The International journal of applied radiation and isotopes最新文献

The formulas estimating initial recombination of ions created by electrons in high pressure parallel plate ionization chambers are modified and developed to comply with a modified model for recombination. Appropriate average values for restricted ionization density related parameters of recombination are derived to describe the situation of irradiation with electron or photon spectra. It is shown that these average values are related to the dose mean of the restricted ionization density (cut-off energy 500 eV) in methane based tissue equivalent gas. An experimental comparison between the predictions of the modified model and Lea's model for electron recombination is presented and the modified model shows a closer agreement with experiment in all situations studied. The modified model predicts the experimentally observed currents to within 0.1% over the photon energies studied (60–1225 keV) and over all high field strengths applied to the chamber, at a constant pressure of 8 atm.

Two methods were developed for the synthesis of [2-¹¹C]5,5-dimethyl-2,4-oxazolidinedione ([2-¹¹C]DMO) for use with positron emission tomography to measure regional cerebral tissue pH in vivo in man. In both methods, A and B, [2-¹¹C]dimethyl carbonate (DMC) was prepared from [¹¹C]phosgene and excess of sodium methoxide in methanol containing 2-hydroxyisobutyramide (HIBA). In method A, an excess of DMC was used as a carrier, while in method B none was used. In both methods, the [2-¹¹C]DMC solution was then heated for 10 min at 150°±2°C causing the reaction of [2-¹¹C]DMC with HIBA to yield [2-¹¹C]DMO with a radiochemical purity of greater than 99%. Method A gave significantly higher radioactive yields, a pure organic product, but lower specific activities. Flash chromatography was used for the separation and purification of [2-¹¹C]DMO prepared by method B.

We studied the effect of powdery silica on radiation removal of SO₂ and NOx from mixtures of SO₂, NOx, water vapour, oxygen and nitrogen under irradiation by electron beams of 1.5 MeV at 120°C. The SO₂ and NOx concentrations decreased when powdery silica was fed without irradiation. Decrements of SO₂ and NOx concentrations were markedly enhanced when powdery silica was fed together with the irradiation. The enhancement of SO₂- and NOx-removal is attributed to the adsorption of SO₂ and NO on the water-covered surface of powdery silica, and the effective removal of NO₂ due to the reaction with water adsorbed on the surface of powdery silica. The results obtained show that the addition of powdery silica under irradiation is an effective method of enhancing the removal of SO₂ and NOx.

A review is given of the calculations of scattering corrections in 2πα counting. The experimental correction factors appear to be in reasonable agreement with the classical, multiple- scattering theory of Williams.

The dependence of alkali halide crystal lyoluminescence on crystal lattice defect concentration has been studied using the rotating-disk method. It is shown that lyoluminescence intensity changes in proportion to changes of F-center concentration in a crystal. It is also demonstrated that by gradually dissolving the crystal in the form of a disk, while rotating it with a constant angular rate around its axis of symmetry, it is possible to determine the defect distribution over the crystal depth with a resolution of the order of 1 μm according to measurements of lyoluminescence intensity.

An antibody has been labelled with generator produced yttrium-90 (⁹⁰Y) via a chelating group (DTPA) covalently attached to the protein. An average yield for protein labelling of 76% was obtained. The blood clearance of iodinated and ⁹⁰Y labelled antibody is similar in rats and mice. However, in contrast to iodine, the yttrium label accumulates in the liver after release from the protein.

A new design for a liquid scintillation counter based on a flat-bed geometry is described. Micro-samples are dried or filtered onto transfer membranes or glass fibre filters in a 6 × 16 matrix, compatible with 96-well micro-titration plate filtration assays of labelled cells. A prototype counter without lead shielding had low background countrates (2–3 cpm for ³H) giving a figure of merit of 1325 (and 1292 for ¹⁴C). Only 5–15 ml of scintillant/96 samples are required and thus the volume of radioactive waste is low.

Monte Carlo calculations of fast neutron flux distributions have been made for ²⁵²Cf, ²⁴¹Am/Be and 14 MeV monoenergetic neutron sources in a range of bituminous coals. The configurations examined were sources at the centre of a sphere, at the midpoint of the plane surface of a hemisphere and at or near the surface of a parallel-sided slab. The neutron fluxes were analysed in terms of the resultant yield of γ-rays from inelastic scattering on silicon, carbon and oxygen, which are the key reactions for determining the oxygen content of coal by processes yielding prompt γ-rays. The fast neutron spectra were found to undergo significant changes in shape as a function of distance from the source, in contrast with the assumptions made in the model developed by Wormald and Clayton. ⁽¹⁾ However, the ratios of the response functions for inelastic scattering by the critical elements were found to be very insensitive to the type of coal, indicating that oxygen analyses could be performed for a given configuration and neutron source by using calibration factors derived from a single calculation or benchmark experiment on a coal of intermediate composition. The calculations described also provided information on the yield and spatial distribution of thermal neutrons from the selected sources.

(o)-[⁷⁷Br]bromohippuran (BHIP) was developed as renal tubular function agent due to its favourable chemical and physical properties and compared to (o)-[¹³¹I]iodohippuran (IHIP). Renograms obtained from baboons were compared and absorbed radiation dose calculations performed. Although BHIP showed a delayed kidney uptake and washout pattern, good kidney clearance of the radionuclide was obtained after 30 min. Radiation dose values for BHIP were markedly lower than for IHIP indicating that larger activities of BHIP could be administered to increase counting statistics. BHIP imaging in normal volunteers did however not substantiate the favourable behaviour obtained in the primate.