High Resolution Vacuum Calorimeter

Calibrating a gas chromatograph to measure tritium using calorimetry

“…To accurately determine the tritium amount in the sample its activity has to be measured with a device independent from the GC. This measurement is carried out with a calorimeter, which measures the decay heat of tritium (0.324 ± 0.001 W/g [3]). Calorimetry is chosen because its resolution is better than 0.5 W [3].…”

“…This measurement is carried out with a calorimeter, which measures the decay heat of tritium (0.324 ± 0.001 W/g [3]). Calorimetry is chosen because its resolution is better than 0.5 W [3]. After the calorimetric measurement, the concentration of the gas (activity per volume unit) is calculated, and the gas is used as a standard to calibrate a GC.…”

“…The structure and principles of operation of such a device are described in [3], here only a short description is given. The sample vessel volume of the device used in this study is 25 l. The precision of the device for the activities of the calibrating mixtures is better than 0.1% (except one case, with a very low activity, see in Chapter 3).…”

“…Among the analytical methods gas chromatography (GC) has been proven to be advantageous, mainly because its capability to measure several kinds of gases, its low costs and the simple structure of the gas chromatographs compared with other devices. Quadrupole mass spectrometers are not readily capable to distinguish between 3 He and T, therefore cannot achieve a full determination of the isotopic composition of Q 2 mixtures (Q stands for H, D, or T). These are the reasons why GCs are widely used and are selected to be the main analytical devices in the ITER Analytical System [1].…”

TheC14(n,γ) cross section between 10 keV and 1 MeV

“…The use of this technique was favored by the comparably low β − end point energy of E max = 156 keV and by the fact that 14 C decays without emission of γ -rays. The measurement was carried out at the Tritium Laboratory of Forschungszentrum Karlsruhe [26], yielding a heat production of 370 ± 4 µW. Adopting an average energy E avg = 49.475 keV [27] for the decay electrons and a half-life of t 1/2 = 5700 ± 30 yr [20], the measured decay heat corresponds to an activity of 1.26 ± 0.01 Ci or a total mass of 283 ± 3 mg of 14 C. This value is independent of the isotopic enrichment (which was quoted to be 89%) and more than a factor of two less than the specified value, which had been wrongly adopted in the previous activation [12].…”