International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes最新文献

Total photon cross-sections have been measured in 15 compounds and in 3 selected elements at 7 different photon energies in the range of 145–1120 keV on a good geometry set-up using a NaI(Tl) detector coupled to a ND 60 multichannel analyser. The results include some data points which have not been previously reported. From the measured total cross-sections per molecule of the compound, atomic cross-sections in elements have been extracted using the mixture rule. The derived atomic cross-sections have been compared with the theoretical Hubbell-Scofield values and of Storm and Israel. In addition, the experimental total photon cross-sections of the three selected elements are compared with those derived from measurements on the compounds containing the selected elements. A good agreement is observed amongst the different values, within experimental error.

A simple procedural change for the synthesis of [¹⁸F]FDG has been used to recover [¹⁸O]water by direct distillation. The [¹⁸O]water thus recovered is reusable to produce [¹⁸F]fluoride without further purification. The recovery of [¹⁸O]water is reliable and our results are based on over 300 routine FDG preparations. The [¹⁸F]fluoride present in the target water is converted to potassium fluoride during the distillation and will be available for further reaction to complete the synthesis of FDG. The same procedure can be used to recover [¹⁸O]water in similar situations where [¹⁸F]fluoride is converted to potassium fluoride and in turn used to react with kryptofix for labeling other precursors.

A novel method for the efficient preparation of ¹¹C-radiopharmaceuticals by on-line [¹¹C]methylation using [¹¹C]methyl iodide has been developed and applied to a rapid, convenient automated system. [¹¹C]Methyl iodide is first trapped in a short column, containing an adsorber and coated substrate, which is connected to an HPLC injector. DMF is then introduced. Alternatively the substrate is added with the DMF. A whole reaction mixture can be easily injected onto an HPLC column for purification by switching the injector valve immediately after the reaction. Thus, radiochemical yields in the preparation of ¹¹C-labeled doxepin, benztropine, cyproheptadine and N-methylspiperone have been improved remarkably and the synthetic procedure simplified.

[⁹⁹Tc(phen)₃]Cl₂ was synthesized by reduction of pertechnetate with sodium borohydride in the presence of an excess of 1,10-phenanthroline and characterized by FAB mass spectrometry, magnetic susceptibility measurements, and i.r./vis/u.v. spectrophotometry. For biodistribution evaluation in mice [^99mTc(phen)₃]Cl₂ could be obtained in a radiochemical purity of 92.5% using a similar procedure. The rather hydrophilic chelate was predominantly excreted by the kidneys. Its low blood retention resulted in a heart/blood activity ratio of 4.2 at 100 min post-injection.

Measurements and analysis of the kinetics of the phenomenon of migration of polonium to the surface in lead are presented. Polonium atoms diffuse to surface because their thermodynamic potential on surface is lower than inside the lead of the raw production. The effect is very weak for the case of thermal diffusion at room temperature, but very strong when close-to-surface layer is plastically deformed for instance by cutting of the surface. After several vacuum-remelting processes all the effect decrease.

Gamma spectrometry analysis of natural and 2% enriched uranium metal fuel at the RB reactor was performed by germanium gamma spectrometer applying developed computer code ANA. Different samples of the RB reactor uranium fuel, placed at various distances from the Ge detector, were used during measurements. Gamma-ray self-absorption in the fuel material and the geometrical corrections were included in the calculation performed by computer code EFI based on a Monte Carlo method. Evaluated experimental data were used to determine branching ratio for the 1001 keV gamma line of ^234mPa which is in equilibrium with ²³⁸U. Obtained results were in good agreement with the results of other authors. Applied gamma spectrometry method is used for examination of the fresh fuel composition and validation of isotopic enrichment of the 2% enriched uranium fuel at the RB reactor.

We have performed an initial evaluation of a new scatter correction algorithm, Gaussian Subtraction technique, for correction of SPECT images. This technique was evaluated by Monte Carlo simulations.

The Gaussian Subtraction technique uses a non-scatter (standard 20% energy window) and high energy windows. The window on the high energy side of the non-scattered peak is used to fit a Gaussian to the spectral peak. This technique directly determines the number of unscattered photon events detected by a gamma camera.

We find that this scatter correction technique can correct reasonably well (to within 10–15%) for scatter, for the simple phantom cases used here, using scatter windows < ∼ 20 keV wide, for ^99mTc. The Gaussian scatter technique does not require a priori knowledge of source distributions. Implementation of scatter correction would improve image contrast and quantitation in SPECT studies.