Gas proportional counter

The concentration of is determined by measurement of the specific P-activity. Usually, the carbon from the sample is converted into a gas, eg, carbon dioxide, methane, or acetylene, and introduced into a gas-proportional counter. Alternatively, Hquid-scintiHation counting is used after a benzene synthesis. The limit of the technique, ca 50,000 yr, is determined largely by the signal to background ratio and counting statistics. 

Tritiated or " C-tagged hydrocarbons (including tritium gas) can be measured by using a liquid scintillation counter or a gas proportional counter [1717,1718]. 

The spectrometer is set to the appropriate Bragg angle 0 of the requisite characteristic wavelength, and only these X-rays will reach the detector and be counted. The detector employed is the gas proportional counter, which can operate at much faster count rates than the EDS crystal detector. 

Electronic noise, identified via rise-time characteristics, shown rising to 30 times background rate for 15-mL gas proportional counter. A tiny fraction of such noise, not identified by means such as pulse shape analysis, could invalidate results which presume that the background is stable to < 10%. 

A detailed procedure for combustion, purification, and filling of the small gas proportional counters may be obtained from the Brookhaven authors. Since the apparatus for combustion had a maximum capacity of 10 grams it was necessary to burn three samples of Frobisher iron in order to get enough carbon dioxide to fill the counter. The carbon dioxide from the three samples was... 

An Internal Gas Proportional Counter for Measuring Low Level Environmental Radionuclides... 

The detector of choice for the efficient detection of 14-KeV y-rays is the gas proportional counter with a (mostly) krypton filling. (Methane, which we use, or carbon dioxide are typically added in a concentration of ca. 10% for quenching secondary discharges.)... 

Carbon-14 content is measured by specially designed gas proportional counters (7. Aerosol samples are first converted to CO2 by combustion in a macroscale version of the thermal evolution technique. A clam shell oven was used to heat the sample for sequential evolution of organic and elemental carbon under equivalent conditions. Due to the possibility of thermal gradients, conditions in the macroscale apparatus were adjusted to produce the same recoveries of total carbon (yg C per cm of filter area) as for the microscale apparatus. Carbon-14 data are reported as % contemporary carbon based on the 1978 1 C02 content in the atmosphere. Aldehyde data referred to in this paper were obtained by impinger sampling in dinitrophenylhydrazine/acetonitrile solution and analysis of the derivatives by HPLC with UV detection (12). Olefin measurements were made by a specially designed ozone-chemiluminescence apparatus (13) difficulties in calibration accuracy and background drift with temperature limit its use to inferences of relative reactive hydrocarbon levels. 

The three most commonly used detectors are the gas proportional counter, the scintillation detector and solid-state detectors (Pecharsky and... 

A gas proportional counter with an anticoincidence shielding counter has also been utilized. Ethane gas is commonly used as a counting gas. A water sample is reduced to hydrogen gas using Mg or Zn powder in a furnace. Hydrogen gas thus produced is added to dead ethylene or acetylene gas with a Pd catalyst to form ethane-counting gas. 

Lunar Prospector s two most important geochemical mapping sensors were designed for gamma-ray spectrometry (GRS) and neutron spectrometry. The neutron spectrometer, a matched pair of He gas proportional counters, was mainly designed to map the global... 

Figure 2.17. The schematics of the gas proportional counter (left) and the scintillation (right) detectors of x-rays.

Gas proportional counters have relatively good resolution, so the heights of current pulses can be analyzed and discriminated to eliminate pulses that appear due to Kp photons and due to low and high energy white radiation photons. The pulse height discrimination is often used in combination with a p-filter to improve the elimination of the Kp and white background photons. 

A position sensitive detector (PSD) employs the principle of a gas proportional counter, with an added capability to detect the location of a photon absorption event. Hence, unlike the conventional gas proportional counter, the PSD is a line detector that can measure the intensity of the diffracted beam in multiple (usually thousands) points simultaneously. As a result, a powder diffraction experiment becomes much faster, while its quality generally remains nearly identical to that obtained using a standard gas proportional counter. ... 

The scintillation counter (Sec. 7-7) and the sealed gas proportional counter (Sec. 7-5) are both used in spectrometry. The scintillation counter is better for the very short wavelength region because of its greater efficiency there (Fig. 7-12) in the 1 A-2 A range either counter is suitable. In the long-wavelength region a gas-flow proportional counter is required, because of its thin low-absorption window. 

Resistive anode position readout systems have been used extensively in applications with MCP s and gas proportional counters (78-91). The anode consists of a resistive coating (several 100 kft) applied to an insulating substrate, ensuring that the coating resistivity is uniform. A simple one dimensional readout can take the form of a rectangular sheet with contacts at opposite ends, and a simple two dimensional readout can be a square sheet with contacts at the corners. A particular advantage of resistive anode readouts is the small number of amplifiers required only four amplifiers are required for full 2 dimensional imaging. These anodes are usually mounted close (< 1 mm) behind the MCP output face. 

GPC (total radioactive strontium) = beta gas proportional counter Bq = Becquerel dpm = disintegrations per minute EDTA = ethylenediamine tetraacetic acid GFAAS (total strontium) = graphite furnace atomic absorption spectroscopy ICP-AES (total strontium) = inductively coupled plasma atomic emission spectroscopy ICP-MS (isotopic strontium composition) = inductively coupled plasma-mass spectrometry LSC (isotopic quanitification of 89Srand 90Sr) = liquid scintillation counting pCi = pico curies (10-12 curies) PIXE (total strontium) = proton induced x-ray emission TMAH = tetramethylammonium hydroxide TNA (total strontium) = thermal neutron activation and radiometric measurement TRXF (total strontium) = total-reflection x-ray fluorescence... 

P-GPC (total radioactive strontium) = beta gas proportional counter EDTA = ethylenediamine tetraacetic acid FAAS (total strontium) = flame atomic absorption kj... 

Energy distributions in gas proportional counters— whether gas flow or sealed counters— undergo a noticeable shift to lower energies when X-ray counting rates (and, concomitantly, detector gas ionization rates) increase. The exact origin of this phenome-... 

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