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At least 1,315 records · Page 73Linked to original sources
PubMed1983

Heavy ion action on yeast cells: inhibition of ribosomal-RNA synthesis, loss of colony forming ability and induction of mutants.

The action of heavy ions (Ar to U) accelerated to specific energies up to about 10 MeV/u (u=atomic mass unit) on different functions of yeast cells was studied. Ribosomal-RNA synthesis is inhibited according to a single-hit mechanism. Inactivation cross-sections were linearly related to the ratio of the squares of the effective charge Z* and the velocity of the ions. It is concluded from the analysis that the range of the most energetic delta-electrons is larger than previously assumed. There is no such dependence for survival and induction of mutants. In both cases cross-sections increase with the ion's specific-energy indicating an important contribution of long-range delta-electrons. The analysis shows that diploid yeast is not killed by a single-hit mechanism even by very heavy ions if the track width is too small. The relative importance of the penumbral region is even more pronounced with the more sensitive strains.

Argon↗
PubMed1988

Production of 75Br via the 78Kr (d,n alpha)75Br reaction.

The production of 75Br by the 78Kr (d,n alpha)75Br reaction using a 21.5 MeV deuteron beam was investigated. With our 78Kr gas target, the production yield was found to be 5.9 +/- 0.9 mCi/microA at saturation. The major impurities in the 75Br product were 76Br and 77Br which amounted to about 6 and 2.5% respectively, at EOB. Sufficient amounts of 75Br could easily be prepared by this method for use in chemistry and animal experiments but deuteron energies greater than 20 MeV are required.

Bromine Radioisotopes↗
PubMed1988

An extension set for 81Rb-81mKr solution generators for lung ventilation studies.

For 81Rb-81mKr solution generators, an extension set has been developed, which strips the 81mKr from the liquid eluate with a stream of air for use in lung ventilation studies. Via a three-way valve the 81Rb-81mKr solution generator can be operated alternately in the perfusion mode or in the ventilation mode. Measurements and calculations have been performed to get more insight into the parameters of interest for an optimum design of the extension set and its operation conditions.

Humans↗
PubMed1991

A 81Rb/81mKr generator made by ion implantation.

Isotopically pure 81Rb was implanted in plastic foils, and the daughter 81mKr was eluted quantitatively by air or by a 0.9% NaCl solution. The elution yield, the purity of the 81mKr, and the washing-out losses of 81Rb were studied as functions of the implantation density. It was seen that the densities below 5 x 10(12) Rb atoms/cm2 provide a high yield for elution both by liquid and air. The first 100 MBq implantation-type generator was tested by making a lung-ventilation study in man.

Krypton Radioisotopes↗
PubMed1991

Integral excitation functions for natKr + p up to 116 MeV and optimization of the production of 81Rb for (81m)Kr generators.

Effective cross-sections for the production of 79,81,81m,82m,83,84,84m,86Rb, (77,79,85m)Kr and 77,82Br in the bombardment of natKr with protons were measured from threshold up to 116 MeV. Thick-target production-rate curves based on the measured integral excitation functions were also derived for 81,82m,83,84,86Rb, and the optimum incident energy for the production of 81Rb/(81m)Kr, as a function of the target thickness in MeV, was determined. Geometry-dependent hybrid-model calculations performed by means of the computer code ALICE/85/300 were found to be in good agreement with the experimental results as well as the derived thick-target production-rate curves.

Krypton Radioisotopes↗
PubMed1991

Production of 6.5 h 82mRb via the 82Kr(p, n)-process at a low-energy cyclotron--a potential substitute for 82Rb.

The production of 6.5 h 82mRb, a potential substitute for generator-produced 1.2 min 82Rb in myocardial blood flow studies, is discussed. Using a 82Kr gas target and a low-energy cyclotron it is possible to obtain greater than 100 mCi (greater than 3.7 GBq) of high purity 82mRb. Results of radiation dose calculations for 81Rb/81mKr, 82Rb and 82mRb are reported.

Coronary Circulation↗
PubMed1990

Comparison of four commercially available 81Rb-81mKr generators: quality testing using a breathing lung phantom.

Four commercially available 81Rb-81mKr generators, including their elution systems, were compared. Considerable differences in useful output between the various generators were found. When a standardized elution system was used, the differences became much less. Differences in the tubing and inaccuracy of the flow meters were found to be the major causes of the original differences. The user should be aware of a loss of output that may occur when the generator is eluted with dry air.

Humans↗
PubMed1996

Direct radiofluorination of dopamine: 18F-labeled 6-fluorodopamine for imaging cardiac sympathetic innervation in humans using positron emission tomography.

Fluorine-18 labeled fluorodopamine (FDA) was synthesized by the direct fluorination with [18F]F2 [produced by the nuclear reaction 18O(p,n)18F] of dopamine in anhydrous hydrogen fluoride containing boron trifluoride at -65 degrees C. Reverse-phase high-performance liquid chromatography (HPLC) was used to separate [18F]6-FDA from the reaction mixture containing 18F-labeled 2- and 5-FDA. The radiochemical yield of [18F]6-FDA, with respect to [18F]F2, was 10 +/- 2% at the end of the 120-min synthesis from EOB1. The specific activity of [18F]6-FDA at the end of synthesis, 10 +/- 1.5 Ci/mmol, is sufficiently high that the amount of 6-FDA associated with the infusion of a dose of 5 mCi of [18F]6-FDA over 3 min into a 50-kg human (0.5-0.7 microgram/kg/min) is considerably lower than therapeutic doses (2-10 micrograms/kg/min) of dopamine.

Chromatography, High Pressure Liquid↗
PubMed2006

Kr-81m calibration factor for the npl ionisation chamber.

A general method has been developed for the measurement of the activity concentration of 81mKr gas. Due to its short half-life, 13.1s, this gas has to be eluted from a 81Rb/81mKr generator. The 81Rb parent has a half-life of about 4.6 h. The calibration was done in two steps: firstly, a gamma-ray spectrometer was calibrated using 51Cr and 139Ce sources, nuclides with gamma-ray energies bracketing that of 81mKr (190.5 keV). The measurement geometry was equivalent to that of the 81mKr measurement; the sources were inserted into two collimated PTFE tubes in front of the gamma-ray detector. Secondly, a calibration factor for the NPL radionuclide calibrator was determined with a specially designed ionisation chamber insert. The 81mKr gas passed in front of the gamma-ray detector in PTFE tubing before and after entering the ionisation chamber. The calibration factor for 81mKr in the radionuclide calibrator with this geometry was independent of the gas flow rate within determined limits. The analytical calculations of the activity determination, uncertainties and measurement criteria are discussed.

Algorithms↗
PubMed2006

On-site gamma-ray spectroscopic measurements of fission gas release in irradiated nuclear fuel.

An experimental, non-destructive in-pool, method for measuring fission gas release (FGR) in irradiated nuclear fuel has been developed. Using the method, a significant number of experiments have been performed in-pool at several nuclear power plants of the BWR type. The method utilises the 514 keV gamma-radiation from the gaseous fission product (85)Kr captured in the fuel rod plenum volume. A submergible measuring device (LOKET) consisting of an HPGe-detector and a collimator system was utilised allowing for single rod measurements on virtually all types of BWR fuel. A FGR database covering a wide range of burn-ups (up to average rod burn-up well above 60 MWd/kgU), irradiation history, fuel rod position in cross section and fuel designs has been compiled and used for computer code benchmarking, fuel performance analysis and feedback to reactor operators. Measurements clearly indicate the low FGR in more modern fuel designs in comparison to older fuel types.

Gases↗
PubMed2005

Characterisation of dentin surfaces processed with KrF excimer laser radiation.

In the present work, the surface microtexture and chemical changes induced in human dentin by laser processing with KrF excimer laser radiation using fluences ranging from 0.5 to 20 J/cm2 were studied by SEM, XPS and FTIR. Two distinct behaviours were observed in the evolution of surface topography. In some samples, the laser-treated surface remained flat, independently of the fluence used. It was covered by a layer formed of redeposited ablation particles, which occluded the dentinal apertures. In other samples the surface topography depended on radiation fluence. When the fluence was lower than 1 J/cm2, preferential removal of intertubular dentin occurs, producing a columnar structure in which the columns are essentially formed of peritubular material. If the fluence exceeded 1 J/cm2 the processed surface was flat and covered with resolidified material. Despite these topographic changes, the dentin was not significantly affected by the laser treatment. The observed behaviour can be explained by differences in the constitution of dentin.

Carbon↗
PubMed2005

A new compilation of the atmospheric 85krypton inventories from 1945 to 2000 and its evaluation in a global transport model.

This paper gives the yearly (85)Kr emissions of all known reprocessing facilities, which are the main sources of (85)Kr in the atmosphere since 1945, for the years 1945 until 2000. According to this inventory 10,600 PBq (Peta=10(15)) of (85)Kr have been globally emitted from the year 1945 until the end of 2000. The global atmospheric inventory at the end of the year 2000 amounts to 4800 PBq. These emissions have been incorporated into the ECHAM4 atmospheric general circulation model as point sources. Monthly mean model results are compared with measurements made at different locations and times. The influence of each source on the measured concentrations at various locations is studied. The calculated concentrations are found to give reasonably good agreement with the observations, indicating that the emission inventory is realistic. Although, at all northern hemispheric observation sites the model tends to slightly overestimate the concentrations. A possible reason for this overestimation can be found in model features (coarse resolution in time and space). The most prominent discrepancy that is consistently repeated at all northern hemispheric stations occurs in the early 1990s. This could most likely be related to an overestimate of sources. Possibly, the Russian emissions declined earlier than assumed in the current database. Another discrepancy between observations and simulations indicating an incompleteness of the release data is found at some southern hemispheric sites. The variability of their observations could only be explained by regional sources. However, several spikes occur after 1992 when no reprocessing facility is known to be in operation in the southern hemisphere. Production of isotopes for radiopharmaceuticals like technetium-99m from highly enriched uranium is the most likely explanation.

Air Movements↗
PubMed2005

Comparison of some vibrational features of FArH...Rg and FHc...Rg complexes (Rg=He, Ne, Ar, Kr).

The shift in the harmonic vibrational frequency of the ArH stretch of FArH on formation of the linear FArH...Rg complexes (Rg=He, Ne, Ar, Kr), and of the FH stretch on formation of the linear FH...Rg complexes, has been determined by ab initio computations. These shifts are in agreement with predictions from a model based on perturbation theory and involving the first and second derivatives of the interaction energy with respect to displacement of the ArH (FH) bond length from its equilibrium value in the monomer. In the FH...Rg dimers, small blue shifts were obtained for the He and Ne complexes and red shifts for those with Ar and Kr. In the FArH...Rg dimers, blue shifts were obtained for all four complexes. These vibrational characteristics are rationalized by considering the balance between the interaction energy derivatives obtained from the perturbative model. The bond length changes on complexation are also well predicted by the model. Our computations were restricted to the linear geometry since the objective was to investigate the validity of the perturbation model and to illuminate the causes of the red and blue shifts.

Argon↗