Gas-flow Proportional Counter Research Articles

Determination of241Pu by low level β-proportional counting. Application to Chernobyl fallout samples and comparison with the241Am build-up method

A chemical separation procedure is described which allows the direct determination of low241Pu activities in environmental samples with a windowless gas-flow proportional counter. While current separation schemes based on anion exchange yield counting sources of sufficient purity for subsequent α-spectrometry, for β-counting of241Pu additional purification steps are required. A combination of anion exchange from 9 mol/l HCl, LaF3 precipitation and TTA extraction was found to be suitable even for the analysis of long-range Chernobyl fallout samples which contained interfering radionuclides with β-activities at least 3 to 4 orders of magnitude higher than usually encountered. No difference is detectable between the results of the present, direct procedure and the results of the conventional indirect method based on the build-up of241Am. Average241Pu/239+240Pu ratios in air and deposition samples taken at Neuherberg near Munich were 70±6 with the present procedure and 66±9 from241Am build-up.

Optimization of a conversion electron Mössbauer spectroscopy gas flow He/CH4 proportional counter

A new detector for CEMS has been built and optimized with respect to the statistical quality of spectra obtained. The optimization has been performed by measuring Mosbauer and pulse height spectra at in- and off-resonance. Single channel analyzer settings were calculated by a new optimization routine. A comparison of different detector designs has been performed using the statistical utility rate of spectra obtained from a stainless steel foil. A procedure for determining optimal operating parameters for ICEMS gas flow proportional counters is proposed.

Determination of 89Sr and 90Sr radioactive concentrations from least-squares fits to the growth/decay curves

A method has been developed for determining the radioactive concentration of 89Sr and 90Sr in samples, using the 90Y growth curve and the 89Sr and 90Sr decay curves. Experimental data are obtained by successive counts of the sample activity as measured by a gas-flow proportional counter. Least squares fits are then made to the theoretical curves. A discussion is given of the number of measurements needed and the most suitable dates for making them relative to the radiochemical separation date of the strontium.

The half-life of 237Np

The only available precise measurement of the half-life of 237Np is that of Brauer et al. (J. Inorg. Nucl. Chem. 12 (1960) 234), which dates from 1960. As a consequence of this radionuclide's importance in fission reactors, the IAEA-CRP requested a confirmatory measurement of the half-life of 237Np.In this present determination the specific activity of 37 sources, prepared from known masses of high purity 237Np solution, have been measured. Accurate concentration analysis of the solution was provided by controlled-potential coulometry. Source activities, in the range 1.0–1.9 kBq. were measured by α-particle counting in two gas flow proportional counters of known geometry.The measured specific activity was 26.03±0.08 Bq μg−1, which corresponds to a half-life of 2.144±0.007 × 106 years, in excellent agreement with the value reported by Brauer et al.

The use of avalanche photodiodes for the detection of soft x rays

Avalanche photodiodes (APDs) offer an attractive alternative to the gas flow proportional counter (GFPC) for the counting of individual soft x-ray photons. They are reasonably efficient detectors and have the capability of handling higher count rates than a GFPC. With the advent of intense monochromatic x-ray beams from synchrotron radiation sources, the ability to handle high count rates is becoming more important than the need for any energy resolution. Another attraction of using solid-state detectors is the possibility of multielement fabrication of devices: configured detector arrays can then be considered for a number of applications. For example, in the scanning transmission x-ray microscope such a detector system allows much more sophisticated imaging techniques, such as differential phase contrast imaging with a quadrant APD array. In this paper we compare results for several commercially available APDs used as photon counters with a GFPC over the energy range 200–700 eV. APDs operated in the Geiger mode with a simple passive circuit to quench the avalanche current pulses can achieve count rates of the order of 106 s−1, and this can be greatly improved upon with the use of an active quenching circuit.

Depth-selective 57Fe CEMS (DCEMS) on samples with rough surfaces using a gas flow proportional counter

Abstract The possibility of semi-quantitative depth-selective analysis of surface layers of specimens unenriched by 57Fe by means of a gas flow proportional counter is demonstrated. The optimal energy intervals for electron detection and corresponding depth-integral weight functions were determined. The influence of surface roughness on the surface selectivity of DCEMS as well as for conventional CEMS was experimentally studied. The dependence of depth selectivity on certain parameters of the detection system was investigated in detail.

New possibilities of the x-ray standing wave method in multiple diffraction of synchrotron radiation

Results of measurements of the reflected beam intensity and photoelectron yield under conditions of dynamical 111/220 diffraction of synchrotron x-ray radiation are presented. The experiments were carried out on beam lines 15C and 14B at the Photon Factory. Two possible multicrystal arrangements were used for the preprocessing of the incident beam. In the first one, a double-crystal Si (111) monochromator was used for monochromation and collimation of the x-ray beam in the vertical plane and a Si (220) channel-cut crystal was used for collimation in the horizontal plane. The second crystal arrangement is based on a (111)-oriented Si crystal adjusted for a six-beam Laue diffraction condition. The anomalously transmitted (μt/γ0 ≊ 40) beam was used as an incident beam in the x-ray standing wave measurements. The angular dependence of the total photoelectron yield was measured using a gas flow proportional counter.

Determination of the co-monomer content in tetrafluoroethylene/perfluoro(propylvinyl ether) copolymers by XRF analysis.

A quantitative analysis of an oxygen-containing co-monomer in organic copolymers by an XRF oxygen analysis was investigated. An X-ray fluorescence spectrometer was equipped with a diffraction device having synthetic multilayers (2d=8.06 nm) and a gasflow proportional counter as a detector for the O Kα line with a 0.6 μm polyester film window. The X-ray tube was used with a large current under low potential (40 kV-70 mA); the intensities of the O Kα peak (2θ=34.325°) and those of the background (2θ=33.00, 36.03°) were measured three times for 100 s and 3 times for 50 s, respectively. A calibration curve was constructed based on the oxygen contents of tetrafluoroethylene/perfluoro(propylvinyl ether) copolymer, determined by the IR method. It showed good linearity over an oxygen content range of 0.12% (110 mol % as co-monomer); the relative standard deviation was 2.7% for seven measurements of a 1.12 % oxygen-containing polymer. A rapid, nondestructive determination method of an oxygen-containing co-monomer by XRF was thus established.

Quantum efficiency of a semiconductor photodiode in the VUV determined by comparison with a proportional counter in monochromatized synchrotron radiation

A procedure based on a gas flow proportional counter and the possibility of achieving well-known flux ratios with the BESSY electron storage ring is used to determine the quantum efficiency of a semiconductor photodiode.

Half-lives of 44Ti and 207Bi.

An end-window gas-flow proportional counter system, including an automatic precision sample changer, was used to measure the decay of radiations from two samples of {sup 44}Ti and one of {sup 207}Bi. Comparison counts were taken on a {sup 36}Cl standard, and the ratio of counts determined the decay. Points consisted of alternate 30-min counts on each sample and on the standard, totaling 30 h on each, and were taken at intervals of about one month. Based on 3 years of counting on the {sup 207}Bi source and on one of the {sup 44}Ti sources, and 1 year on the second {sup 44}Ti sample, half-lives were obtained as follows: {sup 44}Ti, 66.6(16) yr and {sup 207}Bi, 34.9(4) yr. The {sup 207}Bi value lies between the two most recently reported values. In the case of {sup 44}Ti there are discrepancies with all three previous results including an Argonne accelerator mass spectroscopy value of 54.2(21) yr.

A set of X-ray fluorescence reference sources for the intrinsic efficiency calibration of Si(Li) detectors down to 1 keV

X-ray fluorescence sources were prepared and their emission rates certified with an accuracy of better than 2%. The sources were standardized using a gas-flow proportional counter in a defined low-solid-angle setup. They were used for the efficiency calibration of a Si(Li) detector at the characteristic K X-ray energies of Al, P, S, Cl, Ca and Ti.

Efficiency calibration of Si(Li) detectors with X-ray reference sources at energies between 1 and 5 keV

Fluorescence sources were prepared and their KX-ray-emission rates certified with an accuracy of better than 2% using a gas-flow proportional counter in a defined low-solid-angle setup. These sources were used for the efficiency calibration of a Si(Li) detector at the characteristic KX-ray energies of Al, Cl, Ca and Ti.

Determination of phosphorus in biological samples by thermal neutron activation followed by β--counting

Phosphorus has been determined using the β- emitter32P by instrumental neutron activation analysis (INAA) in several NBS and IAEA standards and samples of biological origin such as human and animal blood, cancerous tissue, edible plant leaves, diets, milk samples, etc. The method involves thermal neutron irradiation for 2–10 h in a reactor followed by β--counting on an end-window gas flow proportional counter using an aluminium filter. The results are within ±10% of the certified values in most cases.

A coincidence system for radionuclide standardization using surface barrier detectors

A system for the standardization of alpha-gamma or electron-X radionuclide emitters is described. The system consists of one or two surface barrier detectors for alpha or electron detection which are coupled to thin-window NaI(Tl) crystals suitable for low-energy X- or gamma-ray detection. The performance of the system has been verified by the standardization of 241Am, 137Cs and 109Cd solutions. The activity has been obtained using the extrapolation method applied to the 4π α-γ and 2π e-X coincidence techniques. The surface barrier detection efficiency was varied by placing absorbers over the radioactive source or by changing the source-to-detector distance. The results were compared to those obtained using conventional absolute systems based on gas-flow and pressurized 4π proportional counters, or using radioactive solutions standardized in international comparisons sponsored by the Bureau International des Poids et Mesures, France. The expected and measured activities agreed within the experimental uncertainties, which were: 0.2% for 241Am, 0.7% for 137Cs and 0.6% for 109Cd.

Beamline and irradiation chamber for dosimetry and biology studies using synchrotron radiation

Ultrasoft x rays are a useful probe for mechanistic studies of radiation damage in living cells. The highly localized energy deposition from a low energy x-ray occurs in a volume comparable to the sensitive biological targets within a cell, so that these low-energy x rays can be used as a tool to investigate radiation effects on the subcellular level. In the ultrasoft x-ray energy region the bright intensity and tunable energy selection of synchrotron radiation is unmatched by conventional sources. A beamline and irradiation chamber for dosimetry and radiation biology studies has been set up at the ES-0 exposure station of the Center for X-ray Lithography at Aladdin. The beamline includes a 10-μm-thick Be entrance window and a combination filter and single synthetically fabricated multilayer mirror for energy selection. The irradiation chamber contains another Mylar window for isolation, a two-dimensional scanning system allowing a 400-cm2 exposure area with scanning rates up to 3.5 cm/s, a rotating feedthrough system that enables motion in the third dimension, several viewports and a specially designed cell sample holder which can be filled with gases at various pressures and holds up to 18 cell culture dishes. The system has been characterized with a gas flow proportional counter to determine energy bandpass and spectral purity and a calorimeter and ionization chamber to assess photon intensity at various energies within the range 500–2000 eV.

Compact fluorescence x-ray detector for surface EXAFS and x-ray standing wave measurements

The design and performance of a compact, ultrahigh vacuum (UHV) compatible x-ray detector is described which can be applied to measurements of surface EXAFS spectra and x-ray standing wave (SW) profiles. The detector is a type of gas flow proportional counter. Its compactness allows us to save space around the sample. A 25-μm-thick beryllium window separates UHV (<1×10−10 mbar) environment from atmospheric pressure and provides good efficiency to detect low energy x rays. Surface EXAFS spectra of less than 0.1 monolayer chlorine on a Ni substrate are successfully measured with high quality. Its high signal-to-background ratio allows us to measure SW profiles, which could hardly be obtained with any electron yield detection technique.

Counting equipment “dead time” independent of net count rate of a radioisotope

It has been published that the “dead time” of a G—M counter depends on the measured count rate. In this paper it is shown that the “dead time” is a constant over a limited range from zero to an observed net rate R n . From the fundamental equation τ′, R i R o i o = 1 − τ′R i , we get R i↑q i = ( R q ) o− [τ′( R q ) o]R i , where i = 1 to n, R i and R i o are the observed and true net count rates, q i is a measured physical quantity proportional to the absolute disintegration rate of any radioisotope source S i, ( R q ) o = R i o q i is the true net rate per unit quantity and R i o = q i( R q ) o . The ratio τ′ ∗ = [τ′( R q ) o] ( R q ) o is called the rational overall resolving time per count for a particular counting equipment instead of the “dead time”. At higher net rates R k (> R n ⩾ R i > 0) the parameters, A Δ and B Δ , of R k ↑ q k = B Δ − A Δ R k may be evaluated for various rate intervals ΔR k of the nonlinear ( j = k > n) portion of R j q j vs R j . The values of A Δ B Δ in R k↑q k B Δ = 1 − ( A Δ B Δ )R k have no physical meaning and A Δ B Δ is called the pseudo-resolving time per count. It was found that A Δ B Δ depends on R k lying in various ΔR k rate intervals, R k q k B Δ ≷ 1 − τ′ ∗ R k and ( R q ) o ≷ B Δ . Hence R k q k B Δ ≷ R k R k o , where R k o = q k( R q ) o for any source S k with k = n + 1, n + 2, etc. Raw count-rate data taken from three publications have been used for a comparison of τ′ ∗ with values of A Δ B Δ in the case of G—M, NaI(Tl) scintillation and gas-flow proportional counters.

Improved synchronized accumulating radioisotope detector for gas chromatography

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.

Proportional counter for low-level 241Pu measurement

A windowless gas-flow proportional counter for the measurement of 241Pu electrodeposited on stainless steel discs is described. The lower limit of detection is found to be 5 mBq at 60000 s counting time.

Mass attenuation coefficients of beta particles in 4π geometry

The mass attenuation coefficients μ/ϱ of beta particles of end point energy E 0 ranging from 0.16–2.3 MeV are determined adopting a 4π geometrical configuration, where the source is sandwiched between thin foils of aluminium as absorbers and the sandwich is kept in a 4π gas flow proportional counter for measuring transmitted beta particles. An empirical relation connecting μ/ϱ and E 0 is determined in such a geometrical configuration for the first time. The estimated values of μ/ϱ in this geometry are discussed and compared with published values, obtained by employing various other types of geometry.