Authors:A. Boller, I. Okazaki, K. Ishikiriyama, G. Zhang, and B. Wunderlich
The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on the symmetry of the twin
calorimeters. This symmetry is of particular importance for the temperature-modulated DSC (TMDSC) since positive and negative
deviations from symmetry cannot be distinguished in the most popular analysis methods. Three different DSC instruments capable
of modulation have been calibrated for asymmetry using standard non-modulated measurements and a simple method is described
that avoids potentially large errors when using the reversing heat capacity as the measured quantity. It consists of overcompensating
the temperature-dependent asymmetry by increasing the mass of the sample pan.
This article presents the concept of calibrating temperature in thermomechanical analyzers (TMA) using reference standard
magnetic materials whose Curie temperatures are well-known. This concept has not been tested experimentally to the best of
the author's knowledge. Electrical current applied to a unifilarly wound furnace results in the furnace acting as an electrical
inductor. A magnetic material sample located within such a furnace practically constitutes a solenoid core. A modulated temperature
program directly results in a corresponding varying force exerted by the sample against the TMA probe, if the probe's axis
and the central induced magnetic field line of force are coaxial, and, furthermore, if the direction of the central magnetic
field line of force and the expansion direction of the probe are identical. If a sample undergoes a Curie transition, then
the force which the sample exerts against the probe will diminish to zero as the transition goes to completion. Using a modulated
temperature program throughout this phase transition allows determination of transition completion, by observation of the
point at which the force required to maintain the sample's physical position reaches a steady state from it's previously non-steady
Authors:S. Howell, R. Sigg, F. Moore, and T. DeVol
A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of 60Co and 152Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120–1400 keV. Second, a PGNAA system consisting of a light-water moderated 252Cf (1.06 g) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the 252Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 g/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model.
Radium-228 was separated from aged thorium nitrate by liquid-liquid, two-phase, extraction and extensively purified, principally
by ion-exchange chromatography. The radioactivity concentration of the purified radium-228 was measured by means of liquid-scintillation
β-particle measurements of the228Ac daughter (corrected for progeny ingrowth). The results were confirmed by Ge(Li)well-detector intercomparison with radium-228
in equilibrium with its thorium-232 precursor which had been measured gravimetrically. Three hundred ampoules were provided
to the U.S. Environmental Protection Agency, Las Vegas, for distribution.
The thermal behavior of a drawn PET fiber has been investigated by thermomechanical analysis, TMA, and by differential scanning calorimetry, DSC. Above the glass transition temperature of 79°C, the fiber shrinks to a maximum of 8% of the initial length. Temperature modulated TMA enabled the separation of the thermal expansion from the overlapping shrinkage during the first heating and to calculate the expansivity,
e and the shrinkage coefficient,
s, independent of each other. Young's modulus, E, was measured by TMA with modulation of the tensile stress. Hence, it was possible to record the behavior of
s and E during the structural changes by combining both modulations in a single measurement.A new technique was developed to calibrate the sample temperature. With this, accurate control of the modulated temperature of the specimen was achieved, independent of the changing heating rate.
Mixed gamma-ray point sources consisting of 152Eu and 154Eu were prepared from a solution of EuCl3 containing both isotopes. Gamma-rays emitted from these isotopes were used to establish the relative efficiency curves of
HPGe detector, which were converted to absolute ones using gamma-ray sources of well-known activities. Gamma-ray attenuation
correction factors were taken into account. Accuracies of activity measurements of the prepared sources were checked by measuring
other sources of well-known activities and confirmed by simulating the absolute efficiency curve at distance of 15 cm from
the detector window using the DETEFF software. The prepared sources were then submitted to quality control tests.
The addition of54Mn and65Zn to a nine-radionuclide standard (containing241Am.,109Cd.57Co,139Ce,203Hg.113Sn,137Cs,88Y, and60Co) provides the capability to determine the extent of coincidence summing for gamma rays from88Y and60Co. A method for correcting the efficiency points at 1332 keV (60Co) and 1836 keV (88Y) for coincidence summing is presented.
Silica gel suspension is electrosprayed onto the VYNS thin film to get a circular pad. The weighed -radioactive standard solution is dropped on the circle. After drying it is covered with a thin film to get a sandwich source. A new method is developed in which the -sources of high resolution and quantification are obtained. The thin film is used to avoid the contamination of -detectors used for low-level measurements.
Neutron activation analysis provides an accurate elemental assessment of body compositional compartments; the analytical technique identifies skeletal, muscle, protein, and fat masses. Our irradiator system uses 56241AmBe sources (4.4·107 n/s each) which can be arranged in four basic geometries to examine body sizes from a preterm infant (500 g, 30 cm) to a very large adult (120 kg, 2m). Both in vivo and human cadaver studies have been performed. Precisions of 1 to 2% for total body Ca, P, Na, and Cl have been obtained.