Parallel-plate avalanche

An interesting variant of a CEMS counter is the parallel-plate avalanche counter (PPAC) [18, 19], which carries the sample between parallel electrodes made of Perspex coated with graphite (Fig. 3.8, left). A counter gas is used to amplify the low conversion-electron current emitted by the sample, with an avalanche effect taking place between the plates. Compared with the CEMS proportional counters, PPAC gives a larger signal-to-background ratio, faster time response, simpler construction, and better performance at low temperatures. 

Fig. 2. Experimental setup for the kinetic energy experiment. The PSC solenoid provides an axial magnetic field of 5 Tesla. PPAC Parallel plate avalanche chamber. MCP MicroChannel plate. The photomultipliers and light-guides coupled to the Csl and plastic scintillators are not shown...

The spectrograph is equipped with two position-sensitive parallel-plate avalanche counters for the detection of fission fragments in coincidence with proton ejectiles registered hy a light-ion focal plane detector (Zanotti et al. 1991). 

A gas-filled resonance counter had been set up, e.g., by installing enriched Fe stainless steel foils in a He gas chamber or parallel plate avalanche gas counter by Mullen and Stevenson (1978). An extremely Kght detector (K2Mg Fe(CN)e in Poly-Vinyl-Xylene scintillator) has also been developed for a movable resonance counter (Budakovski et aL 1999) to replace heavy... 

The remainder of this chapter is organized as follows. The next section describes some experimental and application investigations of in-beam Mossbauer spectroscopy using a Mn beam at the RIKEN RIBF. The system used for detecting Mossbauer 7-radiation in in-beam experiments is important. Nagatomo et al. [32] have recently developed a highly sensitive resonance counter based on parallel-plate avalanche and plastic scintillation counters. A new anticoincidence detection system is introduced. Finally, the experimental setup for online Mossbauer spectroscopy using the thermal neutron capture reaction, Fe (n, 7) Fe, and the results obtained are presented in the subsequent section. 

It is anyway interesting to compare data obtained from transmission experiments, ICEMS experiments using a gas electron counter (in the cases described below, a parallel plate avalanche counter v/as used), and ILEEMS experiments using the system depicted in Fig. 22.5. 

In addition to the proportional counters, other types of gas-filled detectors are used in CEMS. Eirst was the parallel-plate avalanche counter. In Mossbauer spectroscopy such detectors have been used as resonance detectors and at higher counting rates. These counters have found application in surface studies and are the effective tool for the registration of low-energy ( < 1 keV) electrons, which are practically impossible to detect with the proportional counter. Because of the high electron-detection efficiency this enables the measurement of reasonable spectra in a relatively short time for Ee,... 

Electron spec- Magnetic Parallel-plate avalanche... 

Weyer G (1976) Applications of parallels-plate avalanche counters in Mossbauer spectroscopy. In Gmverman IJ and Seidel CW (eds) Mossbauer Effect Methodology, Vol 10, pp 301-320. New York Plenum Press. 

If ocj/p data from the gas phase are converted into oc /N data and hypothetical oc /Niiq values are inserted in Equation 109 it turns out that extremely small distances d of the order of im are sufficient to fulfill the breakdown condition. From these considerations it is apparent that conditions characteristic of a Townsend avalanche are only met over very short distances. Therefore, measurements of require either, in the case of a parallel plate electrode geometry, a short electrode separation or confinement of the avalanche to the vicinity of a thin wire, a sharp blade, or tip. In the... 

Lenoble et al. (2005) studied a suspension of heavy particles at an initial solid fraction of ( ) = 0.59, a mixture they in fact termed a "wet granular material," in a simple shear flow configuration (between parallel plates) and found a sheared layer over a static layer. Granular avalanche flows under liquid have also been studied to determine the normal stress response, specifically through the pore pressure at the base of the flow (Cassar et al. 2005), and a model for the development of the steady state in such flows was presented by Pailha and Pouliquen (2009). 

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