sensor microcalorimeter with electrothermal feedback

Abstract: We have developed a new type of x‐ray detector based on a superconducting transition‐edge thermometer operated near 100 mK. A superconducting quantum interference device is used to measure the current through the thermometer, and negative electrothermal feedback is used to improve the energy resolution and shorten the thermal time constant. We have used a detector mounted on a scanning electron microscope to measure the energy of titanium Kα (4.5 keV) fluorescence x rays with a resolution better than 14 eV full width at half‐maximum. Using two other devices, we have measured an energy resolution for Joule heat pulses of 2.6 eV at 1 keV and 0.2 eV at 4 eV, the best reported for any calorimeter. An electrical noise equivalent power of 3×10−18 W/√Hz was also measured, suggesting the use of these detectors as infrared bolometers.

Heat capacity and thermal relaxation of bulk helium very near the lambda point

Abstract: HEAT CAPACITY AND THERMAL RELAXATION OF BULK HELIUM __ _/VERY NEAR THE LAMBDA POINTJ. A. Lipa*, D. R. Swanson*, J. A. Nissen*, and T. C. P. Chui +*Department of Physics, Stanford University, Stanford, CA.+Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA.ABSTRACTIn October 1992 a low temperature experiment was flown on the Space Shuttle in low Earth orbit.The objective of the mission was to measure the heat capacity and thermal conductivity of helium veryclose to the lambda point with the smearing effect of gravity removed. We report preliminary results fromthe experiment, and compare them with related measurements performed on the ground. The samplewas a sphere of helium 3.5 cm in diameter contained within a copper calorimeter of very high thermalconductivity. The calorimeter was attached to a pair of high resolution paramagnetic salt thermometerswith noise levels in the 10-10/( range and suspended from a high stability thermal isolation system.During the mission we found that the resolution of the thermometers was degraded somewhat due to theimpact of charged particles. This effect limited the useful resolution of the measurements to about twonanokelvins from the lambda point. The results reported here are limited to about ten nanokelvins fromthe transition.INTRODUCTIONSince the first high resolution measurements of the heat capacity singularity at the lambda point,this transition has become the most important testing ground for theories of second order phasetransitions. The transition is very sharp because of the strain-free nature of the fluid and its relatively lowcompressibility. With sample heights of the order of millimeters, values of t as small as 10-7 can bereached on Earth before intrinsic distortion is encountered. Here t = I1-T/T_,I is a dimensionlesstemperature parameter, and TX is the transition temperature. The ultimate limit in ground basedmeasurements is usually encountered when finite size effects 1 become appreciable, generally near t=5x10 "8. In space, the lambda transition may be sharp to t ~ 10"12 or so2, in optimal conditions. Since theearly 70's the aim of most high resolution experiments in this region has been to test the renormalizationgroup (RG) formalism developed by Wilson3 to predict the singular thermodynamic behavior observed inJoint "L+I" Science Review for USML-1 and USMP-1with the Microgravity Measurement Group, September22-24, 1993, Huntsville, Alabama, USA.5

Thermal analysis using a micromechanical calorimeter

Abstract: A fast and extremely sensitive method for reversible thermal analysis of picoliter volumes of solid samples is presented. Using a micromechanical calorimeter based on the deflection of a bimetallic cantilever, enthalpy changes at phase transitions in n‐alkanes (paraffins) are determined. The key role of volume changes associated with phase transitions is discussed together with a method to separate thermal and volume‐induced stresses associated with these phase transitions.

Measurement and prediction of energy transfer efficiency in laser beam welding

Abstract: The absorption of laser energy by the workpiece during laserbeam welding (LBW) has been studied through direct measurements of heat input obtained with a Seebeck envelope calorimeter. The experiment compared workpiece materials with contrasting thermal properties (304 stainless steel, 1018 steel, tin), and varied the laser power, travel speed, and focus spot size in order to determine their effects on two figures of merit : the energy transfer efficiency and the melting efficiency. An uncertainty analysis of the experimental measurements and calculated parameters has been included. The energy transfer efficiency during laser beam welding was found to increase with beam intensity from 0.20 to 0.90 and to stabilize at a high value at intensities greater than 30 kW/cm. No correlation with energy transfer efficiency was found for either the fusion zone depth-to-width ratio or the travel speed. Measured melting efficiencies for laser welding were found to be no higher than the theoretical maximum value of 0.48 which can be obtained with conventional arc welding processes. However, improved melting efficiency over conventional processes was obtained due to the shapes of laser welds that create two-dimensional heat flow in nominally three-dimensional heat flow applications. A mathematical model for laser welding has been developed using dimensionless parameters that relate the size of a laser weld to the net heat absorbed by the workpiece. Through application of this model, the energy transfer efficiency for continuous wave laser welding processes can be calculated after measurements of weld cross-sectional area have been made. Use of this model is expected to assist in optimization of laser welding for any type of material when it is used to select processing regimes that maximize melting efficiency and energy transfer efficiency.

Some enthalpies of solution of c60 and c70. thermodynamics of the temperature dependence of fullerene solubility

Abstract: The enthalpy of solution of C60 in toluene, carbon disulfide, decalin, and N,N-diethylaniline and of C70 in CS2 has been measured using an isoperibol solution calorimeter. Exothermic heats of solution are observed in all cases. The heat of solution of C60 in toluene is −8.6 ± 0.7 kJ mol-1; in carbon disulfide it is −20 ± 1 kJ mol-1. In decalin, slow dissolution prevents an accurate determination, but the heat of solution is less than −5 kJ mol-1. In N,N-diethylaniline, a fast exothermic step comparable to that observed in other systems is followed by a much larger heat evolution, implying that a chemical reaction is occurring. The heat of solution of C70 in CS2 is −9 ± 1 kJ mol-1. A thermodynamic theory of the temperature dependence of fullerene solubility is presented. The central idea is that the unusual temperature dependence of the solubilities of fullerenes is caused by the formation of solvated crystals. Conditions are derived under which a temperature maximum of solubility, caused by an incongruent...

Reproducibility of 24-h energy expenditure and macronutrient oxidation rates in an indirect calorimeter

Abstract: The maintenance of weight and adipose tissue mass in humans appears to be related to a balance between the rates of oxidation and consumption of macronutrients; yet, little evidence is available on...

Applications of calorimetry to nonelectrolyte solutions

Abstract: This paper describes the application of calorimetry to the measurement of the excess molar enthalpies for binary mixtures of nonelectrolytes. Batch, displacement, and flow calorimeters are described, using as examples the batch calorimeter of McGlashan;, the displacement calorimeters of Van Ness and of Marsh and Stokes, and the flow calorimeters of Christensen, Wormald, and Picker. Applications are described using calorimeters to measure for {(nonpolar + nonpolar), (polar + nonpolar), and (polar + polar)} mixtures. Excess enthalpies for liquid mixtures containing charge-transfer complexes and hydrogen bonds are used to help in understanding the nature of the molecular interactions in these systems. Applications involving measurements on liquid, gas, and supercritical fluid mixtures, including measurements in the near-critical region, are also described. The use of calorimetric measurements to determine {(liquid + liquid) and (vapor + liquid)} phase equilibria is discussed. Finally, equations used to repre...

Water calorimetry and ionization chamber dosimetry in an 85-MeV clinical proton beam.

Abstract: In recent years, the increased use of proton beams for clinical purposes has enhanced the demand for accurate absolute dosimetry for protons. As calorimetry is the most direct way to establish the absorbed dose and because water has recently been accepted as standard material for this type of beam, the importance of water calorimetry is obvious. In this work we report water calorimeter operation in an 85-MeV proton beam and a comparison of the absorbed dose to water measured by ionometry with the dose resulting from water calorimetric measurements. To ensure a proper understanding of the heat defect for defined impurities in water for this type of radiation, a relative response study was first done in comparison with theoretical calculations of the heat defect. The results showed that pure hypoxic water and hydrogen-saturated water yielded the same response with practically zero heat defect, in agreement with the model calculations. The absorbed dose inferred from these measurements was then compared with the dose derived from ionometry by applying the European Charged Heavy Particle Dosimetry (ECHED) protocol. Restricting the comparison to chambers recommended in the protocol, the calorimeter dose was found to be 2.6% +/- 0.9% lower than the average ionometry dose. In order to estimate the significance of chamber-dependent effects in this deviation, measurements were performed using a set of ten ionization chambers of five different types. The maximum internal deviation in the ionometry results amounted to 1.1%. We detected no systematic chamber volume dependence, but observed a small but systematic effect of the chamber wall thickness. The observed deviation between calorimetry and ionometry can be attributed to a combination of the value of (Wair/e)p for protons, adopted in the ECHED protocol, the mass stopping power ratios of water to air for protons, and possibly small ionization chamber wall effects.

The UK primary standard calorimeter for photon-beam absorbed dose measurement

Abstract: A description is given of the UK primary standard graphite calorimeter system. The calorimeter measures absorbed dose to graphite for photon radiations from 60Co to 19 MV x-rays, and is the basis of the NPL therapy-level absorbed dose to water calibration service. Absorbed dose to graphite from the photon calorimeter has been compared with three other standards: an ionization chamber and cavity theory, for 60Co gamma radiation; the NPL electron calorimeter, for 12-14 MeV electron beams; and the BIPM 60Co absorbed dose standard. The three standards agreed within 0.5% which is similar to the measurement uncertainties.

The presampler for the forward and rear calorimeter in the ZEUS detector

Abstract: The ZEUS detector at HERA has been supplemented with a presampler detector in front of the forward and rear calorimeters. It consists of a segmented scintillator array read out with wavelength-shifting fibers. We discuss its design, construction and performance. Test beam data obtained with a prototype presampler and the ZEUS prototype calorimeter demonstrate the main function of this detector, i.e. the correction for the energy lost by an electron interacting in inactive material in front of the calorimeter.

Isopiestic measurements and assessment of the Al-Pb system

Abstract: An isopiestic method was used to measure the extent of the miscibility gap of liquid Al-Pb alloys. The enthalpy of mixing of liquid aluminium and lead-rich alloys at 1125 K was measured using a high temperature mixing calorimeter. These values, together with literature data of the phase diagram and of chemical potentials, were used to calculate an optimized set of thermodynamic functions describing the thermodynamic properties of the liquid phase. The diagrams calculated from the resulting coefficient set agree very well with the experimental data.

Response to electrons and pions of the calorimeter for the CHORUS experiment

Abstract: We built and tested on charged particle beams the high energy-resolution calorimeter for the CHORUS experiment, which searches for νμ-ντ oscillations in the CERN Wide Band Neutrino Beam. This calorimeter is longitudinally divided into three sectors: one electromagnetic and two hadronic. The first two upstream sectors are made of lead and plastic scintillating fibers in the volume ratio of 4 1 , and they represent the first large scale application of this technique for combined electromagnetic and hadronic calorimetry. The third sector is made of a sandwich of lead plates and scintillator strips and complements the measurement of the hadronic energy flow. In this paper, we briefly describe the calorimeter design and we show results on its response to electrons and pions, obtained from tests performed at the CERN SPS and PS. An energy resolution of σ(E)/E=(32.3±2.4)%/ E(GeV) + (1.4±0.7)% was achieved for pions, and σ(E)/E=(13.8±0.9)%/ E(GeV) + (−0.2±0.4)% for electrons.

A calorimetric study on the configurational enthalpy and low-energy excitation of ground amorphous solid and liquid-quenched glass of 1, 3, 5-tri--naphthylbenzene

Abstract: An amorphous solid of 1, 3, 5-tri--naphthylbenzene (TNB) was prepared by grinding the crystalline sample with a vibrating mill. Heat capacities of the ground amorphous solid (GAS), liquid-quenched glass (LQG) and crystal of TNB were measured with an adiabatic calorimeter in the temperature range 10 - 330 K for the GAS and 5 - 370 K for the LQG and crystal. The heat capacities of the LQG and GAS were 0.5 - 1% larger than that of the crystal. The heat capacity of the GAS agreed with that of the LQG between 30 and 330 K but was 1 - 4% larger than that of the LQG below 30 K. The heat capacity difference in the low-temperature region can be attributed to the difference in low-energy excitation which is known as a universal property of amorphous materials. A glass transition occurred at 342 K for the LQG. For the GAS, however, a large exothermic effect due to crystallization appeared from 315 K, which is 25 K lower than of the LQG. The configurational enthalpy of GAS determined from the enthalpy of crystallization was much larger than that of the LQG. This result indicates that the structure of the GAS is much more disordered and strained than that of the LQG.

Application of low temperature calorimeters for precise Lamb shift measurements on hydrogen-like very heavy ions

Abstract: The precise determination of the 2s12, 2p12, 2p32 → 1s12 X-ray transitions in hydrogen-like very heavy ions such as 208Pb81+ or 238U91+ provides a sensitive test of QED, especially of higher order contributions to the self-energy which are not accessible by alternative methods. Such measurements became possible recently by X-ray spectroscopy using highly charged ions stored and cooled in heavy ion storage rings. A better energy resolution of the X-ray detector is most essential in order to improve the experimental accuracy, which is presently about one order of magnitude worse than the theoretical uncertainty. An energy resolution of ΔE = 30–50 eV for Eγ = 50–100 keV, and a photopeak efficiency above 30% may be provided by a low temperature calorimeter. It will be constructed on the basis of already existing arrays of silicon microcalorimeters, but with larger volume and high Z absorbers. Such a detector will allow a more precise determination of the 1s-Lamb shift and for the first time the direct investigation of the 2s-Lamb shift in hydrogen-like heavy ions. In the present contribution the experimental scenario for QED experiments at storage rings, the present status of experimental and theoretical investigations and the design of an appropriate low temperature detector are discussed.

Thermal hazard assessment and macrokinetics analysis of toluene mononitration in a batch reactor

Abstract: The thermal hazard assessment of toluene nitration in a batch reactor is implemented systematically using an isothermal reaction calorimeter in conjunction with micro-thermal calorimeters. The value of the heat of reaction is determined using calorimetric data, and the kinetic parameters for the desired reaction are derived from the isothermal self-heat rate vs time profiles. A series of safe operation limits are calculated. Results indicate that the desired reaction has a high potential to trigger a thermal explosion, caused by the decomposition of mononitrotoluene. By following these safe operation limits, suppression or elimination of the hazard potential is possible.

A linear low power remote preamplifier for the ATLAS liquid argon EM calorimeter

Abstract: In a previous paper (Nuc. Inst. Meth. vol.A330, p.228, 1993), it was shown that, for shaping times of the order of the transmission line delay, a remote, external preamplifier could perform as well as one connected directly to a liquid argon calorimeter. Here we describe an improved circuit configuration where, by attributing the functions of low noise and high dynamic range to two different transistors, the linearity can be improved and the noise can be decreased while reducing the power dissipation by a factor of three (to about 40 mW). The gain (i.e., the transresistance) and the input impedance can be chosen independently without changing the power supply voltages and power dissipation.

The WiZard/CAPRICE silicon-tungsten calorimeter

Abstract: A silicon-tungsten calorimeter has been developed to be flown in the Wizard/CAPRICE balloon borne experiment to measure the flux of antiprotons, positrons and light nuclei in the cosmic radiation. The calorimeter is composed of 8 .r. .v silicon sampling planes [active area (48 X 48) cm’] interleaved with 7 tungsten absorbers (7 radiation lengths): it provides the topology of the interacting events together with an independent measurement of the deposited energy. Details of the front-end electronics and of the read-out system are given and the overall performances during pre-flight ground operations are described as well.

The Presampler for the Forward and Rear Calorimeter in the ZEUS Detector

Abstract: The ZEUS detector at HERA has been supplemented with a presampler detector in front of the forward and rear calorimeters. It consists of a segmented scintillator array read out with wavelength-shifting fibers. We discuss its desi gn, construction and performance. Test beam data obtained with a prototype presampler and the ZEUS prototype calorimeter demonstrate the main function of this detector, i.e. the correction for the energy lost by an electron interacting in inactive material in front of the calorimeter.

The performance of a variable-flow indirect calorimeter

Abstract: Indirect calorimetry estimates energy expenditure from measurement of respiratory gas exchange volumes. This paper considers the design and evaluation of an indirect calorimeter, the Europa GEM, suitable for use in nutritional research. The calorimeter is of the ventilated hood, flow-through type and is intended for use with spontaneously breathing patients. Our aim was to develop an accurate, flexible instrument with a high level of automation. Performance was assessed in a laboratory simulation using reference gas injections (n = 24) producing a mean error of in oxygen consumption (), in carbon dioxide production () and in respiratory quotient (RQ). In order to investigate the effect of on error multiplication a further subdivision (n = 8) of tests at , 0.75% and 1% was made by modulating the air flow through the hood. However, the predicted increase in system accuracy with increasing was not apparent in practice. Keywords: indirect calorimetry, metabolism, nutrition, gas exchange

Actively cooled calorimeter measurements and environment characterization in a large pool fire

Abstract: Quasi-steady-state heat fluxes absorbed on the calorimeter surface in ten vertical 0.1 m high x 1 m wide zones were measured by means of water calorimetry. The calorimeter surface also included an array of intrinsic thermocouples to measure surface temperatures, and an array of Schmidt-Boelter radiometers for a second, more responsive, method of heat flux measurement. The pool fire environment characterization was done with measurements from velocity probes, directional flame thermometers (DFTs), and thermocouples. The initial measurements with a 1 m x 1 m water cooled vertical flat plate calorimeter located 0.8 m above and inside a 6 m x 6 m JP-4 pool fire are described. Water calorimetry measured absorbed surface heat fluxes of about 65-70 kW m -2 with a gradual decrease with increasing height above the pool. Intrinsic thermocouple measurements recorded typical calorimeter surface temperatures of about 500°C, with spatial variations of ±150°C. Gas velocities across the calorimeter face averaged 3.4 m s -1 with a predominant upward component, but with an off-vertical skew. Analysis of data collected in the fire environment in the vicinity of the calorimeter was performed to characterize the fire environment and to determine the input parameters required to calibrate analytical models. For this test, the emissive power distribution near the plate was essentially linear. Flux measurement in the fire environment ranged from 75 kW m -2 to 175 kW m -2 . With temperature and heat flux data, effective absorption coefficients were determined by using a two-flux method to solve the inverse problem. The results show that the optical thickness, increases with increasing distance from the calorimeter surface. The effective absorption coefficient is approximately 0.8 m -1 in the vicinity (0-1.85 m) of the calorimeter and is approximately 2 m -1 in the vicinity (1.85-2.8 m) of the plume centerline The observed decrease in heat flux on the calorimeter surface with increasing vertical height is consistent with analytical fire models derived for constant temperature surfaces. Results from several diagnostics also indicated trends and provided additional insight into events that occurred during the fire. Some events are correlated, and possible explanations are discussed.