Helium measurements

The material is, after preparation and possible activation, i. e. degassing at elevated temperatures, put in a vessel of known volume (Vac) which after evacuation is filled with a known mass (mne) of Helium gas. Assuming 

Here Phc = PHe(P T) is the density of the helium gas which can be determined from measured data of pressure (p) and temperature (T) normally by using the ideal gas equation of state (EOS) or a standardized real gas EOS [1.45]. 

This procedure is simple and effective and several types of He-gas pycnometers are commercially available, cp. Tab. 1.5. 

However, it does have certain disadvantages which may lead to serious experimental errors in gas adsorption measurements [1.46-1.49]. This will be demonstrated by a set of helium gas expansion experiments performed at the Institute of Fluid- and Thermodynamics (IF l) at the University of Siegen, Siegen during 1994 - 2002 as follows. 

Determination of the volume of activated carbon Norit R1 Extra by helium expansion measurements at 298 K in a commercial gas pycnometer (Micromerites, Accu Pyc 1330). 

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The positron-helium measurements of Mizogawa et al. (1985) were deemed to have small errors arising from positron spiralling, because of the use of low magnetic fields and the attendant limits on the transverse kinetic energy imposed by physical apertures in the system. 

This was the first occasion when so large a value was given, based too on evidence of a reliable character for Rutherford had determined the amount of uranium and radium in the rock, calulated the annual output of alpha particles, was confident that these were helium, measured the amount of helium in the rock and by simple division found the period during which the rock had existed in a compacted form. 

Exercise 14.3 How can the radiogenic helium be sorted out of the total helium measured in a sample ... 

Leaks in medical sources and seeds are detected by a vacuum immersion leach test. Because the internal volume of the medical sources is so small (3.6 x 10 mL, in the case of the ALC-P4C seed), the conventional helium leak test is not a valid leak test procedure. About 45 minutes is required to pump down the system before helium measurement is begun. If the internal volume of the test specimen is small, trapped helium would escape before helium assay begins. Therefore, leaks in encapsulated medical sources are detected by measuring the alpha activity of a nitric acid penetrant solution in which the source had been immersed. After immersion, pressure above the liquid is decreased to 2.5 psia for 3 min before venting to atmosphere. This procedure is repeated twice, then the sources remain in acid a minimum of 16 h at 20°C. 

Precision spectroscopy of two-electron atoms tests fundamental relativistic and quantum-electrodynamic atomic theory. Additional current interest in heliumlike ls2p P fine structure stems from the possibility of obtaining the fine structure constant, a, from comparison of theory [1,2,3] and experiment [4,5,6,7,8,9] for the fine structure of helium. Measurements in moderate Z ions, though less precise than those in helium, can be more sensitive to higher-order relativistic and QED corrections. Measurements have been carried out using laser techniques in Li+, see e.g. ref. [10], Be + [11], [12], N + [13,14], and F + [15,16]. For... 

What would be the volume of helium, measured at STP, generated from the decay of the Be sample in Exercise 56 ... 

The cluster Na/" also has isotropic parameters with (g) = 1.9976 and (A> = 2.9 mT or 82 MHz. This is explained as a tetrahedral cluster. The 4 3s orbitals span the representations and tj. Of the two possible configurations, aiH2" and ai, the former is in agreement with the ESR parameters and the room temperature spectral observations. Thus, the cluster is written as Na/ with groundstate Aj. Na4 is discarded because the groundstate T2 is subject to a Jahn-Teller effect and ESR spectra will probably only be observed at low temperature. Again, liquid Helium measurements are necessary to proof unambiguously our conclusions. 

A helium-mercury displacement method is sometimes used to check the pore volume obtained from the adsorption-desorption isotherm at the saturation pressure (Ries, Van Nordstrand, Johnson, and Bauer-meister, 50). The helium measurement which gives the solid volume and solid density is obtained by means of a miniature isotherm type apparatus. This part of the determination is essentially the same as that described by Smith and Howard (58) and Schumb and Rittner (55). Mercury displacement yields the pellet volume and pellet density and is measured volumetrically by means of a mercury buret attached directly to the same sample bulb in which the helium measurement is performed. The difference between the pellet volume and the solid volume is obviously the pore volume. 

On deay one atom of the radium isotope emits one a particle which forma an atom of helium gas, A sample of produced 4.48 X 10 dm of helium measured at 273 Kond 1 atm (1.01 x 10 Pa) pressure, in a given time. 

Fleischmann and Pons were actually the first to observe the production of helium-4 in the Pd/D system [4]. However, due to the extensive criticism of their 1989 announcement, they did not want ... to open another front for attacks on their work, and so their measurements of helium-4 were never officially reported. The first reported experiments correlating the calorimetric excess enthalpy and helium-4 production were conducted by Miles in 1990 at the Naval Weapons Center (now NAWCWD) in China Lake, California, and the helium measurements were performed under the supervision of Bush at the University of Texas [6-8]. The presence of helium-4 was observed in eight out of nine effluent gas samples collected during the presence of excess heat [7,8]. No helium-4 was observed for six out of the six samples of effluent gas for a Pd/H20 control study. Measurements were also conducted for heUum-3 in these studies, but none was detected [6]. In summary, for all experiments conducted by Miles at NAWCWD, 12 out of 12 produced no excess helium-4 when no excess heat was measured, and 18 out of 21 experiments gave a correlation between the measurements of excess heat and helium-4 [8, 18]. Three of the experiments that produced hehum-4 were conducted under double-blind rules [8, 18]. An exact statistical treatment for all experiments shows that the probability is only one in 750 000 that the China Lake set of heat and helium-4 measurements could be this well correlated due to random experimental errors [18]. Furthermore, the rate of helium-4 production was always in the appropriate range of 10 to 10 atoms per second per watt of excess power for D -I- D or other likely nuclear reactions [8,18]. 

This relation allows one to calculate the Gibbs surface excess (mQE) from mass and density measurements of the sorptive gas (m, p, p ) and accompanying helium measurements leading to calibration parameters (mHe.PHe). Details of the experimental procedure by volumetric / manometric measurements and several examples will be given in Chap. 2. 

If (m ) has been determined from helium measurements and (Am ,) is known from calibration measurements with a dense, i. e. non-adsorbing loading material in the bowl, can be calculated from lrot via (5.47). 

He m volume of a sorbent material determined by (low pressure, high temperature) helium measurements... 

Shen Z, Briens C, Kwauk M, Bergougnou M. Improved thermal conductivity detector technique for helium measurements in a fluidized bed. Powder Technol 69 249 253, 1992. 

The alpha particles emitted in the radioactive decay of radium-226 can be counted by means of a Geiger counter. Each alpha particle (helium nucleus) gains electrons to form helium gas. It is found that 1.82 x 10 alpha particles give 6.75 x lO cm of helium, measured at standard temperature and pressure (STP). 

A collapsible balloon for canying meteorological testing instruments aloft is partly filled with 626 liters of helium, measured at 25°C and 756 ton. Assuming the volume of the balloon is free to expand or contract according to changes in pressure and temperature, what will be its volume at an altitude where the temperature is —58°C and the pressure is 0.641 atm ... 

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