Some optimisation studies relevant to the production of high-purity [formula omitted] and [formula omitted] at a small-sized cyclotron

Abstract

Optimisation experiments on the production of the positron emitting radionuclides 124 I (T 1/2=4.18 d) and 120 g I (T 1/2=1.35 h) were carried out. The TeO 2-target technology and dry distillation method of radioiodine separation were used. The removal of radioiodine was studied as a function of time and the loss of TeO 2 from the target as a function of oven temperature and time of distillation. A distillation time of 15 min at 750°C was found to be ideal. Using a very pure source and comparing the intensities of the annihilation and X-ray radiation, a value of 22.0±0.5% for the β + branching in 124 I was obtained. Production of 124 I was done using 200 mg/ cm 2 targets of 99.8% enriched 124 TeO 2 on Pt-backing, 16 MeV proton beam intensities of 10 μA , and irradiation times of about 8 h . The average yield of 124 I at EOB was 470 MBq (12.7 mCi) . At the time of application (about 70 h after EOB) the radionuclidic impurity 123 I (T 1/2=13.2 h) was <1%. The levels of other impurities were negligible ( 126 I<0.0001%; 125 I=0.01%) . Special care was taken to determine the 125 I impurity. For the production of 120 g I only a thin 30 mg target (on 0.5 cm 2 area) of 99.9% enriched 120 TeO 2 was available. Irradiations were done with 16 MeV protons for 80 min at beam currents of 7 μA . The 120 g I yield achieved at EOB was 700 MBq (19 mCi) , and the only impurity detected was the isomeric state 120 m I (T 1/2=53 min) at a level of 4.0%. The radiochemical purity of both 124 I and 120 g I was checked via HPLC and TLC. The radioiodine collected in 0.02 M NaOH solution existed >98% as iodide. The amount of inactive Te found in radioiodine was <1 μg . High purity 124 I and 120 g I can thus be advantageously produced on a medium scale using the low-energy (p,n) reaction at a small-sized cyclotron.