High Counting Efficiency Research Articles

A Position-Sensitive Proportinal Counter for Residual Stress Measurement by means of Microbeam X-Rays

AbstractA position-sensitive proportional counter (PSPC) with high counting efficiency has been made for stress analysis with low intensity X-rays such as microbeam X-rays.This PSPC system has made it possible to measure the residual stress in a small region such as a fatigue crack tip in very short time compared with the measurement by standard diffractometer or film methods.

Čerenkov counting and Čerenkov-scintillation counting with high refractive index organic liquids using a liquid scintillation counter

Fluorine-18 and carbon-14 radioactivity was measured in methyl salicylate (MS), a high refractive index hybrid Čerenkov-scintillation generating medium, using a liquid scintillation counter. At concentrations of up to 21.4%, in MS, dimethyl sulfoxide (DMSO) quenched 14C flourescence, and with a 10-fold excess of DMSO over MS, 18F count rates were reduced below that for DMSO alone, probably as a result of concentration-independent self-quenching due to “dark-complex” formation. DMSO in lower concentrations did not reduce the counting efficiency of 18F in MS. Nitrobenzene was a concentration-dependent quencher for both 14C and 18F in MS. Chlorobenzene (CB) and DMSO were both found to be weak Čerenkov generators with 18F. Counting efficiencies for 18F in MS, CB, and DMSO were 50.3, 7.8 and 4.3% respectively in the coincidence counting mode, and 58.1, 13.0 and 6.8% in the singles mode. 14C efficiencies were 14.4 and 22.3% for coincidence and singles respectively, and 15.3 and 42.0% using a modern counter designed for coincidence and single photon counting. The high 14C and 18F counting efficiency in MS are discussed with respect to excitation mechanism, on the basis of quench and channels ratios changes observed. It is proposed that MS functions as an efficient Čerenkov-scintillation generator for high-energy beta emitters such as 18F, and as a low-efficiency scintillator for weak beta emitting radionuclides such as 14C.

High Purity CdTe and Its Application to Radiation Detectors

High quality CdTe single crystals with room-temperature resistivity of 106Ω·cm have been grown from Te solution by a travelling heater method. The optimum growth conditions are settled to be growth rate of 3 mm/day and growth temperature of around 65°C. A possibility to get much higher resistivity by controlling the Cd vapor pressure over the Te solution is suggested. A preliminary experiment of radiation detectors using 106·Ω·cm crystals has been performed. Although the experimental results are not satisfactory at present, a high counting efficiency for γ-ray superior to Ge detectors is confirmed; suggesting promising applications to environmental monitors for selfguard systems and nuclear probes for nuclear medicine.

Continuous Monitoring of Radioactivity of Effluent from a High-Speed Amino Acid Analyzer, with a New System of Sample Segmentation

Radioactivity in the effluents from high-speed liquid chromatographic analyzers was continuously measured by use of a new sample segmentation system. To achieve highest counting efficiency, the column effluents were mixed with scintillation fluid carrying small segments of semisolid, resillient spacer. After passing through a mixer, the mixture was passed through a hollow-tube flow cell mounted in a liquid scintillation spectrometer. Because the added spacer acts like a continuous series of pistons, it unifies flow rate at center and walls of the conduit and so decreases sample carryover. This system was applied to measurement of radioactivity in the effluent of a high-speed amino acid analyzer, in which some amino acids emerge at 30-s intervals. The resulting profiles were as well resolved as were the ninhydrin-color profiles. Counting efficiencies for tritium and carbon- 14 were comparable to those obtained by static counting in vials.

A new cocktail for liquid scintillation counting of aqueous radioimmunoassay-samples

The aim of this investigation was to find a scintillation mixture for counting up to 1 ml of plasma. We succeeded in obtaining a mixture of xylene/Triton X-100/mono- and di-butylphosphate, and called it Plasmasol. The properties were ideal for radioimmunoassays of steroids. Good dissolving properties, high counting efficiency, absence of chemiluminescence and a good stability and reproducibility with respect to the disintegrations per minute were achieved. The cost was only 25% of the commercially available ready-to-use liquid scintillation mixtures, with which a comparison was made.

Multichannel Miniature Semiconductor Detector System with On-Line Computer Analysis for Measurement of Miniregional Cerebral Blood Flow

This paper outlines our experience over the past decade, with a multichannel miniature semiconductor detector system for measurement of miniregional cerebral blood flow. 8 channels of a lithium drifted silicon detector system with on-line computer analysis are satisfactorily operating in monitoring quantitative regional cerebral blood flow on multisites of the brain in vivo in humans as well as animals. More recently, our experience with a highly gamma sensitive Cadmium Telluride detector (CdTe) was disappointing. For 133Xe clearance studies, the CdTe detector gave a 5 times higher counting efficiency than the Si(Li) detector. However, blood flow values obtained by Stochastic analysis from the CdTe detector are 25 to 40% less than the values obtained from the Si(Li) detector. This problem appears to be mainly due to a trapping phenomenon occurring in the CdTe detector which gives a non-linear response between radioactivity and count rate, and over exceeds random fluctuation of count rate. These genetic and temperamental features of the CdTe detector make it unsuitable for use in measurement of cerebral blood flow at the present time. Our clinical and laboratory experience with miniature semiconductor systems will be reviewed.

Application of the radiotracer method for the study of electrosorption of carbon dioxide on platinum

An apparatus for the study of carbon dioxide adsorption (labelled with 14C) on platinum electrodes from 0.5 M H 2SO 4 solution has been developed. The working electrode was prepared by the electroplating of gold, deposited onto a mylar foil. A plastic scintillator was placed under the electrode to achieve a high counting efficiency (∼ 15 per cent). Owing to the construction of the apparatus the study of adsorption dependence on temperature was made possible. It has been shown that the CO 2 adsorption on platinum (in the potential range 0–0·35 eV) is a result of interaction with H ads. The surface concentration of “reduced CO 2” on platinum, and the charge needed for its oxidation reveal that the adsorbed species is a COOH radical.

Thin 4 π sources on electrosprayed ion exchange resin for radioactivity standardization

Anionic and cationic ion exchange resins are prepared as suspensions in ethanol of finely ground particles (<0·3 μm) and electrosprayed simultaneously onto metallized VYNS substrates. The reins are deposited to form circular pads in the range from about 1·5 μm cm -2 upwards and 6–20 mm in diameter to provide sufficient capacity for absorbing all non-volatile ionic material in the source drop. The pads have satisfactory electrical conductivity and high physical stability, and the ions are readily diffused uniformly throughout their structure. These characteristics lead to sources with high counting efficiencies, up to 0·985 for 60Co, and high reproducibilities of counting efficiencies. For 35S and 63Ni the reproducibilities can be within ±0·2 per cent. By diffusing suitable pairs of radionuclides into the same resin pad one can make uniformly and homogeneously distributed sources for efficiency tracer measurements; counting efficiencies can be decreased in arbitrarily small steps by electospraying additional resin over the source. Brief references are made to other proven applications of thin resin layers which are potentially important in the fields of radioactivity standardization and chemical analysis.

An evaluation of liquid scintillation counting techniques for use in aquatic primary production studies1

Methods evaluated for the liquid scintillation counting of samples from aquatic primary production studies include the counting of intact filters and cells in a toluene fluor, solubilization and counting of membrane filters and cells in various reagents, and counting of a suspension of cells mixed with the fluor. A 1:1 Triton X‐100:toluene fluor was very effective for the suspension of cells and gave high counting efficiencies. Up to 5 ml of sample could be mixed with the fluor, but this was considered inadequate for most primary production studies.The filter standardization method for the counting of intact filters was investigated further and found to be applicable over a wide range of conditions but only accurate when the weight of algae on the filters was small (&lt; 1 mg).Direct solubilization of the filters and cells in a naphthalene‐dioxane or 2‐methoxyethanoltoluene fluor were the simplest, most accurate, and economical methods for primary production studies; the latter dissolved both wet and dry cellulose nitrate membrane filters and gave excellent replicate counting.

An improved scintillation probe for continuous counting of expiratory 14CO 2-gas

The combination of an expiratory CO 2 flow system and a scintillation counting system is described for the continuous counting of respiratory 14CO 2 exhaled from a mouse. Respiratory H 2O is trapped by a cooling trap to eliminate quenching effects of water on the counting. Dried air with expiratory 14CO 2-gas is fed to a given volume of the hyamine scintillation fluid in the reservoir and is bubbled in the fluid to trap 14CO 2-gas. A portion of the radioactive scintillation fluid is fed into a scintillation probe and returned to the reservoir continuously by connecting the reservoir and the probe with fine teflon tube. In the probe, the tube is coiled and placed between opposing photomultiplier tubes. The probe is connected with 2 ratemeters following a recorder for continuous counting of radioactivity in the flow stream. This device is particularly suited for the continuous counting of expiratory 14CO 2 with high counting efficiency as well as that of a liquid scintillation counter. The expiratory 14CO 2 patterns did not vary with the date, if the same mouse was used during 10.00 a.m. – 1.00 p.m. The patterns of different mice also were almost concordant. Discussions are described in detail for the comparison of respiratory 14CO 2 patterns given by this device and the other counters.

Detailed description of a simplified radio-liquid chromatograph

The details of a simplified radio-liquid chromatographic system for simultaneous recording of light absorbance and radioactivity of the eluate from liquid or gas chromatographic columns are described. The counting efficiency of the radiation detection system was dependent upon the relative flow-rates of the eluate and the scintillation mixture. A high counting efficiency was obtained with naphthalene in a dioxane type scintillation fluid. No change in efficiency was noted when nebulization and cavitation for more complete emulsification were omitted from the system. Overall counting efficiencies for the systems were 45.5% for tritiated materials and 82.7% for 14C labelled materials. An interval of about 30s was required to obtain resolution between different patterns of radioactivity. The minimum volume of radioactive material needed for monitoring was 0.01 ml of 0.06 μCi per ml for tritiated materials. By simultaneous recording of light absorbance and radioactivity of different pyrimidine ribosides, 14C-cytidine and and 3H-uridine, good discrimination of beta energies were obtained and the counting efficiency was similar to that of a liquid scintillation counter.

A new approach to the radiometric study of methanol adsorption on platinum

Summary A new apparatus for the study of electrosorption of organic species labelled with 14 C has been developed. A platinum working electrode was prepared by the electroplating of gold deposited on mylar foil. A plastic scintillator was placed immediately under the electrode to achieve a high counting efficiency. The dependence of surface concentration of methanol on electrode potential has been investigated. The surface concentration increased with decrease in the electrode potential over the range 0.1–0.4 V. At potentials above 0.6 V a sharp fall-off in the surface concentration was found. The time required to reach steady-state coverage depends on electrode potential and on methanol concentration in the bulk of the solution. Some conclusions concerning the possible mechanism of methanol electrosorption are presented.

Methods for fractionation and scintillation counting of radioisotope-labeled polyacrylamide gels

This paper describes two polyacrylamide gel fractionators. One can be easily constructed from disposable syringes and used for fractionating standard-size analytical gels. The second is more complex but can be used for fractionating miniature gels. A rapid method of preparing gel fractions for liquid-scintillation counting is also presented. The method gives high counting efficiency, does not require hydrolysis of the gel prior to counting, and allows gel fractions to be collected directly in scintillation vials.

A high resolution Cherenkov chamber

A focusing type of Cherenkoc chamber is described, in which an image intensifier is used to record the ring images. A test experiment with 16 GeV/ c pions at the CERN proton synchrotron has demonstrated that the velocity resolution is δβ = 6 × 10 −7 for single pions. The precision in determining the mean velocity of the particle beam is limited by a systematic error δβ = ± 2 × 10 −7. From the results of this experiment, it can be concluded that a similar chamber should distinguish protons and kaons of equal momentum up to 200 GeV, with high counting efficiency and an angular acceptance of 5 mrad.

Radiometrische und Analytische Ausnützung der Natürlichen Instabilität von87Rb

Possibilities of radiometric determination of Rb in liquid and solid samples using87Rb are discussed. In spite of the relatively low β-ray energy of87Rb, it is possible to achieve relatively high total counting efficiency (up to 75%) using gas flow GM counters. This fact makes possible to use the natural instability of87Rb also for the purposes of calibration. In this paper the conditions of radiometric determination mainly of small amounts of Rb are described (minimum measurable amount is 0.07% of Rb).87Rb can be used for the minimum activity determination by measuring β-radiation in the interval of energy of 0.27 MeV.

Investigation of tissue extraction and liquid scintillation counting of tritium in dried whole tissue

This study investigates the solubility of dried whole tissue with several strong ammonia bases and liquid scintillation counting of tritium in base counting systems. Complete digestion and low colour quenching were obtained with Hyamin, NCS and Digestin by warming in air-tight vials. The scintillators BBOT, Butyl-PBD, BIBUQ and PPO+Dimethyl-POPOP in toluence solution were examined as to flourescence, self-quenching, optimal concentration and tolerance of bases. A remarkable influence of pH on countine efficiency was observed. The bases led to progressive colouring and to shifting of the flourescence spectra of the scintillators. Treatment by strong acids was followed by high counting efficiencies and stable counting rates. An external standard was used with good results for the determination of efficiency in routine counting.

Applying exoelectronic emission to the investigation of surface damages cause by radiation

The principles for applying the exoelectronic emission to the investigation of the surface damages caused by radiation are given. An improved method is described, which provides a high counting efficiency. The extinction of the emission ( T = 300°K) for γ-Al 2O 3 has been followed at various doses and dose rates of radiation. A rough value (≈0·2eV) is given for the activation energy of the exoelectrons at room temperature. The curves of the thermostimulated exoelectronic emission (TSEE) at various doses and dose rates of radiation are given which characterize the influence of the population of the various local levels (defects) on the emission properties of crystals. It is shown that the number of the emitted electrons rises by increasing the radiation dose; at the same time the deeper traps in the forbidden zone are filled. The kinetics of the extinction of the exoelectric emission for γ-Al 2O 3 vs. the number of chemisorbed atoms of hydrogen shows an increase during the chemisorption of the total number of centres which are capable of emission and have the character of donors, and at the same time the energetic distribution of the traps changes. It has been shown that the adsorption causes the appearance of a new distinct maximum on the TSEE curve; the height of this maximum depends on the quantity of hydrogen adsorbed. This shows that new emission centres have appeared. The position of the maximum determines the depth of the admixture level formed by the chemisorbed atoms in the forbidden zone. The influence of the isotope effect on the course of the thermostimulated emission before and after the adsorption of hydrogen and deuterium has been investigated. The first maximum on the curve of γ-Al 2O 3 + deuterium is shifted in comparison with the maximum on the curve of γ-Al 2O 3+hydrogen. It is supposed that electron traps in the surface formed under the influence of the adsorption of deuterium are situated on deeper energy levels than those formed during the adsorption of hydrogen.

Liquid scintillation counting techniques for the radioassay of [14C] melanin

AbstractThe radioactive melanin used in this study was extracted from the cell walls of the fungus Aspergillus nidulans after growth in the presence of 14C‐labelled precursors. The counting systems investigated comprised solid samples suspended in a liquid scintillator with or without silica gel, solubilized samples blended in a liquid scintillator and solubilized samples adsorbed on to glass‐fibre discs wich were suspended in a liquid scintillator. Results obtained by counting solid samples with an end window detector are compared with the liquid scintillation data. High counting efficiencies were realized with the glass‐fibre disc method which is recommended for the assay of soluble samples. Liquid scintillation counting of silica gel suspensions was vastly superior to end window counting for the assay of solid samples. The data suggest that 14C‐labelled materials of a particulate or highly pigmented nature can be counted with high efficiency in a liquid scintillation system.

Collection of C 14O 2 for scintillation counting by a modification of the Van Slyke procedure

A method for the collection of CO 2 for scintillation counting is described in which a simple absorption unit is used as an accessory to the Van Slyke-Neill blood gas apparatus. Carbon dioxide is absorbed directly in the scintillation vial immediately after the determination of the total CO 2 content of the samples. The procedure was tested for varying sizes of samples and absorbents. Phenethylamine is superior to Hyamine as shown by statistical analyses of the data and the higher counting efficiency. The technique is applicable to standard procedures for blood and blood filtrates where labeled carbon dioxide may be liberated by chemical or enzymic means.

Enzymatic determination of oxalic acid-C 14 in plant material

A rapid and accurate manometric method for determining the amount and specific activity of total and water-soluble oxalic acid utilizing oxalic decarboxylase from Collybia velutipes (wood-rot fungus) is described. Two Warburg flasks were used for each determination; in one of them the gas exchange was measured, and in the other the liberated C 14O 2 was trapped on a paper moistened with 1 M Hyamine hydroxide in methanol. The paper was studied in a liquid scintillation counter with high counting efficiency.