Gas-flow Proportional Counter Research Articles

K X-ray yields from elements of low atomic number

Absolute measurements have been made of the K X-ray quantum yields resulting from electron bombardment of solid targets, containing the elements beryllium, boron, carbon, oxygen, fluorine and aluminium. Beryllium oxide and lithium fluoride targets were used for the oxygen and fluorine measurements, respectively; targets containing at least 99% of the pure element were used for the remainder. The yield from each target was measured along a path inclined at 45° to the surface and at several electron accelerating voltages in the range 500 to 30 000 V ; the electron beam was then inclined at an angle of 45° to the surface of the target. The carbon yield was also measured at 10° to the surface with the electron beam inclined at 80° to the surface. The gas-flow proportional counter was operated at atmospheric pressure with a nitro-cellulose window; the window used for detecting beryllium and boron radiation was less than 1000 Å thick. The relative variation of the X-ray yield with the electron accelerating voltage is in excellent agreement with Archard’s (1960) predictions for the yield measured both at 45° and 10° to the target surface but with the electron beam normal to the surface. The absolute yield values, apart from those for beryllium, are 5 to 15% higher than those calculated from Archard’s theory and Burhop’s (1952) fluorescence yield formula; the beryllium yield is about half that predicted. For 5 ≤ Z ≤ 9, the greatest X-ray yield at 45° to the target surface is obtained when the accelerating kilovoltage is between 0.5 ( Z — 1) 2 and 0.6 ( Z — 1) 2 and amounts to 9 x 10 13 Z 5/2 photons per incident coulomb per steradian (1.45 x 10 -5 Z photons per incident electron per steradian).

New Design for a Gas-Flow Proportional Counter

This paper describes a compact design for a gas-flow proportional counter. Externally adjustable end plates for correcting the electric field allow pulse-height distribution curves comparable with those from long counters, although the counting volume is 1¼ in. in diameter and 1116 in. long. A transistorized preamplifier inside the counter case provides clear pulses with low background in a low impedance line. The gas-flow proportional counter described here has three significant features: (1) low noise, approximately 1% of the Fe Kα pulse height; (2) low impedance output from the first preamplifier; (3) energy spread less than 20%, in spite of short length and large diameter.

THE HALF-LIFE OF Ca41

Ca41, a nuclide decaying by orbital electron capture, has been again identified and its half-life measured. The activity of the source, a highly irradiated sample of calcium carbonate, had decayed for 10 years so that competing activities were non-existent. The measurement was made with a gas-flow proportional counter with well-determined characteristics. A value of (7.5 ± 1.1) × 104 years has been obtained.

Increase of Pulse Height in a Proportional Counter by Means of a Radial Thermal Gradient

BS>A gas-flow proportional counter, containing 90% Ar10% methane, showed a pulse-height increase by a factor of about ten when the central wire was heated to 100 deg C. The resolution was impaired slightly (less than 3%). There was no detectable loss of counting efficiency. (L.T.W.)

The Preparation of Carrier-free 234Th(UX1) by Anion Exchange from Nitric Acid-Alcohol Mixed Solution of Uranyl Nitrate

The procedure for preparation of carrier-free Th/sup 234/using an anion exchanger Dowex 1 - X 8 was studied. The UO/sub 2/SO/sub 4/ was passed thru the column in HNO/sub 3/ Th was eluted by HNO/sub 3/ or water. An aliquot of the solution was transferred to a glass counting dish and evaporated to dryness. The alpha and beta activities were counted using a gas-flow proportional counter and G-M counter respectively. The Th/sub 234/ yield from l gm uranyl nitrate crystal was 4.6 x 10/sup 5/ dpm (Th/sup 234/ + Pa/sup 234/), and the radiochemical impurities were not observed by alpha and beta energy measurements. (L. N. N.)

A Low Background Beta Counter with a Plastic Scintillator Anticoincidence Shield

The design and performance of a low background beta counter is described. The counter consists of a central gas flow proportional counter surrounded by a large plastic scintillator anticoincidence shield.

247. Low background gas-flow counter: G. H. Bergold and G. R. Haney, J. Sci. Instrum.36, 39–44, Jan. 1959

A synchronized accumulating radioisotope detector for radio gas chromatography was developed. It comprised seven gas-flow proportional counters each with an inner volume of 10 ml. Every counter tube was connected by a mutual anti-coincidence circuit to reduce the background. The transit time of gas particles in one counter tube could be set to an optimal value between 1 and 4 s by regulating the flow-rate of the counting gas, according to analytical requirements. The improved detector maintained high chromatographic resolution, which suggested the applicability of the apparatus to capillary gas chromatography.

Determination of Calcium in Wolframite Concentrates by Fluorescent X-Ray Spectrography

AbstractThe purpose of this investigation was to develop a rapid, accurate method of analysis for small amounts of calcium in wolframite concentrates. This analysis is necessary to determine if wolframite concentrates meet the U. S. National Stockpile Specification P-57R2, which limits the calcium content to 0.2 per cent.Because of the small depth of sample analyzed in fluorescent x-ray spectrography the calcium Kα line intensity was found to be a function of the chemical composition of the calcium-bearing particle as well as the matrix composition. This particle-conn position effect was particularly important in this analysis because the calcium may be present as a carbonate, tungstate, phosphate, etc. Three methods of sample preparation were found to eliminate the variation of calcium Kα intensity with mineralogical occurrences: (1) Reduction in particle size by extensive grinding, (2) chemical fusion wtli sodium carbonate, and (3) solution of the calcium by an add.Determinations by all three procedures are believed to be accurate to within ± 5 per cent for more than 0.30 per cent calcium and ± 10 per cent at the 0.1-per cent level. The lower limit of detectability is in the order of 0.005-0.01 per cent.The operating characteristics of a gas-flow proportional counter used in conjunction with a pulse-height analyzer were studied in detail. This detector was found to have a high counting efficiency for calcium Ka radiation, to have a low counting efficiency for overlapping higher order radiation and to have counting stability equivalent to Geiger tubes.

The Adsorption of Tritiated Sodium Dodecyl Sulfate at the Solution Surface Measured with a Windowless, High Humidity Gas Flow Proportional Counter

The Adsorption of Tritiated Sodium Dodecyl Sulfate at the Solution Surface Measured with a Windowless, High Humidity Gas Flow Proportional Counter

Gas-Flow Proportional Counter for Soft X-Ray Detection

One of the major problems of analysis in the soft x-ray region is the limitation due to low transmission of the window materials of sealed-off x-ray detectors. This paper describes the properties and use of a gas-flow proportional counter system for the x-ray analysis of elements in the third period of the periodic table, with special reference to aluminum and silicon. The use of gases flowing continuously through the counter at atmospheric pressure in conjunction with helium also at atmospheric pressure in the optical path permits the use of ultra-thin nonvacuum-tight windows with high transmission in this region. Comparative data, obtained on a Norelco fluorescence spectrometer, show a tenfold increase in counting efficiency for AlKα over detectors previously available for this application.

A Precision Alpha-Proportional Counter

An instrument is described which will detect and record the alpha-disintegration rate of prepared radioactive samples even though soft beta-radiation up to 5×109 disintegrations per minute may also be present. The counting losses arising from the detector, electronic amplifier, scaler, and recorder total 0.8 percent with an alpha-counting rate of 105 counts per minute. The instrument employs a proportional counter through which 99 percent CH4 at one atmosphere slowly flows. The proportional counting region is approximately 300 volts in length, with 0.5 percent change in counting rate in an interval of 200 volts. Thin radioactive samples deposited on metal disks up to 2.5 cm in diameter are easily inserted into the counter volume by means of a special gas lock. The counter detects 0.50 of the disintegrations from a thin radioactive sample. The counter background can be maintained at about 14 counts per hour. A high vacuum, low geometry attachment provides reductions in geometry down to at least 10−5 of the sample counting rate. Some theory of gas-flow proportional counters is presented along with details of the instrument construction.