E. Hess et al., Improved target system for production of high purity [F-18]fluorine via the O-18(p,n)F-18 reaction, APPL RAD IS, 52(6), 2000, pp. 1431-1440
An improved aluminium target system for production of elemental fluorine vi
a the O-18(p,n)F-18 reaction using a two-step irradiation protocol is descr
ibed. In the first step highly enriched gaseous oxygen-18 is irradiated wit
h protons to form fluorine-18 which gets deposited on the inner target surf
ace. In the second step, after cryogenic recovery of oxygen-18 target gas,
a mixture of elemental 'cold' fluorine and krypton is introduced and a shor
t proton irradiation is done, whereby an isotopic exchange between the gase
ous fluorine and the deposited radiofluorine occurs. The second step leads
to the recovery of the radiofluorine as [F-18]fluorine. Optimisation studie
s were performed regarding the yield and specific radioactivity of [F-18]fl
uorine. Furthermore, some irradiation parameters relevant to the recovery s
tep were investigated. It was found that a 15 to 20 min irradiation with a
beam current of 20 CIA is sufficient for the isotopic exchange between the
fluorine-carrier and the F-18-radioactivity deposited on the inner wall of
the target. The distribution of the F-18-radioactivity deposited on the inn
er target surface is inhomogeneous, probably due to convection effects. Ext
ensive radioanalytical techniques were applied to characterise the reactivi
ty of [F-18]fluorine and to identify undesired nonreactive F-18-compounds,
mainly [F-18]tetrafluoromethane and [F-18]nitrogentrifluoride. The [F-18]fl
uorine produced in the system used has the distinction of having a negligib
le contamination from those inert F-18-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 [F-18]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. (C) 2000 Elsevier Sci
ence Ltd. All rights reserved.