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

A Monte Carlo aided method of calculating the average solid angle subtended by a collimated detector from surface and volumetric sources is presented which incorporates the contribution of the collimator edge penetration effect. The validity of the method which utilizes total variance reduction is demonstrated using point reference sources. The results show that the collimator edge penetration effect could be highly significant when measuring photons with energies greater than a few hundred keV and that the method outlined is capable of quantifying the contribution to the calculated average solid angle. Case studies of the possible applications of the method to the field of quantitative photon measurement are presented and discussed.

The main dosimetry characteristics of new liquid systems consisting of Lu, Hf and Zr diphthalocyanine solutions in ethanol, chloroform and their mixtures are investigated. These systems are suitable for measurements of doses of photon and electron radiation and fast neutrons in the absorbed-dose range from 0.002 to 100 kGy at dose rates from 1.5 × 10⁻³ to 3 × 10⁶ Gy/s. The new systems can be used to manufacture compact detectors which acquire absorbed dose information both by measuring their responses with electron spin resonance (ESR) spectrometry or with visible spectrophotometry, and visually by solution color change.

[¹¹C]Methyl triflate ([¹¹C]methyl trifluoromethanesulfonate) was formed in high yield when [¹¹C]methyl iodide in a nitrogen carrier was passed at 200°C through a column containing graphitized carbon impregnated with 50% by weight of silver triflate.

An improved method for the preparation of ^99mTc-radiopharmaceuticals containing the TcN multiple bond, in sterile and apyrogen conditions, is described. This method is based on the reaction of [^99mTc]pertechnetate with ligands derived from S-methyl dithiocarbazate [H₂NN(R)C(S)SCH₃ [R = H, CH₃], in the presence of HCl and tertiary phosphines. It was found that these derivatives can behave both as sources of nitride nitrogen ions (N³⁻) and as coordinating ligands. The reaction leads to the formation of intermediate technetium-nitrido complexes in high yield. These intermediate species can be used as suitable prereduced substrates for the preparation of technetium-nitrido radiopharmaceuticals through simple substitution reactions with appropriate exchanging ligands.

The new radiochemical synthon 1-[¹⁸F]fluoro-2-propanol p-toluenesulfonate 2′a is prepared with a radiochemical yield of 45% [corrected for decay to beginning of synthesis (BOS), synthesis time 40 min]. This compound is used to prepare the [¹⁸F]fluoroisopropyl-alkylated derivatives of benzylamine and norephedrine with a yield of 7 and 2% respectively (BOS, synthesis time 90 min). This alkylation reaction with 2′a gives a good perspective for the preparation of [¹⁸F]fluoro-labelled analogues of β₁-adrenergic receptor binding ligands for PET.

L-683,877, a high affinity, 5-HT₃ selective receptor ligand has been labeled with ¹¹C for use in PET studies to measure regional brain kinetics of L-683,877 and to determine if [¹¹C]L-683,877 can be used for serotonin 5-HT₃ receptor imaging. [¹¹C]L-683,877 was prepared by reacting [¹¹C]methyl iodide with the desmethyl, borane-protected precursor, L-686,472, in DMF in the presence of tetrabutyl ammonium hydroxide. The average specific activity of [¹¹C]L-683,877 was 2700 Ci/mmol and the average radiochemical yield (decay uncorrected) was 20% at the end of synthesis (22 min from EOB).

Increasing use of ¹⁸O-enriched water in biological studies such as those involving doubly labeled water has led to a requirement for a simple cost effective method for analyzing large numbers of ¹⁸O-enriched biological samples. We evaluated the influence of various factors on the precision and accuracy of an equilibration technique in which aqueous samples are equilibrated with CO₂ in evacuated blood collection tubes, Vacutainers^™. Using 10 mL Vacutainers with degassed rubber septa, 1 mL water samples equilibrated in an atmosphere of CO₂ after 16 h on an orbital shaker. δ¹⁸O values became more variable when the sample volume was reduced to 0.25 mL. Varying the evacuation time for the tubes prior to filling with CO₂ between 15 and 75 s had no marked influence on the results. Similarly, sonicating the water samples during this process to remove dissolved gases also had little effect. Bubbling air or CO₂ through the samples prior to analysis led to a reduction in the ¹⁸O content of enriched water samples due to the introduction of ¹⁶O; however, N₂ had no effect on the δ¹⁸O values. Memory effects between samples and instrumental drift were detected with large changes in enrichment (up to 140‰) during mass spectrometric analysis. An analytical procedure and calculations are presented, which in conjunction with two reference waters, may be used to remove these drift effects. This procedure coupled with suggested sample analysis sequences minimizes the influence of memory and allows precision to be optimized. Even in the absence of these precautions, analytical precision on water with δ¹⁸O_V-SMOW content of +30‰ was ca ±0.1‰, and at +175‰ was ±0.37‰, comparable to other ¹⁸O equilibration methods.