Improved target system for production of high purity [ 18F]fluorine via the 18O(p,n) 18F reaction

• Published in: Applied radiation and isotopes Vol. 52; no. 6; pp. 1431 - 1440
• Main Authors: Hess, E., Blessing, G., Coenen, H.H., Qaim, S.M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-06-2000
• Subjects: [ 18F]fluorine production; Aluminum; Fluorine Radioisotopes - isolation & purification; Gases - chemistry; Highly enriched 18O-gas target; Inert [ 18F]compounds; Methods; Oxygen Isotopes - chemistry; Specific radioactivity; Specific radioactivity; Inert [ 18F]compounds; [ 18F]fluorine production; Highly enriched 18O-gas target
• ISSN: 0969-8043; 1872-9800
• 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 μA 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.