Low-background Counter Research Articles

Determination of total activity by liquid scintillation counting and its application to aqueous effluent samples

An analytical method for determining total activity in water samples is described. The method depends on the direct relationship between the average energy deposited in a liquid scintillator solution and the channels ratio recorded for two different portions of the total energy spectrum. Calibration curves are constructed using single energy beta emitters. Samples are first counted at low gain for medium to high energy activity, followed by a second count at high gain to record total activity. Results obtained by this method for both synthetic and reactor effluent samples were quantitative (3–7%) compared with results obtained by low-background beta counting (42–100%).

High efficiency gamma radiation detection in clinical radioimmunoassays by liquid scintillation counting with “LSC gamma vials”

A polycrystalline sodium iodide detector (LSC Gamma Vial) has been developed which allows high efficiency counting of gamma emitting radioisotopes in liquid scintillation counters. The adaptor will fit any standard liquid scintillation counter. The LSC Gamma Vials allow I-125 and Co-57 to be detected in a standard liquid scintillation counter with counting efficiencies of 74% and 54% respectively, as compared to that of conventional gamma counting equipment. Even higher comparative efficiencies (> 100%) were obtained when the standard LSC coincidence circuitry was negated. This detector offers counting efficiency that is relatively independent of volume, has good count rate linearity, and exhibits low background count rates.

A position sensitive proportional counter for a beta-ray spectrometer

A position sensitive proportional counter employing resistive charge division was constructed for use in the focal plane of an iron-free π√2 beta-ray spectrometer ( r 0 = 75 cm). The momentum range measured at a time was about 4% and the relatively good linearity was obtained. The momentum resolution (fwhm) obtained was 0.046% at 1 MeV and 0.063% at 130 keV. The very low natural background counts were also obtained.

A low-background beta counting arrangement

An improved low-background counter suitable for the measuring of beta samples has been described in the present paper. For eliminating the background radiation there has been used a liquid scintillation detector. The anticoincidence stage is carried out by diodes. As a result of series measurement there has been measured a background rate of 0.3 pulse/minute.

318. Identification of some peaks in spectrum of characteristic losses of electron energy in tungsten: E F Chaykovskiy et al, Fiz Tverd Tela, 15 (6), 1973, 1947–1948 ( in Russian)

This paper discusses the arrangement of a 180° beta-spectrometer to give a low background for the study of Compton electrons ejected from a target by a collimated beam of gamma-rays.The effects of scattering at those spectrometer walls which do not lie within the shadows cast by its defining slits have been investigated. The importance of scattering of electrons at these walls is shown.An arrangement giving a low background counting rate which varies only slowly with energy setting is described.

Analytical use of neutron-capture gamma-rays

Certain elements which are not possible to detect with conventional neutron activation analysis can be measured using thermal neutron-capture gamma-ray analysis. The use of a curved neutron guide at the High Flux Reactor, Grenoble, with a thermal neutron flux of 1.5·1010n·cm−2·sec−1 and the advantage of a low-background counting system (Ge(Li) detector) far from the reactor core are described. Experimental detection limits of a number of elements are given for the low-energy and the high-energy regions. Some applications of the capture gamma-ray method in the whole energy range are studied and are briefly discussed.

Tritium measurements with a new liquid scintillation counter

Abstract A new concept in liquid scintillation counting has been employed in developing an instrument for the purpose of quantitatively measuring low specific activity tritium samples. The instrument design differs from present commercial instrumentation in that it utilizes electronics that measure fast-pulse time intervals rather than performing pulse height analysis. The liquid counter was built to accomodate samples as large as 100 ml of solution. The solutions can be counted as a combination of water and scintillator or as pure benzene synthesized from water. As much as 20 g of water can be counted directly as a solubilized cocktail or an equivalent of 66 g of water converted to benzene. Direct counting of aqueous cocktails can be accomplished to sensitivity levels below 10 T.U. Tritiated benzene samples of 25 ml volume have been counted at 53% counting efficiency with background count rates contributing less than 1.75 c/m. This new instrument utilizes massive graded shielding and an electronic guard to minimize external radiation for low background counting.

Measurements of low-level radon for the determination of radium in marine carbonates

A precise determination of the extremely low concentration of radium in marine carbonate samples via 222Rn counting using a ZnS(Ag) scintillation chamber was described. Carbonate sample was dissolved with hydrochloric acid and the solution was sealed in a Curie bottle for the period of accumulation of 222Rn from 226Ra. The radon in the bottle was separated from the solution and collected in a trap cooled with liquid nitrogen. Finally the radon was transferred to the scintillation chamber which is coated with a thin layer of ZnS(Ag) powder. The luminescence signals by alpha rays were well discriminated from background. Advantages of this method are as follows; its simple and reliable operation, low background count (4.5±0.5cph) and low detection limit of I × 10-14 g Ra. Some results of radium content determinations of modern and fossil shell samples are reported.

Miniature low-background counters for measurement 37Ar and 39Ar : A V Fisenko and E M Kolesnikov, Prib Tekh Eksper, No 6, 1971, 62–63 ( in Russian)

Miniature low-background counters for measurement 37Ar and 39Ar : A V Fisenko and E M Kolesnikov, Prib Tekh Eksper, No 6, 1971, 62–63 ( in Russian)

Polyriboadenylate polymerase and its relationship with RNA polymerase.

POLYRIBOADENYLATE polymerase1 is a ubiquitous enzyme whose biological role is not fully understood. Recently, the inhibition of poly A polymerase in Escherichia coli infected with T-even phages2 was tentatively related to the concomitant arrest of the synthesis of macromolecule in the bacterial host3. Its function might be further elucidated if a conditional lethal mutant could be found in which poly A polymerase is temperature sensitive. Screening for such a mutant among a set of ts mutants unable to perform protein synthesis at high temperature was undertaken by Dr G. Tocchini-Valentini using techniques already described4. 1 ml. of tryptone broth containing 5 × 108 cells of any one of the mutant derivatives of E. coli D14 (Hfr C met−RCrel) was sonicated and mixed with 1.5 ml. of 20 mM Tris (pH 9.5), 4.9 g/l. of magnesium acetate, 20 mg/l. deoxyribonuclease (ribonuclease free, Sigma), 10 mg/1. tRNA (from E. coli, General Biochemical), 55 mg of 14C-ATP (New England Nuclear) at a specific radioactivity of 0.5 mCi/mmole. This was done in duplicate: one preparation was then incubated for 20 min at 30° C, and the other at 42° C. Incubation was stopped by the addition of an equal volume of 10 per cent trichloroacetic acid (TCA) and the samples were filtered on ‘Millipore’ filters and counted in a gas flow low-background counter. To check that the TCA insoluble product from this crude extract was really poly A, a control was performed using a-32P-ATP, hydrolysing the precipitate with alkali and checking that all the radioactivity was recovered after paper electrophoresis (in acetate buffer, pH 3.5) in the AMP spot. In a set of 200 ts mutants unable to synthesize protein at high temperature, three exhibited temperature sensitive poly A polymerase activity. They were crossed and gave no wild type recombinants. Successive experiments were done using one of the three which we call C134 (see Table 1).

Biomedical Applications of Avalanche Semiconductor Detectors

The attractiveness of silicon avalanche radiation detection systems lies in the following properties: (1) Extremely low noise and low background counting capability, which is maintained to temperatures as high as 100°C, without resorting to coincidence techniques. (2) Sensitivity to virtually the entire range of nuclear radiations and energies with highest efficiency concentrated in the low energy or soft radiation region without requirement for cooling. (3) Ruggedness and miniaturizeability-a characteristic shared with other semiconductor detectors--but, in addition, providing a larger degree of usefulness in extra-laboratory applications due, primarily, to the high signal level from the detector. These characteristics make avalanche systems potentially quite valuable in nuclear medicine, particularly for in vivo detection of lower energy radiations. This paper will describe a program that was undertaken to fabricate ten prototype avalanche detector instruments for collaborative research purposes with investigators in the fields of nuclear medicine and radiobiology. All ten instruments are currently in the hands of such researchers. The specific areas of investigation are varied and interesting, with a number being rather exciting from the standpoint of being new accomplishments, i.e., avalanche technology appears to be making possible some measurements and procedures not considered feasible heretofore. Examples of specific applications being investigated are transmission bone scanning, tumor detection and diagnosis (opthalmic and skin types), organ scanning by x-ray fluorescence techniques, tooth enamel density measurements and soil water content and pressure determinations. Some very preliminary results are available on several of the above studies.

Reaction mechanisms in 75As + n system

Cross sections for the (n, 2n), (n, α) and (n, p) reactions on 75As at an incident neutron energy of 14.2 ± 0.2 MeV have been measured using the activation technique and a low back-ground gamma counting set-up consisting of a well-type NaI(Tl) scintillation spectrometer. The values obtained are: 75As(n, 2n) 74As: 1170 ± 117 mb; 75As(n, α) 72Ga: 13.6 ± 1.6 mb; 75As(n, p) 75mGe: 8 ± 1 mb; 75As(n, p) 75gGe: 16 ± 2.4 mb. The experimental cross sections for the (n, 2n) and (n, α) reactions show good agreement with the theoretical values calculated on the basis of the statistical model with a level density parameter, a = 1 8 A . In the case of 75As(n, p) 75m,gGe, however, the measured total cross section and isomeric ratio deviate considerably from the statistical predictions indicating direct interaction contribution to the (n, p) reaction.

A high resolution scanning device for determining the distribution of weak beta activity in a planar surface

A scanning device is described which allows accurate localization in one dimension of the distribution of weak beta radiation (14C and 35S) over a planar surface. A single uncooled photomultiplier tube is used with a very small anthracene crystal to achieve both high detection sensitivity and a low background counting rate. Methods of cutting small anthracene crystals and of making rectangular slit collimators of 0·1 mm width are described; the latter is adaptable to other designs. A geared drive from a constant speed motor moves the combined photomultiplier, crystal and collimator system over the labelled surface, and the distribution of activity is recorded automatically on a chart recorder. For a collimator 0·2 mm wide and 0·7 mm deep moving 0·7 mm above a straight planar edge, the instrument's resolution is 0·54 mm while the comparable value derived geometrically is 0·4 mm.

Search for tri-neutrons

A search for bound tri-neutrons in the reaction 7Li(n, 3n) 5Li has been made with neutrons produced by a 55 MeV proton beam incident on a thick metallic lithium target. The detection of the tri-neutron was attempted with the reaction 138Ba( 3n, n) 140Ba, whose yield of 140La, the β-decay product of 140Ba, was measured with a low-background counting apparatus. No evidence for the existence of the bound tri-neutron was found within the limits of experimental error. The upper limit was determined at 1 mb for the total cross section of the reaction 7Li (n, 3n) 5Li at the neutron energies E n ≈ 14–19 MeV, where its values were expected to become the highest.

Fallout caesium-137 and potassium in new-born infants.

New techniques of low background counting have made possible the measurement of intake and retention of natural potassium and caesium-137 in infants. The biological half-lives of both potassium and caesium-137 are from 5 to 10 times lower than the corresponding values in adults.

STRUCTURAL BASIS FOR INHIBITION OF PROTEIN SYNTHESIS BY EMETINE AND CYCLOHEXIMIDE BASED ON AN ANALOGY BETWEEN IPECAC ALKALOIDS AND GLUTARIMIDE ANTIBIOTICS

The therapeutic properties of the ipecac alkaloids in the treatment of certain dysenteries and their effectiveness as emetics and expectorants was recognized as early as the 17th century.1 (-)-Emetine, an active principle of ipecac, was reported to be an amebicidal agent by Vedder2 and recently has proved beneficial in the therapy of nonspecific granulomas.3 The present communication will show that emetine is a potent inhibitor of protein synthesis in mammalian and other cells, a mode of action which may account for its therapeutic and toxic properties. The glutarimide antibiotics, of which (-)-cycloheximide is the best known member, are derived from various species of Streptomyces. These compounds also inhibit protein synthesis and exert amebicidal, antitumor,5' 6 and fungicidal7 actions. An analogy between the glutarimide antibiotics and the ipecac alkaloids will be demonstrated in this paper based on (a) similarities in their mode of action, (b) their configurational resemblances, and (c) their structure-activity relationships. The analogy provides a structural basis for the inhibition of protein synthesis by the ipecac and glutarimide compounds and suggests new pharmaceutical preparations of potential value. Methods and Materials.-Protein and polyphenylalanine synthesis by extracts of different species was measured by the procedure of Lamfrom,8 for rabbit reticulocytes; of Downey et al.,9 for Saccharomyces cerevesiae; of Nirenberg and Matthaei,10 as modified by Nathans et at.,11 for E. coli; and of Penman and Summers,2 for HeLa cells. Components of the reaction mixtures are described in the legend to Table 1. Following the period of incubation, reactions were terminated by addition of 5% TCA (trichloroacetic acid) and the acid-insoluble material was washed by the procedure of Siekievitz.14 The precipitates were collected on Millipore membrane filters, and the radioactivity was determined in a Nuclear-Chicago low-background counter with an efficiency of 21% for C14. The transfer reaction was assayed in extracts of rat liver as described by Gasior and Moldave.13 (- )-Emetine and (-)-N-methylemetine were kindly provided by Dr. N. Whittaker of the Wellcome Laboratories, Kent, England; (-)-cephaeline and (+)-Omethylpsychotrine by Sandoz, Ltd., Basle; (-)-2,3-dehydroemetine and (+ )-1,2,3,4,5,11btrisdehydroemetine by Dr. A. Brossi of Hoffmann-La Roche, Nutley, N.J.; and (-+)-isoemetine by Dr. J. Elks of the Glaxo Laboratories, Middlesex, England. E. coli B sRNA was obtained from Nutritional Biochemicals, poly U (polyuridylic acid) from the Miles Laboratories, and radioisotopes from New England Nuclear. C14-phenylalanyl-sRNA and C14--leucyl-sRNA were prepared enzymatically by the procedure of von Ehrenstein and Lipmann.15 Coliphage MS2 RNA was a gift from Dr. D. Nathans. Inhibition of Protein Synthesis by Emetine.-Species specificity: The effect of emetine on protein synthesis in certain mammalian cells, yeast, and plants is shown in Table 1. Emetine can effect a 50 per cent inhibition of protein synthesis in HeLa cells and gametophytes of Anemia phylitidis at media concentrations of less than 10-611M. Under these in vivo conditions, emetine is concentrated 10- to 20fold by the cells. Protein synthesis in cell-free extracts prepared from HeLa cells and reticulocytes was inhibited by 50 per cent at concentrations of 8 X 10-5 M and 2 X 10-5 M, respectively.

Low background counting of betas and alphas with silicon detectors

A comprehensive study of the use of silicon detectors for low background counting of charged particles is described. A discussion of the effect of electronic noise on the beta detection efficiency and background is included along with experimental measurements of detection efficiency. Detailed measurements of background, with and without shielding and anticoincidence umbrella, are presented. The performance of silicon surface barrier detectors is compared with that of a conventional gas flow counter and it is shown that for sample sizes less than 1″ in dia., silicon detectors have a number of distinct convenience and performance advantages, but are presently handicapped by cost and fragility considerations.

Cholesterol formation by granulosa and thecal cells of equine follicle.

Granulosa and thecal cells were separated from the estrous follicle of an equine ovary. The individual cell types were determined to be essentially homogeneous by microscopic examination, although the thecal layer contained both theca interna and externa cells. The 2 classes of cells were incubated with acetate-l-C in vitro and labeled cholesterol was isolated and crystallized to constant specific activity. (Endocrinology 78: 214,1966) T in vitro metabolism of acetate-1-C by isolated granulosa and thecal cells of the equine ovarian follicle was studied in an effort to evaluate the ability of these individual cell types to form steroid hormones. The conversion of radioactive acetate to steroids and cholesterol by the perfused porcine ovary (1) and by the human ovarian follicle in vitro (2) has been described but the activities of the individual cells that comprise the follicle have not yet been reported. Techniques for the separation of granulosa and thecal cells have been developed (3) and the conversion of acetate-1C to labeled cholesterol by these cells is the subject of the present communication. Materials and Methods The ovaries were obtained from a mare at the time of sacrifice and a ripe follicle was dissected from one ovary. The appearance of the follicle and the old corpus luteum in the contralateral ovary indicated that the animal was in estrus. This was further substantiated by hormone assay of the follicular fluid (Table 1) carried out as previously described (4). The follicle was 4X4.5X5 cm and contained 40 ml of follicular fluid. The follicle was incised and the granulosa (184 mg) separated from the thecal layers (268 mg) as previously described (3). The isolated granulosa cells were essentially homogeneous on microscopic examination and the thecal layer consisted of both theca interna and externa cells denuded of the granulosa. The Received June 28,1965. This work was supported in part by Grant AM 05739 from the USPHS. thecal layer was minced with scissors prior to use. The separated cells were incubated with 50 nc of acetate-l-C (278 jic/mg) in Krebs phosphosaline buffer at pH 7.4 for 3 hr with 10 /M DPN and 10 MM ATP. The incubation was stopped by the addition of 10 volumes of hot acetone and the mixture was filtered. The acetone-aqueous mixture was evaporated under reduced pressure and the aqueous residue was extracted 3 times with 6 volumes of CHC13. The remainder of the extraction was carried out as previously described (2). A pentane-90% methanol partition separated the more polar steroids from the sterols and lipids. The 90% methanol extract was partitioned into neutral and phenolic fractions which were subjected to column and paper chromatography. The pentane fraction was subjected to digitonin precipitation. The digitonin-precipitable material was mixed with carrier cholesterol, the dibromide formed and free cholesterol regenerated (1). The cholesterol was crystallized to constant specific activity from methanol. Radioactivity was measured in duplicate in a Nuclear-Chicago low background counter with an efficiency for C of 36 %, and cholesterol was measured by the Lieberman Burchard reaction (5).

Concrete low-background counting enclosure.

A massive concrete low-background gamma-ray counting enclosure has recently been constructed at the Health Physics Department, Lawrence Radiation Laboratory (University of California), Berkeley. Walls and roof are 4–5 ft thick; inside dimensions are 23.5 × 11.5 × 11.5 ft. A substantial effort was made to secure materials adequately low in radioactivity for the concrete. Of primary concern were the concentrations of potassium, uranium and thorium in possible low-radioactivity sources of aggregate and cement materials. Geologic considerations indicated that ultramafic igneous rocks are the lowest in these radioisotopes. An examination was conducted of possible sources of low-radioactivity aggregate material; samples were analyzed for radioactivity on a 100-channel gamma-ray spectrometer. Evaluation of the spectrometer analyses and economic considerations resulted in the choice ofserpentinized ultramafic rock from a deposit in the foothills of the Sierra Nevada as the source of low-background aggregate. Raw materials from twelve portland cement plants in California, and finished products from 114 plants in the United States and Canada, were also examined for radioactivity by gamma-ray spectrographic analysis. Cement from a producer on Vancouver Island, British Columbia, was chosen as the lowest-radioactivity cement product commercially available. The completed enclosure furnishes a nearly twofold reduction in background in comparison with the previous counting arrangement. Equally important, the thick concrete shield with its included water of hydration keeps the present level of radioactivity non-fluctuating, whereas the background in the previous counting arrangement varied in proportion to the external fast-neutron flux produced by nearby accelerators. Future installation of a 1-ft-thick ultra-low-background liner and (or) an approximately 1/8-in.-thick lead membrane on the inside surface of the enclosure should significantly reduce the present background. A comparison of costs indicates that to shield a similar-sized counting space with steel of equivalent attenuation and low-background characteristics would cost (in place) about four times as much as the existing concrete structure.

Gas-Liquid Chromatographic Method for Determination of Fat-Soluble Vitamins. III. Evaluation of a Vacuum Distillation Procedure for Vitamin E Isolation, Using C-14 Labelled Alpha-Tocopheryl Acetate

Abstract Alpha-tocopheryl acetate, carbon-14 labelled in the methyl group at the two position, was used to determine the stability and recovery of the vitamin during vacuum distillation (140–160°C, and 0.020 mm Hg pressure, 60 minutes). Evaluation was based on measurements of radioactivity with a liquid scintillation spectrometer and a lowbackground Geiger counter. Recoveries of 20 mg of the pure compound were nearly quantitative (97%). Recoveries of the tocopheryl ester added to lard, “stripped” of vitamin E, at 0.5 mg/g or less and to butter at 0.1 mg/g were 98 and 82%, respectively. Results of the differential counting technique suggest that the ester is increasingly unstable at temperatures exceeding 160° and that a molecular rearrangement probably takes place.