Bernhard Scholten

Charged-Particle Cross Section Database for Medical Radioisotope Production

Charged-particle cross section database for medical radioisotope production was developed under an international project coordinated by the IAEA. The project focused on radioisotopes for diagnostic purposes and on the related beam monitor reactions. The database contains activation cross-sections of reactions induced by light charged particles with energies mostly up to about 40 MeV. It includes 22 beam monitor reactions for protons (8), deuterons (5), 3He (3) and α-particles (6), and 26 reactions for most commonly used γ-emitters (12), their serious isotopic impurities (4) and β+-emitters (10).

Excitation functions of 124Te(p, xn)124,123I reactions from 6 to 31 MeV with special reference to the production of 124I at a small cyclotron

Abstract Excitation functions were measured by the stacked-foil technique for (p, xn) reactions on highly enriched 124Te in the proton energy range of 6–31 MeV. Thin uniform films of 24Te on Ti-backing were prepared by an electrodeposition method. Above 17 MeV our data agree within experimental errors with the literature values, thus validating the 123I-yields and 124I-impurity levels associated with the 124Te(p, 2n)123I production process. Detailed measurements near the threshold of the 124Te(p, n)124I reaction, on the other hand, show that, contrary to the general assumption, the thick target yield of 124I is fairly high, amounting to 20 MBq (0.54 mCi)/μAh over the optimum energy range Ep = 13 → 9 MeV. A comparison of the three suggested routes for the production of 124I, viz. 124Te(d, 2n)-, 126Te(p, 3n)-, and 124Te(p, n)-processes, is given. The yield and impurity-level data suggest that the 124Te(p, n)124I reaction has a great potential for production at a small cyclotron.

Excitation functions for the cyclotron production of 99mTc and 99Mo

Excitation functions for the Mo-100(p,2n)Tc-99m, Mo-100(p,pn)Mo-99 and Mo-98(p,gamma)Tc-99m nuclear reactions were determined using 97.4 and 99.5% isotopic enrichment of Mo-100 and Mo-98, respectively. The irradiations were performed on three different cyclotrons with overlapping data points from 6 to 65 MeV. The optimum energy range for the Mo-100(p,2n)Tc-99m reaction is 22 --> 12 MeV with a peak at similar to 17 MeV and maximum cross section of similar to 200 mb, Over this energy range the production yield of Tc-99m amounts to 11.2 mCi (415 MBq)/mu A h or 102.8 mCi (3804 MBq)/mu A at saturation. There is no serious radionuclidic impurity problem, Production of Mo-99 is not viable due to the low cross section (similar to 130 mb) over the proton energy range of 30 to 50 MeV. The Mo-98(p,gamma)Tc-99m reaction was found to have a cross section of Tc-99m generator, could consider use of a > 17 MeV proton energy cyclotron for regional production of Tc-99m

Some optimisation studies relevant to the production of high-purity 124I and 120gI at a small-sized cyclotron

Optimisation experiments on the production of the positron emitting radionuclides 124I(T(1/2) = 4.18d) and (120g)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 degrees 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 beta(+) branching in 124I was obtained. Production of 124I was done using 200 mg/cm(2) targets of 99.8% enriched 124TeO(2) on Pt-backing, 16 MeV proton beam intensities of 10 microA, and irradiation times of about 8 h. The average yield of 124I at EOB was 470 MBq(12.7 mCi). At the time of application (about 70 h after EOB) the radionuclidic impurity 123I (T(1/2) = 13.2 h) was <1%. The levels of other impurities were negligible (126I < 0.0001%;125I = 0.01%). Special care was taken to determine the 125I impurity. For the production of (120g)I only a thin 30 mg target (on 0.5 cm(2) area) of 99.9% enriched 120TeO(2) was available. Irradiations were done with 16 MeV protons for 80 min at beam currents of 7 microA. The 120gI yield achieved at EOB was 700 MBq(19 mCi), and the only impurity detected was the isomeric state 120 mI(T(1/2) = 53 min) at a level of 4.0%. The radiochemical purity of both 124I and 120gI 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 microg. High purity 124I and 120gI can thus be advantageously produced on a medium scale using the low-energy (p,n) reaction at a small-sized cyclotron.

Excitation functions of 125Te(p, xn)-reactions from their respective thresholds up to 100 MeV with special reference to the production of 124I.

Excitation functions of the nuclear reactions 125Te(p, xn) (119,120m, 120g, 121,122,123,124,125)I were measured for the first time from their respective thresholds up to 100 MeV using the stacked-foil technique. Thin samples were prepared by electrolytic deposition of 98.3% enriched 125Te on Ti-backing. In addition to experimental studies, excitation functions were calculated by the modified hybrid model code ALICE-IPPE. The experimental and theoretical data generally showed good agreement. From the measured cross section data, integral yields of (123,124,125)I were calculated. The energy range Ep 21 --> 15 MeV appears to be very suitable for the production of the medically interesting radionuclide 124I (T(1/2) = 4.18 d; I(beta)+ = 25%). The thick target yield of 124I amounts to 81 MBq/microA h and the level of 125I-impurity to 0.9%. The 125Te(p,2n)124I reaction gives 124I yield about four times higher than the commonly used 124Te(p,n)124I and 124Te(d,2n)124I reactions. The proposed production energy range is too high for small cyclotrons but large quantities of 124I can be produced with medium-sized commercial machines.

Evaluation of excitation functions of 100Mo(p,d+pn)99Mo and 100Mo (p,2n)99mTc reactions: Estimation of long-lived Tc-impurity and its implication on the specific activity of cyclotron-produced 99mTc

Excitation functions were calculated by the code TALYS for 10 proton-induced reactions on (100)Mo. For (100)Mo(p,d+pn)(99)Mo and (100)Mo(p,2n)(99m)Tc, calculations were also performed using the code STAPRE. Furthermore, for those two reactions and (nat)Mo(p,x)(96)Tc, evaluation of available experimental data was also carried out. The production of (99m)Tc via the (100)Mo(p,2n)-process is discussed. The ratio of atoms of long-lived (99g)Tc and (98)Tc to those of (99m)Tc is appreciably higher in cyclotron production than in generator production of (99m)Tc; this may adversely affect the preparation of (99m)Tc-chelates.

Excitation function of the 18O(p,n)18F nuclear reaction from threshold up to 30 MeV

The available experimental data on the most common route for the production of 18F, viz. 18O(p,n)18F reaction, obtained both via neutron spectral studies and activation measurements, were critically reviewed. In some energy regions the cross section database was found to be rather weak or discrepant. In order to fill the gaps and to clear some of the discrepancies, the excitation function was remeasured from threshold up to 30 MeV using different solid and gas targets containing highly enriched 18O. For this purpose a van de Graaff machine (Ep <4 MeV) and several cyclotrons (Ep = 4-30 MeV) were utilized. The new experimental data help to prepare a recommended data set. At Ep = 14 MeV the integral yield of 18F calculated from the new excitation curve is slightly higher than that from the hitherto accepted data set; at Ep > 14 MeV the yields reported here are new.

Internal irradiation system for excitation function measurement via the stacked-foil technique

Abstract An internal irradiation system has been developed at the injector cyclotron of COSY which allows the use of the conventional stacked-foil technique for excitation function measurement. The beam quality tests consisted of: (i) determination of the beam profile via activity measurement; and (ii) measurement of the proton flux over a wide energy range using monitor reactions of different thresholds. An example of the application of this facility is mentioned.

EXCITATION FUNCTIONS OF DEUTERON INDUCED NUCLEAR REACTIONS ON NATTI UP TO 20 MEV FOR MONITORING DEUTERON BEAMS

Abstract Excitation functions were measured for nuclear reaction on natural Ti leading to the formation of the 43,44m,44g,46,47,48Sc and 48V isotopes up to 21 MeV deuteron energy using the stacked-foil technique. The measured excitation functions, the calculated thick target yield and activity calibration functions for the thin layer activation technique have been compared with the earlier literature data. The investigation with respect to their potential application as monitor reactions showed that the reactions on natTi could be recommended for monitoring deuteron beams, especially the natTi(d,x)48V reaction, in the energy range from 3 up to 20 MeV. However, to clear up the discreancies in the literature and to compare the results with other monitor reactions, additional measurements are required.

Excitation functions of α-particle induced reactions on enriched 123Sb and natSb for production of 124I

Excitation functions of (α,xn) reactions on 98.28% enriched (123)Sb and on (nat)Sb were measured from 9 to 40 MeV. The data could be described well in terms of statistical and precompound models using the code TALYS. The discrepancies in the literature data for the formation of (125)I and (126)I were solved. The nuclear reaction (123)Sb(α,3n)(124)I on an enriched target appears to be interesting for the production of (124)I (T(1/2)=4.18 d) over the energy range E(α)=42→32 MeV, its yield being 11.7 MBq/μAh. The levels of the radionuclidic impurities (125)I and (126)I amount to 1.8% and 0.6%, respectively. The use of (nat)Sb as target material for (124)I production is unsuitable due to the high level of (123)I impurity.