Hess E, Blessing G, Coenen H H, Qaim S M
Institut für Nuklearchemie, Forschungszentrum Jülich GmbH, Jülich, Germany.
Appl Radiat Isot. 2000 Jun;52(6):1431-40. doi: 10.1016/s0969-8043(99)00248-1.
An improved aluminium target system for production of elemental fluorine via the 18O(p,n)18F reaction using a two-step irradiation protocol is described. In the first step highly enriched gaseous oxygen-18 is irradiated with protons to form fluorine-18 which gets deposited on the inner target surface. In the second step, after cryogenic recovery of oxygen-18 target gas, a mixture of elemental 'cold' fluorine and krypton is introduced and a short proton irradiation is done, whereby an isotopic exchange between the gaseous fluorine and the deposited radiofluorine occurs. The second step leads to the recovery of the radiofluorine as [18F]fluorine. Optimisation studies were performed regarding the yield and specific radioactivity of [18F]fluorine. Furthermore, some irradiation parameters relevant to the recovery step were investigated. It was found that a 15 to 20 min irradiation with a beam current of 20 microA is sufficient for the isotopic exchange between the fluorine-carrier and the 18F-radioactivity deposited on the inner wall of the target. The distribution of the 18F-radioactivity deposited on the inner target surface is inhomogeneous, probably due to convection effects. Extensive radioanalytical techniques were applied to characterise the reactivity of [18F]fluorine and to identify undesired nonreactive 18F-compounds, mainly [18F]tetrafluoromethane and [18F]nitrogentrifluoride. The [18F]fluorine produced in the system used has the distinction of having a negligible contamination from those inert 18F-compounds. This is a combined effect of the use of highest purity gases and a welded target construction, which avoids any contact of the gases with organic material during irradiations. The target has proved to be very reliable for production of [18F]fluorine in high yields of up to 34 GBq and specific activities of 350-600 GBq/mmol, both at 30 min after end of activation bombardment.
描述了一种改进的铝靶系统，该系统通过两步辐照方案，利用18O(p,n)18F反应生产元素氟。第一步，用质子辐照高浓缩气态氧-18以形成氟-18，氟-18沉积在内部靶表面。第二步，在低温回收氧-18靶气体后，引入元素“冷”氟和氪的混合物并进行短时间质子辐照，从而使气态氟与沉积的放射性氟之间发生同位素交换。第二步导致放射性氟以[18F]氟的形式回收。针对[18F]氟的产率和比活度进行了优化研究。此外，还研究了一些与回收步骤相关的辐照参数。结果发现，以20微安的束流进行15至20分钟的辐照足以使氟载体与沉积在靶内壁上的18F放射性之间发生同位素交换。沉积在内部靶表面的18F放射性分布不均匀，可能是由于对流效应。应用了广泛的放射分析技术来表征[18F]氟的反应性并鉴定不期望的非反应性18F化合物，主要是[18F]四氟甲烷和[18F]三氟化氮。在所用系统中产生的[18F]氟的特点是来自那些惰性18F化合物的污染可忽略不计。这是使用最高纯度气体和焊接靶结构的综合效果，焊接靶结构避免了辐照期间气体与有机材料的任何接触。事实证明，该靶对于生产[18F]氟非常可靠，在活化轰击结束后30分钟时，产率高达34 GBq，比活度为350 - 600 GBq/mmol。
