Gas counters

It was found that that in the case of soft beta and X-ray radiation the IPs behave as an ideal gas counter with the 100% absorption efficiency if they are exposed in the middle of exposure range ( 10 to 10 photons/ pixel area) and that the relative uncertainty in measured intensity is determined primarily by the quantum fluctuations of the incident radiation (1). The thermal neutron absorption efficiency of the present available Gd doped IP-Neutron Detectors (IP-NDs) was found to be 53% and 69%, depending on the thicknes of the doped phosphor layer ( 85pm and 135 pm respectively). No substantial deviation in the IP response with the spatial variation over the surface of the IP was found, when irradiated by the homogeneous field of X-rays or neutrons and deviations were dominated by the incident radiation statistics (1). 

The pressure is higher at the bottom of the sohds draw-off pipe due to the relative flow of gas counter to the sohds flow. The gas may either be flowing downward more slowly than the solids or upward. The standpipe may be fluidized, or the solids may be in moving packed bed flow with no expansion. Gas is introduced at the bottom (best for group B) or at about 3-m intervals along the standpipe (best for group A). The increasing pressure causes gas inside and between... 

Solid-state detectors based on silicon- or germanium-diodes possess better resolution than gas counters, particularly when cooled with liquid nitrogen, but they allow only very low count rates. PIN diodes have also recently become available and have been developed for the instruments used in the examination of Martian soils (Sects. 3.3 and 8.3). A very recent development is the so-called silicon-drift detector (SDD), which has very high energy resolution (up to ca. 130 eV) and large sensitive detection area (up to ca. 1 cm ). The SNR is improved by an order of magnitude compared to Si-PIN detectors. Silicon drift detectors may also be used in X-ray florescence spectroscopy, even in direct combination with Mossbauer spectroscopy (see Sects. 3.3 and 8.3). 

As pointed out previously, controlled degradation reactions are very difficult with aliphatic or alicyclic hydrocarbons, and most of the relabeling work has been concentrated on aromatic reaction products. Procedures have been extensively described by Pines and co-workers (e.g., 97, 96, also 87, 89-98, 95, 98). For the present purpose, it suffices to note that the 14C contents of the methyl side-chains and the rings in aromatic reaction products are readily estimated by oxidation of the methyl to carboxyl, followed by decarboxylation, while ethyl side-chains may be oxidatively degraded one carbon atom at a time. Radiochemical assays may be made on CO2 either directly in a gas counter, or after conversion to barium carbonate, while other solid degradation intermediates (e.g., benzoic acid or the phthalic acids) may be either assayed directly as solids or burned to CO2. Liquids are best assayed after burning to CO2. 

The difficulties include the inconvenience of handling radioactivity and the necessity for obtaining an accurate radiochemical analysis of two phases containing several elements (which often involves complicated spectra). Highly sensitive instrumentation is required for the analysis e.g. a Li-Si surface barrier detector for a particles, a 2 r gas counter for (3-radiation and a Li-Ge detector for 7-radiation. Great care is required during source preparation, which is best done by electrodeposition. 

Details are given of the interaction between the macrostructure and morphology of PP structural foam mouldings made by the gas-counter pressure process. The morphology, orientation, and processes ofnon-isothermal... 

The manufacture of products, e.g. containers and lids, made from filled foamed PE by gas counter pressure injection moulding was studied with special reference to the effect of production conditions on dimensional stability. Results obtained are discussed and evaluated. 7 refs. 

Collection of a spectrum relies on the ability of the detector to recognise the energy of each of the emitted photons. This particular detector, installed close to the sample to collect part of the X-ray fluorescence, is either a proportional gas counter (neon)... 

In recent years, several developments have generated new possibilities in liquid scintillation counting. The most important event was the development of the bialkali photomultipliers with considerably improved quantum efficiency. In addition, several new scintillators and solvents of higher purity have become available. With the resulting counting systems it has been possible to achieve sensitivities comparable with gas counters, with much less time and effort involved. 

Some of the results of BFM experiments by Waldmann and Schmitt [11] cannot be explained with the DGM. These experiments are similar to the classic experiments by Kramers and Kistemaker [12] on gas counter-diffusion in a capillary, but Waldmann and Schmitt conducted experiments for a broader range of gas pairs. The experimental setup is shown schematically in Figure 9.10. It basically consists of two chambers of 64.2... 

Gaseous samples are preferably measured in ionization chambers (a radiation), proportional counters or Geiger-Muller gas counters. The samples are introduced into the counters or passed through with a gas stream (flow counters). 

Information about details of various chemical reactions can be obtained by application of radiotracers. The photographic process may be mentioned as an example if a thick cylindrical pellet of Agl is labelled on one side by isotope exchange with I, arranged in such a way that light has no access to the labelled side, and irradiated on the opposite side by visible light, l-labelled iodine is immediately liberated. It may be carried away by a stream of an inert gas and measured continuously in a gas counter. The immediate liberation of h is due to fast transport of defect electrons in Agl, in agreement with the proposed mechanism of the photographic process. 

Apparatus. The following apparatus was utilized for this study a PRT 2000 type potentiostat (Tacussel) for the electrolysis a Graphi-spectral spectrophotometer (Jouan) for the absorption measurements a TS 6 type millivoltmeter (Tacussel) for potentiometric analysis a 2ir windowless flow gas counter (S.A.I.P.) for measuring the soft beta from and a bell type Geiger counter for Ge and Ge beta counting. 

It was a biophysicist, deVries (1958), who first clearly demonstrated that the radiocarbon timescale was imperfect, i.e., that radiocarbon years were not identical to calendar years. Fascinated by the potential of Libby s new method, this brilliant Dutch scientist plunged into all its aspects. deVries devised means to reduce the background of gas counters by greatly increasing the effectiveness of the shielding from cosmic ray mesons. Not only did he strive to extend the method... 

Ruidization is common in materials that contain a significant percentage of particles smaller than 100 pm (50). Fluidization segregation is likely to occur when fine materials are pneumatically conveyed when they are filled or discharged at high rates, or if gas counter-flow occurs. As with most segregation mechanisms, the more cohesive the material, the less likely it will segregate by this mechanism. 

Fig. 7-14 Gas counter (proportional or Geiger) and basic circuit connections.

The result is the lithium-drifted silicon counter sketched in Fig. 7-20. The crystal is virtually all intrinsic, with the p and n portions confined to thin surface layers, which are exaggerated in the drawing. The very small pulses from the counter are amplified to the millivolt level by a field-effect transistor, abbreviated FET. (There is no charge amplification, such as occurs in a gas counter. The pulse from the counter contains only the charge liberated by the absorbed x-rays.)... 

This type of detector is one of the oldest and most often used in X-ray diffraction. Its response time is extremely low (= 0.2 pS). This feature is its main advantage compared to proportional gas detectors. It is sensitive to the energy of X-rays but has a poor energy resolution. Its efficiency is almost 100%. Compared to proportional gas counters, the background noise is more significant and scintillating crystals deteriorate in a humid atmosphere. 

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