Separation of18F Research Articles

Production of Short-Lived Radioisotopes for Nuclear Medicine in Electron Accelerators

Research on the use of photonuclear reactions in the production of isotopes for nuclear medicine is reviewed. The review includes the analysis of distinctive features of isotope production in electron accelerators and assessment of the possibility of such production. The review also presents the results of experimental studies on the production of short-lived 18F, 47Sc, and 67Cu radioisotopes with significantly high total activities in a split microtron with the electron energy of ~55MeV and the separation of 18F and 67Cu with high specific activities from the targets.

Micromachined Pyrolyzed Polymer as a Candidate of 18F- Deposition Electrode toward PET Application

This paper proposes a micromachined pyrolyzed polymer as a candidate for an 18F- deposition electrode for application in positron emission tomography (PET). The electrical separation of 18F from H218O water has been studied for preparing a PET probe. Conventionally, a bulk material such as glassy carbon (GC) is used for the 18F deposition and recovery cell electrode. This study is the first trial using a pyrolyzed polymer as an 18F- deposition and recovery cell electrode. A pyrolyzed polymer electrode is obtained through pyrolysis of batch fabricated polymer patterns while the GC electrode is provided as the bulk material. Pyrolyzed polymer prepared below 1000°C pyrolysis shows similar electrical conductivity as that of GC. Further comparisons between pyrolyzed polymer and GC using Raman spectroscopy and transmission electron microscopy (TEM) were carried out prior to determining the suitability of the material as 18F- deposition and recovery electrode. The deposition and recovery yield of the pyrolyzed polymer electrode derived from the photoresist (AZ4620) at 1000°C was estimated to be 77% and 38%, respectively.

Alpha-activation analysis of nitrogen in boron-doped silicon single crystal

The rapid dissolution of silicon and the substoichiometric separation of18F were studied in order to determine nitrogen in a boron-doped silicon single crystal by α activation analysis via15N(α,n)18F. The silicon dissolution method was developed by using a nitric acid-based solution containing a known amount of ammonium fluoride, instead of hydrofluoric acid, as the18F carrier. The silicon could be dissolved to a depth of 100 μm with a 10 mm O in 9 minutes. The conditions for18F steam distillation and substoichiometric precipitation as lanthanum fluoride were improved. 50% of the fluorine could be separated substoichiometrically even though the carrier amount was increased from 6–12 mmol to more than 16 mmol in order to add it to the dissolving solution. This dissolution method and improved substoichiometric separation were used to determine nitrogen in a boron-doped silicon single crystal. The nitrogen concentration was found to be less than the detection limit (50 ppb).

Determination of fluorine in standard rocks by photon activation analysis

A highly sensitive determination of fluorine in standard rocks by photon activation using the19F(γ,n)18F reaction combined with pyrohydrolysis for the separation of18F has been reported. The irradiation energy was operated at 20 MeV to avoid the interference from Na, because Na is one of the major element in rocks and18F is also produced from Na via23Na(γ,αn)18F reaction above its threshold energy, 20.9 MeV. After irradiation, fluorine was extracted by pyrohydrolysis and separated as LaF3 precipitate. It was ascertained that the average recovery of fluorine in standard rocks was about 90% and the precipitate was of high radiochemical purity. This method was applied to the analysis of ten GSJ rock reference samples and two USGS standard rocks issued by the Geological Survey of Japan and the United States Geological Survey, respectively. The detection limit of this method was 0.02 μg/g, and the results obtained by this method were in good agreement with the recommended values. This method was easily applied to the determination of a few ppm level of fluorine in rock samples, such as ultrabasic rock and feldspar.

Determination of oxygen in fluoride glass by proton activation analysis

Oxygen was determined in three kinds of ZrF4-based fluoride glass [ZrF4−BaF2−GdF3−AlF3 (ZBGA), ZrF4−BaF2−LaF3−YF3−AlF3−LiF−NaF (ZBLYALN) and ZrF4−BaF2−LaF3−YF3−AlF3−LiF (ZBLYAL)] used for fabricating optical fiberby18O(p, n)18F reaction without significant nuclear interference. The main long life96Nb nuclide was produced by the96Zr(p,n) reaction in a non-destructive analysis of ZBGA-fluoride glass and reduced by using a coincidence system with Ge(Li) and NaI(T1) detectors. Substoichiometric separation of18F was also used to determine oxygen in fluoride glass, especially in glass containing yttrium as a component element because the89Zr produced by the89Y(p,n) reaction is a positron emitter, the same as18F. It was confirmed that the oxygen concentration in fluoride glass was 13–2460 ppm related to the loss by scattering.

Production of18F using a natural water target at the CV-28 cyclotron at IPEN-CNEN/SP

The development of an automated water target for the production of18F is described. The system was fully fested and shown to be reliable and secure. The chemical separation of18F was carried out using an anionexchange resin and K2CO3 as eluent. The18F production yields were, on average, (4.81±0.42) MBq/μAh and the specific activity was higher than 6.623×105 MBq/mmol. Heat transfer measurements and calculations were made.

Determination of oxygen impurity in high purity materials by charged particle activation analysis using alpha projectiles

40 MeV α-particles have been used to determine oxygen impurity at ppm levels in silicon, copper, and stainless steel, through the radiochemical separation of18F from the matrix. The separation of18F has been carried out by two techniques, viz.(1) distillation of H2SiF6 and (2) precipitation of KBF4 and some modification has been applied in the separation, depending on the nature of interferences from the matrix. Instrumental approach was also carried out to determine the oxygen impurity at ≥ 100 ppm in Si matrix because this approach is not possible in Cu and stainless steel samples due to matrix activity.

Determination of oxygen in alkali halide salts by proton activation and radiochemical separation

A lanthanum fluoride precipitation method for the separation of18F produced from the18O(p,n)18F reaction in alkali halide salts is described. This radiochemical separation method minimizes interferences from other positron emitters produced by proton bombardment and makes the accurate determination of ppm-level18O in complex alkali halide systems feasible. The interference from the19F(p,d)18F reaction is eliminated by keeping the proton energy less than 8.2 MeV. Applications of this technique to studies of dissolved oxide species in molten alkali halide salts are discussed.

Charged-particle activation analysis studies on carbon, nitrogen and oxygen mainly in semiconductor silicon

High utility value of charged-particle activation analysis is exemplified by the study on carbon, nitrogen and oxygen in semiconductor silicon. A summary of the present authors' works is shown, and the equilibrium of carbon and oxygen in a silicon melt with ambient carbon monoxide is discussed. Also, a note is given about the chemical separation of18F for the3He activation analysis of various matrices.