Cylindrical Proportional Counter Research Articles

Designer and properties of a multianode, cylindrical proportional counter for position sensing at high count rates.

A cylindrical proportional counter with six anode wires was designed and tested. The electron drift velocity was greater than that of similar single-anode, coaxial proportional counter, thus, allowing counting and position sensing of low-energy photons (<60 keV) at high count rates (≳105 counts/s).

Further studies of cylindrical proportional counters for microdosimetric work

Walled and wall-less tissue-equivalent cylindrical proportional counters of unit elongation have been constructed and their performance extensively studied and compared with that expected from the theory of conventional proportional counter. The difference in behaviour between the walled and wall-less counters as regards energy resolution, gas gain, sensitive volume etc., is attributed to the wide grid structure of the latter. The transit time of single electrons released from the cathode walls by UV light has been measured in tissue-equivalent gas as a function of E/ p for working pressures of 81, 57, 30 and 20 torr.

Optimization of the energy resolution of methane filled cylindrical proportional counters

The energy resolution of proportional counters depends on the axial and the statistical fluctuations of the gas multiplication factor. It is shown how these fluctuations can be minimized by an appropriate choice of the counter dimensions.

Empirical expressions for gas multiplication in 3He proportional counters

The inter-dependence of the operating parameters of cylindrical proportional counters has been investigated. A detailed description of previous work is presented, including the development and verification of several empirical formulae. Experimental data from 18 counters were used to develop four improved expressions, one of which can be used to predict gas multiplication to an accuracy of better than 98%.

A high-resolution cylindrical proportional counter for neutron-spectrum measurements in a fast critical assembly

Compact proportional counters filled with hydrogen and with methane, respectively, have been constructed for measurements of fast-neutron spectra in a fast critical assembly. Field tubes made by metallizing a ceramic-seal surface are satisfactory to remove recoil events in the volume defined by the tubes. The best resolution of the hydrogen-filled counter is 3.8% at a gas multiplication 17.6. The total number of electrons collected before saturation in gas multiplication occurs is about 2 × 10 5 when initial ionizations are highly localized or the direction of a recoil-proton track is nearly perpendicular to the anode wire. A value of 14 MeV is recommended to the product of energy loss and gas multiplication as a critical value for the proportional mode of operation. This value is about one seventh as large as the values reported previously.

Counting rate dependent gain shifts in flow proportional counters

The counting rate dependent shift of pulse height distributions in cylindrical (flow) proportional counters has been studied. The effects of various counter tube constructional and operational parameters on this shift were investigated. Certain of these parameters also introduce time dependent features into the shift phenomenon. Space charge effects are not major causes of the shifts except under extreme operating conditions. Direct intervention of adsorbed molecules or molecular ions in the multiplication process may also be eliminated as major factors. It is hypothesized that the primary mechanism for the shift is the buildup on the anode wire of a loosely adherent sheath of polarizable molecules or molecular fragments of quench gas, which effectively increases the diameter of the anode wire, thereby decreasing the gas gain for a fixed applied voltage. The equilibrium thickness of the sheath is a function of counting rate, photon energy, gas gain, gas pressure, and wire diameter and surface condition. Calculation of the thickness of this sheath gives a reasonable result. By proper choice of anode wire diameter, material, and heat treatment, the shift can be made negligible. There is also some hope that a proper choice of quench gas can also reduce or eliminate the effect.

Multiwire counting

The application of multiwire counters instead of the corresponding cylindrical proportional counter in low-level gas counting, electron-capture studies and fluorescence-yield determinations is discussed. By studying the spectrometric properties of the ring counter the possible deterioration of the energy resolution due to a deviation of the electric field around the counting wires from axial symmetry was estimated as negligible.

Neutron spectrometry with proton-recoil proportional counters in the energy region up to 10 MeV

Large cylindrical proportional counters have been used in parallel neutron beams for spectrum measurements in the energy region up to 10 MeV. Measurements with monoenergetic neutrons and a series of comparisons with other techniques showed that results with similar accuracies, as are claimed in the low energy region (2 MeV), can be obtained. Problems specially related to the high energy region are discussed.

Statistics of electron avalanches and ultimate resolution of proportional counters

This paper deals with the fundamental limitations set on the ultimate energy resolving power of a proportional counter. An analysis of a few statistical models of electron avalanches in gases subjected to uniform electric fields is performed. A formula for gas amplification variance in non-uniform fields is derived. The relative variance of gas amplification in argon and methane filled cylindrical proportional counters for the case of K = 10 2–10 5 and pr a = 1–4 torr·cm is calculated to be 0.6 to 0.8. The present work shows that avalanche size distributions in uniform fields are close to those computed by Legler, but that the distributions in the non-uniform fields of cylindrical counters are close to those of Polya-type.

The Determination of LET Spectra from Energy-proportional Pulse-height Measurements II. A Monte Carlo Unfolding Procedure

The mathematical problem of unfolding LET spectra from observed pulse-height measurements is formulated and analytic solutions for the sphere and infinite slab are discussed. An iterative Monte Carlo procedure is presented for unfolding LET spectra from pulse-height measurements from any energy-proportional device. The method, which utilizes track-length distributions obtained by the technique described in the preceding paper, Part I, places no restrictions on the geometrical shape of the device or on the geometry of the source of particles bombarding it. The procedure is applied to examples of charged-particle and neutron irradiation in which both spherical and cylindrical proportional counters are considered. While no exhaustive study is attempted, the results show that, even in its simplest form, the method could be adapted to routine health physics monitoring. Ways of improving the procedure and incorporating more elaborate programs are discussed.

National Taiwan University Radiocarbon Measurements I

Natural C14 measurements have been performed at the Dept. of Physics, National Taiwan University since 1965, using a cylindrical proportional counter of 1000 ml (Hsu et al., 1965). The proportional counter is operated with CO2 as the filling gas at a pressure of 1216 mm Hg at room temperature of 20°C. Working voltage is 4.7 Kv, with a plateau length of more than 700 v and a plateau slope of ca. 1% per 100 v. Background is reduced to 5.1 counts/min and the counting rate of the NBS oxalic acid standard is 9.4 counts/min at the normal counting pressure of 1216 mm Hg.

Measurement of characteristics of cylindrical proportional internal-filling counters near the end insulators

We measured the counting characteristics of a cylindrical proportional internal-filling counter in the region of field distortions caused by the end insulator. The reduction of the counter's recording efficiency near the end insulator, caused by distortions of the electric field, was measured experimentally.

Choosing the operating point on the count rate characteristic of a cylindrical proportional counter

1. A criterion for choosing the operating point on the count rate characteristic of a cylindrical proportional counter of the “expandable chamber” type has been proposed. 2. It has been shown the operating point is located at the end of the plateau on the count rate characteristic. 3. It has also been shown that the counter, whose central needle electrode is divided into two parts by an insulating bead, can be used for various measurements as a chamber of adjustable volume.

Calculation of the detection efficiency of a cylindrical counter for X-rays from an internal source

This paper describes detailed calculations of the efficiency of a long cylindrical proportional counter for detection of X-rays from an isotropic point source placed centrally in the wall of the counter. The results are applicable to counters of varied length and radius for a range of X-ray energies and are presented in both analytic and graphical forms.

On electron drift velocities in mixtures of noble gases and “moderator” gases

Theoretical investigation of electron drift velocities in noble gas-“moderator” gas mixtures under the influence of an electric field has yielded a new scaling law w= E p G(z) 1+αH(Z) where G and H are functions of the parameter z = α/( E/ p) 2 only. Here, w is the electron drift velocity, E the electric field strength, p the gas pressure and α the concentration of moderator gas. The conditions limiting the validity of this scaling law are discussed. Comparison of the law to existing experimental data (Ne, A, Kr, Xe with CO 2; A, Kr with CH 4) demonstrate the validity over a wide range. The functions G and H derived from these data are presented. The existing drift velocity data, having been condensed to this more manageable form, is applied to the computation of electron transit times in cylindrical proportional counters using any of these gas mixtures.

Low level proportional counter for tritium

A proportional counter for the measurement of low tritium activities is described. The cylindrical proportional counter (principal counter) with a volume of about 600 cm 3 is the inner part of a low level counting system in which the guard counter (anti-coincidence counter) surrounds the principal counter which is only separated from the annular counter by a thin foil. The ratio of the “transmit” to the “out” counting rate is high compared to other low level counting systems (of the order of 300). The specific feature of the design is the separation of the volume of the internal counter and the anti-coincidence counting ring. The special properties of the counter and some of its operations are discussed.

Parameters affecting the resolution of a proportional counter

This paper describes measurements of the dependence of the gas gain of a cylindrical proportional counter on the anode and cathode radii, anode voltage and the gas density. From these measurements, the effect on the resolution of variations in these parameters is calculated. A theoretical formula for the gas gain is derived which gives good agreement with the experimental results.

Large Proportional Counter Spectrometer for the Study of Radioactive Samples with Low Specific Activity

The design and construction of a cylindrical proportional counter 36 in. long, 12 in. i.d. is described, and its performance as a spectrometer for studying soft radiations from radioactive samples of low specific activity is given. The counter tank is operated in an axial magnetic field of 2500 gauss to constrain beta rays to helical paths. A line width of 3.4% (ΔE/E) is obtained for 625-kev electrons from a Cs137 source mounted on a thin film placed within the tank. Simple theory would predict 2.2%. Beta spectra are readily obtained with sources having total activities less than 10 mμC.