Heat Pulse Technique Research Articles

Ballistic Propagation of Near-Gap Phonons in Bulk Superconducting Tin

Phonon transport in $\ensuremath{\beta}$-Sn crystals was studied by heat-pulse techniques using superconducting tunnel-junction detectors. The temperature-dependent attenuation by the quasiparticles was measured at fixed frequency (\ensuremath{\simeq} 160 GHz), while, at lower temperature (0.6 K), the ballistic transmission was monitored up to the onset of pair-breaking frequencies. A new method of determining the energy gap follows, which is shown to apply to nonequilibrium states of the bulk.

Heat capacity and thermal conductivity measurements down to 25 mk on samples of poor thermal diffusivity and small specific heat

A heat pulse technique is described with a permanent heat link to the cold sink used for the measurement of small heat capacities, such as vitreous dielectrics, down to 25 mK. Total heat capacities of the order of 5μJ K −1 are measured below 50 mK with an accuracy of 5%. Two carbon resistor thermometers are used to avoid any systematic error. Thermal conductivity measurements are also performed in the same temperature range by the steady flow method. The accuracy of the carbon resistor thermometer calibration enables the measurement of 2 or 3 mK temperature gradients at 25 mK.

Attenuation of second sound in He II under pressure

The propagation of second sound in He II has been studied as a function of temperature and pressure using a heat pulse technique. Considerable broadening of the pulses with decreasing temperature has been observed below 1.2 K over a range of pressures. Using an appropriate analysis, values of the velocity and coefficient of absorption of second sound have been obtained. The measurements extend to a lowest temperature of 0.75 K, below which severe attenuation precludes meaningful analysis. The results for the coefficient of absorption are compared with the theory of Khalatnikov and Chernikova.

Specific heat of Co2+, Fe2+and Mn2+perchlorates at low temperature

The temperature dependence of the specific heat of Co2+, Fe2+ and Mn2+ perchlorates have been studied using a heat-pulse technique. It is found that all three compounds have a lambda -shaped Cp against T dependence around the transition point. In addition it is shown from the analysis of the critical region data that the phase transition has a second-order origin.

Hydrodynamics of rotons below 1 °K: Theory and experiments

Using a heat-pulse technique the decoupling of phonons and rotons at low temperature in superfluid /sup 4/He under pressure (0--25 bar) is studied. It is shown that the phonons and the rotons behave as two independent fluids at low temperature. The line shapes, the time of flight, and the linewidths are in good agreement with our theory, using the Khalatnikov theory for the phonon-roton interaction and a dipole-dipole interaction between rotons. (AIP)

Specific heat of Tl2Se between 3 and 640K

The specific heat capacity of Tl2Se has been measured by applying a heat pulse technique in the temperature range 3-300K and differential scanning calorimetry in the temperature range 190-640K. The specific heat of the material can be described by Tarasov's equation for a layer structure. Values of thermodynamic functions have been calculated.

Low-temperature heat-pulse calorimetry for self-heating radioactive samples

A heat-pulse technique is described for measuring low-temperature heat capacities of radioactive self-heating samples in the range 2–60 K. The method also provides a simple alternative to traditional heat-pulse methods for measuring nonradioactive samples and is attractive because a heat switch is not required. Data for copper indicate an overall accuracy of about 1%. Heat capacity data for plutonium-242 between 4 and 13 K are also presented.

Sap Velocity Studies in Natural Stands of Pinyon and Juniper Trees

Highlight: Sap velocities in pinyon (Pin& edulis Engelm.) and juniper (Juniperus osteosperma (TOW.) Little) trees in southeastern and southwestern Utah were studied for 1 year using the heat-pulse technique. Measured velocities were related to nearby environmental factors and Dalton’s simplified aerodynamic method for estimating evaporation from water. Sap velocity was independent of the dry weight of green biomass within both pinyon and juniper trees. From 90.5 to 99.0% and from 66.0 to 99.0% of the variability in diurnal sap velocities in pinyon and juniper trees, respectively, could be accounted for by using an 8-variable multiple regression equation. Dalton’s equation accounted for 4.0 to 86.0% of the variability in diurnal sap velocities for both tree species on select days. Amount of variability in sap velocities explained by multiple regression equations was reduced markedly when sap velocities and environmental data were pooled over all sampling dates.

Heat capacity and thermal conductivity of sintered Al2O3 at low temperatures by the heat pulse technique

A heat pulse is applied at one point of a finite one-dimensional sample, the other end being clamped to a heat sink. The subsequent temperature rise at the middle of the sample is analyzed by a moments method to yield the absolute values of the thermal diffusivity, the heat capacity, and the thermal conductivity. As the method is based on pulse shape analysis, an on-line computer analysis was performed. The experimental setup was used to check the possibility of using sintered Al2O3 (ceramic) as a suitable substrate for heat capacity experiments of thin films at low temperatures.

Specific heat of CoBr26H2O in the 1-5K range

The specific heat capacity of antiferromagnetic CoBr26H2O has been measured in the 1.2-5.0K range using the heat pulse technique. The results indicate an effective spin S'=1/2 system having a lambda transition at TN=3.135+or-0.005K. The authors find that 58+or-2% of the total entropy increase is needed to reach TN compared with 49% for isomorphic CoCl26H2O. Tables of critical values and estimates of the average nearest-neighbour exchange parameters are presented. Within the limitations of an oversimplified model, it is concluded that the thermodynamics of CoBr26H2O and CoCl26H2O agree with three-dimensional Heisenberg model calculations. The best estimate of the average nearest-neighbour exchange constant is -1.6K for the bromide and -1.3K for the chloride. The greater short-range order observed for the chloride is attributed to the effect of the relatively larger intrasublattice coupling.

A mathematical method for the analysis of heat capacity and thermal conductivity measurements by the heat pulse technique

We present a new mathematical method for the analysis of heat capacity and thermal conductivity measurements by the heat pulse technique for the case of samples of finite length with a one-dimensional heat flow. In these experiments a heat pulse is produced by a heater, and the temperature is measured as a function of time at a different location on the sample. Finite length effects are taken care of in a natural way, and the thermal conductivity is obtained very simply. In addition, this method is capable of separating the heat capacities of the sample, of the heater and of the thermometer, which may be of practical importance for the case of thin samples with a small heat capacity. The mathematical analysis is based on Laplace transform techniques similar to those used for electrical transmission lines. The analysis of the experimental data is performed by calculating several moments of the temperature rise in the thermometer as a function of time. The method is particularly suitable for on-line computer experiments.

A negative heat pulse technique (for phonon studies)

A simple technique for producing a pulsed decrease of phonon populations in solids at low temperatures is described. This is not a true negative heat pulse since the prepulse situation is a steady state and not a thermal equilibrium. It is suggested that, nevertheless, the method will prove useful in some heat pulse situations, for example in the study of heat pulses interacting with paramagnetic spins.

Specific heat of thallium monoselenide between 3 and 600K

The specific heat at constant pressure of small single crystals of thallium monoselenide has been measured by applying a heat pulse technique in the temperature range 3-300K and a differential calorimetric measuring method in the temperature range 190-600K.

Velocity Spectrum of Atoms Evaporating from a Liquid He Surface at Low Temperatures

Using the heat-pulse technique, we have measured the velocity spectrum of atoms evaporating from a free liquid $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ surface. In the ballistic regime (at sufficiently low ambient temperatures) this spectrum is found to be Maxwell-Boltzmann in nature with no effects evident owing to the quasiparticle nature of the liquid. At higher vapor pressures (higher temperatures) the transition from ballistic atomic propagation to collective adiabatic sound in $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ has been studied.

A heat pulse method of measuring water flux in woody plant stems

The problem of measuring total sap flux in a woody stem by a heat pulse technique is considered for the especially simple case of a pulse which approximates a simple increasing exponential. It is shown that, for such a pulse, the total sap flux can be measured in the limits of ideal ring or ideal diffuse porosity; but it is also shown that to come sufficiently close to these limits is exceedingly difficult. It is concluded that the quantitative measurement of total sap flux by heat pulse techniques is probably too hard to be of widespread practical utility.

Three-layer thermal-diffusivity problem applied to measurements on mercury

To adapt and apply the heat-pulse technique for thermal-diffusivity measurements to liquids, the one-dimensional three-layer heat conduction problem has been solved analytically with an adiabatic boundary condition on the front surface and both adiabatic and isothermal boundary conditions on the rear surface. Computed solutions of the three-, two-, and one-layer problems are compared to determine the relative effects of the front layer (window) and the rear layer (cell material) on the temperature pulse shape transmitted through the liquid layer. Measurements at several temperatures from 294 to 267°K on a mercury specimen are analyzed using these results and the deduced diffusivity values are compared with those given by the Thermophysical Properties Research Center.

Reflection of Phonons at an Interface between a Solid and Liquid Helium

The reflection coefficient of phonons at a boundary between several dielectric crystals and liquid helium has been measured by the heat-pulse technique. The reflection coefficient is found to be smaller for transverse phonons than for longitudinal.

Thermal gantmakher resonance

A heat pulse technique is suggested as a way of measuring ωc, the cyclotron frequency. The result will be sensitive to surface scattering.

A sinusoidal heat pulse technique for the study of heat conduction in fluids

A new method for the study of heat conduction in fluids is described. The hot-wire technique used involves measurement of phase angle between temperature pulse and heat pulse for a periodic heat flux boundary condition, and is not affected by natural convection and radiation. Typical results are given on several fluids. Applications of the method are in the measure of thermal conductivities, and in the study of non-linear as well as non-continuum and relaxation effects in heat conduction.

Thermal Conductivity and Heat Capacity of the Monophosphide and Monosulfide of Plutonium

The thermal properties of PUP and PUS were measured from room temperature to 650° C by a heat‐pulse technique. Disk‐shaped specimens of 90% theoretical density were made by isostatic cold‐pressing and sintering. The thermal conductivity of PUP corrected to theoretical density ranged from 0.014 cal sec‐cm‐1°C‐1 at room temperature to 0.019 at 650° C. Over this temperature range the heat capacity increased from 0.055 to 0.056 cal g‐l°C‐1. The thermal conductivity of PUS decreased approximately 16% from its room temperature value of 0.023 cal sec‐cm‐1°C‐1 and then rose to 0.037 at 650°C. The temperature dependence of the thermal conductivity of PUP is apparently related to the quasimetallic electrical properties of this compound. PUS is a semiconductor and the rise in its thermal conductivity (after passing through a minimum) may be partly attributed to a bipolar thermal diffusion mechanism.