Cherenkov Counting Research Articles

Critical Role of Nucleostemin in Pre-rRNA Processing

Nucleostemin is a nucleolar protein widely expressed in proliferating cells. Nucleostemin is involved in the regulation of cell proliferation, and both depletion and overexpression of nucleostemin induce cell cycle arrest through the p53 signaling pathway. Although the presence of p53-independent functions of nucleostemin has been previously suggested, the identities of these additional functions remained to be investigated. Here, we show that nucleostemin has a novel role as an integrated component of ribosome biogenesis, particularly pre-rRNA processing. Nucleostemin forms a large protein complex (>700 kDa) that co-fractionates with the pre-60 S ribosomal subunit in a sucrose gradient. This complex contains proteins related to pre-rRNA processing, such as Pes1, DDX21, and EBP2, in addition to several ribosomal proteins. We show that the nucleolar retention of DDX21 and EBP2 is dependent on the presence of nucleostemin in the nucleolus. Furthermore, the knockdown of nucleostemin delays the processing of 32 S pre-rRNA into 28 S rRNA. This is accompanied by a substantial decrease of protein synthesis as well as the levels of rRNAs and some mRNAs. In addition, overexpressed nucleostemin significantly promotes the processing of 32 S pre-rRNA. Collectively, these biochemical and functional studies demonstrate a novel role of nucleostemin in ribosome biogenesis. This is a key aspect of the role of nucleostemin in regulating cell proliferation.

Color quench correction for low level Cherenkov counting

The Cherenkov counting efficiency varies strongly with color quenching, thus correction curves must be used to obtain correct results. The external 152Eu source of a Quantulus 1220 TM liquid scintillation counting (LSC) system was used to obtain a quench indicative parameter based on spectra area ratio. A color quench correction curve for aqueous samples containing 90Sr/ 90Y was prepared. The main advantage of this method over the common spectra indicators is its usefulness also for low level Cherenkov counting.

Radium-228 analysis of natural waters by Cherenkov counting of Actinium-228

The activities of 228Ra in natural waters were determined by the Cherenkov counting of the daughter nuclide 228Ac. The radium was pre-concentrated on MnO 2 and the radium purified via ion exchange and, after a 2-day period of incubation to allow for secular equilibrium between the parent–daughter 228Ra( 228Ac), the daughter nuclide 228Ac was isolated by ion exchange according to the method of Nour et al. [2004. Radium-228 determination of natural waters via concentration on manganese dioxide and separation using Diphonix ion exchange resin. Appl. Radiat. Isot. 61, 1173–1178]. The Cherenkov photons produced by 228Ac were counted directly without the addition of any scintillation reagents. The optimum Cherenkov counting window, sample volume, and vial type were determined experimentally to achieve optimum Cherenkov photon detection efficiency and lowest background count rates. An optimum detection efficiency of 10.9±0.1% was measured for 228Ac by Cherenkov counting with a very low Cherenkov photon background of 0.317±0.013 cpm. The addition of sodium salicylate into the sample counting vial at a concentration of 0.1 g/mL yielded a more than 3-fold increase in the Cherenkov detection efficiency of 228Ac to 38%. Tests of the Cherenkov counting technique were conducted with several water standards of known activity and the results obtained compared closely with a conventional liquid scintillation counting technique. The advantages and disadvantages of Cherenkov counting compared to liquid scintillation counting methods are discussed. Advantages include much lower Cherenkov background count rates and consequently lower minimal detectable activities for 228Ra and no need for expensive environmentally unfriendly liquid scintillation cocktails. The disadvantages of the Cherenkov counting method include the need to measure 228Ac Cherenkov photon detection efficiency and optimum Cherenkov counting volume, which are not at all required when liquid scintillation analysis is used.

Phorbol 12-Myristate 13-Acetate-dependent Protein Kinase Cδ-Tyr311 Phosphorylation in Cardiomyocyte Caveolae

Protein kinase Cdelta (PKCdelta) activation is generally attributed to lipid cofactor-dependent allosteric activation mechanisms at membranes. However, recent studies indicate that PKCdelta also is dynamically regulated through tyrosine phosphorylation in H(2)O(2)- and phorbol 12-myristate 13-acetate (PMA)-treated cardiomyocytes. H(2)O(2) activates Src and related Src-family kinases (SFKs), which function as dual PKCdelta-Tyr(311) and -Tyr(332) kinases in vitro and contribute to H(2)O(2)-dependent PKCdelta-Tyr(311)/Tyr(332) phosphorylation in cardiomyocytes and in mouse embryo fibroblasts. H(2)O(2)-dependent PKCdelta-Tyr(311)/Tyr(332) phosphorylation is defective in SYF cells (deficient in SFKs) and restored by Src re-expression. PMA also promotes PKCdelta-Tyr(311) phosphorylation, but this is not associated with SFK activation or PKCdelta-Tyr(332) phosphorylation. Rather, PMA increases PKCdelta-Tyr(311) phosphorylation by delivering PKCdelta to SFK-enriched caveolae. Cyclodextrin treatment disrupts caveolae and blocks PMA-dependent PKCdelta-Tyr(311) phosphorylation, without blocking H(2)O(2)-dependent PKCdelta-Tyr(311) phosphorylation. The enzyme that acts as a PKCdelta-Tyr(311) kinase without increasing PKCdelta phosphorylation at Tyr(332) in PMA-treated cardiomyocytes is uncertain. Although in vitro kinase assays implicate c-Abl as a selective PKCdelta-Tyr(311) kinase, PMA-dependent PKCdelta-Tyr(311) phosphorylation persists in cardiomyocytes treated with the c-Abl inhibitor ST1571 and c-Abl is not detected in caveolae; these results effectively exclude a c-Abl-dependent process. Finally, we show that 1,2-dioleoyl-sn-glycerol mimics the effect of PMA to drive PKCdelta to caveolae and increase PKCdelta-Tyr(311) phosphorylation, whereas G protein-coupled receptor agonists such as norepinephrine and endothelin-1 do not. These results suggest that norepinephrine and endothelin-1 increase 1,2-dioleoyl-sn-glycerol accumulation and activate PKCdelta exclusively in non-caveolae membranes. Collectively, these results identify stimulus-specific PKCdelta localization and tyrosine phosphorylation mechanisms that could be targeted for therapeutic advantage.

Synapsin Phosphorylation by Src Tyrosine Kinase Enhances Src Activity in Synaptic Vesicles

Synapsins are synaptic vesicle-associated phosphoproteins implicated in the regulation of neurotransmitter release. Synapsin I is the major binding protein for the SH3 domain of the kinase c-Src in synaptic vesicles. Its binding leads to stimulation of synaptic vesicle-associated c-Src activity. We investigated the mechanism and role of Src activation by synapsins on synaptic vesicles. We found that synapsin is tyrosine phosphorylated by c-Src in vitro and on intact synaptic vesicles independently of its phosphorylation state on serine. Mass spectrometry revealed a single major phosphorylation site at Tyr(301), which is highly conserved in all synapsin isoforms and orthologues. Synapsin tyrosine phosphorylation triggered its binding to the SH2 domains of Src or Fyn. However, synapsin selectively activated and was phosphorylated by Src, consistent with the specific enrichment of c-Src in synaptic vesicles over Fyn or n-Src. The activity of Src on synaptic vesicles was controlled by the amount of vesicle-associated synapsin, which is in turn dependent on synapsin serine phosphorylation. Synaptic vesicles depleted of synapsin in vitro or derived from synapsin null mice exhibited greatly reduced Src activity and tyrosine phosphorylation of other synaptic vesicle proteins. Disruption of the Src-synapsin interaction by internalization of either the Src SH3 or SH2 domains into synaptosomes decreased synapsin tyrosine phosphorylation and concomitantly increased neurotransmitter release in response to Ca(2+)-ionophores. We conclude that synapsin is an endogenous substrate and activator of synaptic vesicle-associated c-Src and that regulation of Src activity on synaptic vesicles participates in the regulation of neurotransmitter release by synapsin.

Determination of radiostrontium in environmental samples using sodium hydroxide for separation of strontium from calcium

A method was developed to separate Sr from a large amount of Ca, based on the solubility difference of Sr(OH) 2 and Ca(OH) 2 . If the determination of both 89 Sr and 90 Sr is required, then the separation of Sr from Ba is based on the difference in the solubility of Sr and Ba chlorides in HCI media. If only 90 Sr is to be analyzed by measuring 90 Y, the separation of Ba will be carried out by precipitation of Ba as BaSO 4 . Cherenkov counting by a liquid scintillation spectrometer was used to measure radiostrontium and radioyttrium activities. Chemical yield of strontium was determined with 85 Sr-radioactive tracer. The analytical method has been successfully applied to the determination of 89 Sr and 90 Sr in different environmental materials, water, soil, sediments, milk, bones, grass, algae, ash from aerosol filters, etc. The analytical quality was checked by analyzing reference materials.

CHEREN2, the Cherenkov counting efficiency by an anisotropy detection model

The commercially available liquid-scintillation spectrometers are also feasible for the detection of the Cherenkov light emitted by β-rays in transparent liquids, when the maximum-point energy of the Fermi distribution is greater than the Cherenkov threshold energy. We present a second version of the program CHEREN, which applies Poisson statistics to compute the two photomultipliers counting efficiency. We redefine previous version free parameters, including two new different coefficients into the counting efficiency equation. The Frank and Tamm theory of Cherenkov radiation is applied to compute the total number of Cherenkov light photons emitted by the β-particles along their pathways. Program summary Title of program:CHEREN2 Catalogue identifier:ADWJ Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADWJ Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:none Computers: any IBM PC compatible with 80386 or higher Intel processors Operating systems under which the program has been tested:MS-DOS and higher systems Programming language used:FORTRAN 77 Memory required to execute with typical data:45 kword No. of bits in a word:32 No. of lines in distributed program, including test data, etc.:966 No. of bytes in distributed program, including test data, etc.:7356 Distribution format:tar.gz Nature of the physical problem:Although a liquid-scintillation spectrometer can be applied to count Cherenkov light photons free of noise interference, the non-isotropic character of the Cherenkov light emission reduces the counting efficiency of the two-phototube system working in coincidence, and makes the Cherenkov light measurements comparatively much less efficient than with scintillators. However, the application of standardization techniques based on Cherenkov counting is recommend when the radioactive sample cannot be dissolved into the liquid scintillator cocktail. Also the ability to recover the radioactive sample unaltered and the possibility of eliminating low-energy contributions below the Cherenkov threshold energy are interesting aspects to be considered. Method of solution:The directional character of Cherenkov light and the amount of energy Cherenkov light needs to create one photoelectron at the photocathode are defined as two new free parameters into the counting efficiency expression. The number of photons emitted by the β-particle is computed according to Frank and Tamm theory. Additionally, the application of a range to energy relationship, which takes into account the strong deceleration of the β-particle in the medium, is required. To determine the free parameter values, the program needs the measured efficiencies for at least two radionuclides of well-known shape factors (e.g., 36Cl and 32P). Restrictions on the complexity of the problem:Computations are restricted to pure β and β- γ-emitters for which the contribution of the Compton electrons to the total Cherenkov counting efficiency is less than 2%. The comparison between the computed and experimental counting efficiencies requires one to maintain unaltered the vial material, the sample volume and the acid concentration throughout the experiments.

Determination of radioactive strontium in seawater

This paper describes the procedures of isolating strontium and yttrium from seawater that enable the determination of 89,90Sr. In one procedure, strontium is directly isolated from seawater on the column filled with Sr resin by binding of strontium to the resin from 3 M HNO 3 in a seawater, and successive elution with HNO 3. In others, strontium is precipitated from seawater with (NH 4) 2CO 3, followed by isolation on a Sr column or an anion exchange column. It is shown that strontium precipitation is optimal with concentration of 0.3 M (NH 4) 2CO 3 at pH = 11. In these conditions, 100% Y, 78% Sr, 80% Ca and 50% Mg are precipitated. Strontium is bound on to Sr column from 5 to 8 M HNO 3, separated from other elements by elution with 3 M HNO 3 and 0.05 M HNO 3. Strontium and yttrium are bound on to anion exchange column from alcoholic solutions of nitric acid. The optimum mixture of alcohols for sample binding is a mixture of ethanol and methanol with the volume ratio 1:3. Strontium and yttrium are separated from Mg, Ca, K, and other elements by elution with 0.25 M HNO 3 in the mixture of ethanol and methanol. After the separation, yttrium and strontium are eluted from the column with water or methanol. In the procedure of direct isolation from 1 l of the sample, the average recovery of 50% was obtained. In the remaining two procedures, the strontium recovery was about 60% for the Sr column and 65% for anion exchange column. Recovery of yttrium is about 70% for the anion exchange column. It turned out that the procedure with the Sr resin (direct isolation and isolation after precipitation) is simpler and faster in the phase of the isolation on the column in comparison with the procedure with the anion exchanger. The procedure with the anion exchanger, however, enables the simultaneous isolation of yttrium and strontium and rapid determination of 89,90Sr. These procedures were tested by determination of 89,90Sr on liquid scintillation counter and Cherenkov counting in 5 M HNO 3. Obtained results showed that activity of 50 mBq l −1 of 89,90Sr and higher can be simultaneously determined.

Isolation of iron and strontium from liquid samples and determination of 55Fe and 89,90Sr in liquid radioactive waste

This paper describes the method of isolating iron and strontium from liquid samples with a low concentration of ions that enables simple and rapid determination of 55 Fe and 89,90 Sr . The method consists of binding (concentrating) Fe and Sr at the cation exchanger Amberlite IR-120, their elution from cation exchanger with 4 M HCl or 8 M HNO 3, isolating Fe on the TRU extraction chromatographic column with 4 M HCl or 8 M HNO 3, and isolating Sr on the Sr.spec column with the mixture of 8 M HNO 3+2 M HCl or 5 M HNO 3. After the isolation, 55 Fe is determined by liquid scintillation counting with scintillation solution, while activity of 89,90 Sr is obtained by Cherenkov counting in 5 M HNO 3. It was shown that successive counting can be used for simultaneous determination of 89,90 Sr activity. The activity ratio of 89 Sr/ 90 Sr (up to 20:1) and vice versa does not impact the determination. 55 Fe is also determined immediately after isolation. The measurements in α,β mode can be used to verify any presence of α-emitter (americium) in the fraction of iron and to correct the result. The method was tested by determining 55 Fe and 89,90 Sr in model samples and radioactive waste samples. The paper also shows that Fe and Zn can be bound to the TEVA and TRU resins from the solutions of HCl, HNO 3, and mixture of HCl+HNO 3. The binding strength depends on the type of resin and the concentration of the acid or the concentration of acids in the mixture. These resin and acids can be used for mutual separation of Fe and Zn and their separation from other elements.

Determination in lead shields for low-level γ-spectrometry applying two independent radiometric techniques

Abstract 210 Pb radioimpurities in different lead pieces used for shielding low-level gamma-ray spectrometers have been determined through the application of two independent radiometric techniques: alpha-particle spectrometry ( 210 Po ) and Cherenkov counting ( 210 Bi ) . Associated to each technique, simple radiochemical procedures have been developed for the isolation of the radionuclides of interest and/or their adaption to the measurement conditions. These determinations are very useful in designing low-level gamma-spectrometric systems as well as in the interpretation, evaluation and even simulation of their background spectra.

Sample preparation methods for the determination of plutonium and strontium in environmental samples by low level liquid scintillation counting and α-spectrometry

SummaryTwo different methods – leaching and microwave assisted total dissolution – have been exploited for the treatment of environmental samples for the determination of plutonium and strontium. Leaching applied to reference materials demonstrated the procedure to be applicable for the recovery of technogenic Pu and Sr from environmental samples.For the measurement of the alpha emitters of plutonium, co-precipitation with calcium oxalate and ferric hydroxide and separation with anion exchange has been used. For preparation of α-spectrometry sources, co-precipitation with NdF3on a membrane filter or electro-deposition using the (NH4)2C2O4/HCl method have been tested. The beta emitter241Pu was measured by liquid scintillation counting. Pu isotope concentrations determined in the reference materials agreed well with the certified concentrations.90Sr was measured in the leachate solutions from environmental samples collected close to a nuclear facility and from reference materials, after separation from the other leached elements, by liquid scintillation counting and Cherenkov counting. The90Sr-concentrations determined in the reference materials agreed well with the certified concentrations. In the samples collected close a nuclear facility (soil, grass and sheep faeces),90Sr was found at higher levels, which could also be correlated with the location of the sampling.

Cherenkov counting of yttrium-90 in the dry state; correlations with phosphorus-32 Cherenkov counting data

We present data that illustrate some advantages of Cherenkov counting for the radioassay of 90Y in the dry state and provide recommendations concerning sample counting geometry. Slightly higher detection efficiencies and figures-of-merit were obtained when counting 90Y in the dry state in polyethylene plastic counting vials compared to the counting of 90Y in 20 ml of water in borosilicate glass vials. The effects of polyethylene plastic counting vials and sample counting geometry are compared to similar data obtained in the Cherenkov counting of 32P. Data are presented to interpret the effects of polyethylene plastic and borosilicate glass on Cherenkov counting efficiency and background counts. Applications of the Cherenkov counting of 90Y and 32P in the dry state in the biological and radiopharmaceutical sciences are foreseen as well as applications in the analysis of 90Sr( 90Y) and 32P in health physics and environmental monitoring.

Factor of merit and minimum detectable activity for 90Sr determinations by gas-flow proportional counting or Cherenkov counting

The determination of 90Sr in environmental samples can be done by using a gas-flow proportional counter ( β-counting) or a liquid-scintillation spectrometer (Cherenkov counting). In this work, we present the factor of merit (FOM) and the minimum detectable activity (MDA) for both the counters. Quantitative relationships are proposed for FOM and MDA determination.

Cherenkov Counting Efficiencies for β−-Emitters in Dry State in Glass Vials

Abstract Cherenkov counting efficiencies for standardized β−-emitters in the dry state at the centre of air-filled glass vials were measured with a liquid scintillation spectrometer. Cherenkov counting efficiencies, which are plotted as a function of the average energy of β−-particles and the internal conversion electrons, give a straight line on log–log scale.

Possibility of rapid determination of low-level 90Sr activity by combination of extraction chromatography separation and Cherenkov counting

The paper describes the examination of bonding of alkaline and alkaline-earth elements from solutions of nitric, sulphuric, acetic and hydrochloric acid on Sr.spec resin and their mutual separation. According to the obtained results, a procedure of isolation of 90Sr from natural samples has been created. It is shown that the strength of cation bonding depends on the acid applied and the solution composition. Chromatographic separation of strontium from other cations is possible by means of nitric and sulphuric acids, while it is not possible with hydrochloric acid. Similarly, chromatographic separation of potassium from strontium and other elements is possible with 5 M nitric acid. The possibility of detection of 90Sr on a low-level scintillation spectrometer by means of Cherenkov counting has been examined and the procedure of rapid determination in sediment and water samples has been created. The efficiency of a low-level scintillation spectrometer for 90Sr( 90Y) by means of Cherenkov counting has been determined. It has also been shown that it depends on the acid solution applied. The paper shows that 90Sr can be determined by means of Cherenkov counting in water in the presence of low level activity of plutonium and americium.

Improved method for the separation of radioactive strontium from various samples by mixed solvent anion exchange

Procedures for the separation and determination of90Sr in liquid samples, with cation and anion exchangers have been described. Strontium, yttrium and other cations bind to the cation exchanger and are eluted from the column by means of nitric acid. Separation of yttrium and strontium from other cations is carried out on columns filled with strong base anion exchangers in nitrate form with alcoholic solutions of nitric acid. This separation method enables the determination of90Sr through yttrium on a low-level gas flow α, β-counter, as well as through strontium on a lowlevel liquid scintillation counter by means of Cherenkov counting. Such procedures have been tested by the determination of90Sr in water, wine, medium radioactive liquid waste samples, milk and clover samples. For comparison, the determination has also been carried out by the standard method. It has been showed that the developed procedures might produce a high efficiency in strontium separation and a satisfactory accuracy of determination.

Radioactivity measurement of 188Re by Cherenkov counting

It is demonstrated that the radioactivity of 188Re, which is of current interest for the use in therapeutic applications in the field of nuclear medicine, can be precisely determined by Cherenkov counting using conventional scintillation counters, ranging from as low as background level to a 10 4 Bq level. Parameters such as sample volume, type of the counting vial, etc., which may affect the detection efficiency of this method, are systematically examined and evaluated.

CHEREN, the Cherenkov counting efficiency

A program is presented that computes the Cherenkov counting efficiency for β-particle-emitting nuclides counted in commercial liquid-scintillation spectrometers. The detection probability function for the Cherenkov light is derived experimentally for standards of 36C1 and 32P, and integrated over the energy interval between the Cherenkov threshold and the end-point of the β-particle distribution. We emphasize the importance of the shape factor forms in the computation of the counting efficiency.

Efficiency calibration of a liquid scintillation counter for 90Y cherenkov counting

In this paper a complete and self-consistent method for 90Sr determination in environmental samples is presented. It is based on the Cherenkov counting of 90Y with a conventional liquid scintillation counter. The effects of color quenching on the counting efficiency and background are carefully studied. A working curve is presented which allows to quantify the correction in the counting efficiency depending on the color quenching strength.

Efficiency calibration of a liquid scintillation counter for 90Y Cherenkov counting

Efficiency calibration of a liquid scintillation counter for 90Y Cherenkov counting